fsp0fsp.cc

/*****************************************************************************

Copyright (c) 1995, 2016, Oracle and/or its affiliates. All Rights Reserved.
Copyright (c) 2017, 2023, MariaDB Corporation.

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; version 2 of the License.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA

*****************************************************************************/

/******************************************************************//**
@file fsp/fsp0fsp.cc
File space management

Created 11/29/1995 Heikki Tuuri
***********************************************************************/

#include <memory>
#include <cctype>
#include <cstdlib>
#include <thread>

#include "fsp0fsp.h"
#include "buf0buf.h"
#include "buf0flu.h"
#include "fil0fil.h"
#include "fil0crypt.h"
#include "mtr0log.h"
#include "ut0byte.h"
#include "page0page.h"
#include "srv0srv.h"
#include "srv0start.h"
#include "btr0btr.h"
#include "btr0sea.h"
#include "dict0boot.h"
#include "log0log.h"
#include "dict0mem.h"
#include "fsp0types.h"
#include "log.h"
#include "trx0trx.h"

/** Returns the first extent descriptor for a segment.
We think of the extent lists of the segment catenated in the order
FSEG_FULL -> FSEG_NOT_FULL -> FSEG_FREE.
@param[in]	inode		segment inode
@param[in]	space		tablespace
@param[in,out]	mtr		mini-transaction
@param[out]	err		error code
@return the first extent descriptor, or NULL if none */
MY_ATTRIBUTE((nonnull, warn_unused_result))
static
xdes_t*
fseg_get_first_extent(
	fseg_inode_t*		inode,
	const fil_space_t*	space,
	mtr_t*			mtr,
	dberr_t*		err);

ATTRIBUTE_COLD MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Put new extents to the free list if there are free extents above the free
limit. If an extent happens to contain an extent descriptor page, the extent
is put to the FSP_FREE_FRAG list with the page marked as used.
@param[in]	init_space	true if this is a single-table tablespace
and we are only initializing the first extent and the first bitmap pages;
then we will not allocate more extents
@param[in,out]	space		tablespace
@param[in,out]	header		tablespace header
@param[in,out]	mtr		mini-transaction */
static
dberr_t
fsp_fill_free_list(
	bool		init_space,
	fil_space_t*	space,
	buf_block_t*	header,
	mtr_t*		mtr);

/** Allocates a single free page from a segment.
This function implements the intelligent allocation strategy which tries to
minimize file space fragmentation.
@param[in,out]	space			tablespace
@param[in,out]	seg_inode		segment inode
@param[in,out]	iblock			segment inode page
@param[in]	hint			hint of which page would be desirable
@param[in]	direction		if the new page is needed because of
an index page split, and records are inserted there in order, into which
direction they go alphabetically: FSP_DOWN, FSP_UP, FSP_NO_DIR
@param[in,out]	mtr			mini-transaction
@param[in,out]	init_mtr		mtr or another mini-transaction in
which the page should be initialized.
@param[out]	err			error code
@return the allocated page
@retval nullptr	if no page could be allocated */
static
buf_block_t*
fseg_alloc_free_page_low(
	fil_space_t*		space,
	fseg_inode_t*		seg_inode,
	buf_block_t*		iblock,
	uint32_t		hint,
	byte			direction,
#ifdef UNIV_DEBUG
	bool			has_done_reservation,
	/*!< whether the space has already been reserved */
#endif /* UNIV_DEBUG */
	mtr_t*			mtr,
	mtr_t*			init_mtr,
	dberr_t*		err)
	MY_ATTRIBUTE((nonnull, warn_unused_result));

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Get the tablespace header block, SX-latched
@param[in]      space           tablespace
@param[in,out]  mtr             mini-transaction
@param[out]     err             error code
@return pointer to the space header, page x-locked
@retval nullptr if the page cannot be retrieved or is corrupted */
static buf_block_t *fsp_get_header(const fil_space_t *space, mtr_t *mtr,
                                   dberr_t *err)
{
  const page_id_t id{space->id, 0};
  buf_block_t *block= mtr->get_already_latched(id, MTR_MEMO_PAGE_SX_FIX);
  if (block)
    *err= DB_SUCCESS;
  else
  {
    block= buf_page_get_gen(id, space->zip_size(), RW_SX_LATCH,
                            nullptr, BUF_GET_POSSIBLY_FREED,
                            mtr, err);
    if (block &&
        space->id != mach_read_from_4(FSP_HEADER_OFFSET + FSP_SPACE_ID +
                                      block->page.frame))
    {
      *err= DB_CORRUPTION;
      block= nullptr;
    }
  }
  return block;
}

/** Set the XDES_FREE_BIT of a page.
@tparam         free    desired value of XDES_FREE_BIT
@param[in]      block   extent descriptor block
@param[in,out]  descr   extent descriptor
@param[in]      offset  page offset within the extent
@param[in,out]  mtr     mini-transaction */
template<bool free>
inline void xdes_set_free(const buf_block_t &block, xdes_t *descr,
                          ulint offset, mtr_t *mtr)
{
  ut_ad(mtr->memo_contains_flagged(&block, MTR_MEMO_PAGE_SX_FIX |
                                   MTR_MEMO_PAGE_X_FIX));
  ut_ad(offset < FSP_EXTENT_SIZE);
  ut_ad(page_align(descr) == block.page.frame);
  compile_time_assert(XDES_BITS_PER_PAGE == 2);
  compile_time_assert(XDES_FREE_BIT == 0);
  compile_time_assert(XDES_CLEAN_BIT == 1);

  ulint index= XDES_BITS_PER_PAGE * offset;
  byte *b= &descr[XDES_BITMAP + (index >> 3)];
  /* xdes_init() should have set all XDES_CLEAN_BIT. */
  ut_ad(!(~*b & 0xaa));
  /* Clear or set XDES_FREE_BIT. */
  byte val= free
    ? static_cast<byte>(*b | 1 << (index & 7))
    : static_cast<byte>(*b & ~(1 << (index & 7)));
  mtr->write<1>(block, b, val);
}

/**
Find a free page.
@param descr   extent descriptor
@param hint    page offset to start searching from (towards larger pages)
@return free page offset
@retval FIL_NULL if no page is free */
inline uint32_t xdes_find_free(const xdes_t *descr, uint32_t hint= 0)
{
  const uint32_t extent_size= FSP_EXTENT_SIZE;
  ut_ad(hint < extent_size);
  for (uint32_t i= hint; i < extent_size; i++)
    if (xdes_is_free(descr, i))
      return i;
  for (uint32_t i= 0; i < hint; i++)
    if (xdes_is_free(descr, i))
      return i;
  return FIL_NULL;
}

/**
Determine the number of used pages in a descriptor.
@param descr  file descriptor
@return number of pages used */
inline uint32_t xdes_get_n_used(const xdes_t *descr)
{
  uint32_t count= 0;

  for (uint32_t i= FSP_EXTENT_SIZE; i--; )
    if (!xdes_is_free(descr, i))
      count++;

  return count;
}

/**
Determine whether a file extent is full.
@param descr  file descriptor
@return whether all pages have been allocated */
inline bool xdes_is_full(const xdes_t *descr)
{
  return FSP_EXTENT_SIZE == xdes_get_n_used(descr);
}

/** Set the state of an extent descriptor.
@param[in]      block   extent descriptor block
@param[in,out]  descr   extent descriptor
@param[in]      state   the state
@param[in,out]  mtr     mini-transaction */
inline void xdes_set_state(const buf_block_t &block, xdes_t *descr,
                           byte state, mtr_t *mtr)
{
  ut_ad(descr && mtr);
  ut_ad(state >= XDES_FREE);
  ut_ad(state <= XDES_FSEG);
  ut_ad(mtr->memo_contains_flagged(&block, MTR_MEMO_PAGE_SX_FIX |
                                   MTR_MEMO_PAGE_X_FIX));
  ut_ad(page_align(descr) == block.page.frame);
  ut_ad(mach_read_from_4(descr + XDES_STATE) <= XDES_FSEG);
  mtr->write<1>(block, XDES_STATE + 3 + descr, state);
}

/**********************************************************************//**
Gets the state of an xdes.
@return state */
UNIV_INLINE
ulint
xdes_get_state(
/*===========*/
	const xdes_t*	descr)	/*!< in: descriptor */
{
	ulint	state;

	ut_ad(descr);
	state = mach_read_from_4(descr + XDES_STATE);
	ut_ad(state - 1 < XDES_FSEG);
	return(state);
}

/**********************************************************************//**
Inits an extent descriptor to the free and clean state. */
inline void xdes_init(const buf_block_t &block, xdes_t *descr, mtr_t *mtr)
{
  ut_ad(mtr->memo_contains_flagged(&block, MTR_MEMO_PAGE_SX_FIX |
                                   MTR_MEMO_PAGE_X_FIX));
  mtr->memset(&block, uint16_t(descr - block.page.frame) + XDES_BITMAP,
              XDES_SIZE - XDES_BITMAP, 0xff);
  xdes_set_state(block, descr, XDES_FREE, mtr);
}

/** Mark a page used in an extent descriptor.
@param[in,out]  seg_inode       segment inode
@param[in,out]  iblock          segment inode page
@param[in]      page            page number
@param[in,out]  descr           extent descriptor
@param[in,out]  xdes            extent descriptor page
@param[in,out]  mtr             mini-transaction
@return error code */
static MY_ATTRIBUTE((nonnull, warn_unused_result))
dberr_t
fseg_mark_page_used(fseg_inode_t *seg_inode, buf_block_t *iblock,
                    ulint page, xdes_t *descr, buf_block_t *xdes, mtr_t *mtr)
{
  ut_ad(fil_page_get_type(iblock->page.frame) == FIL_PAGE_INODE);
  ut_ad(!((page_offset(seg_inode) - FSEG_ARR_OFFSET) % FSEG_INODE_SIZE));
  ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + seg_inode, 4));
  ut_ad(!memcmp(seg_inode + FSEG_ID, descr + XDES_ID, 4));

  const uint16_t xoffset= uint16_t(descr - xdes->page.frame + XDES_FLST_NODE);
  const uint16_t ioffset= uint16_t(seg_inode - iblock->page.frame);

  if (!xdes_get_n_used(descr))
  {
    /* We move the extent from the free list to the NOT_FULL list */
    if (dberr_t err= flst_remove(iblock, uint16_t(FSEG_FREE + ioffset),
                                 xdes, xoffset, mtr))
      return err;
    if (dberr_t err= flst_add_last(iblock, uint16_t(FSEG_NOT_FULL + ioffset),
                                   xdes, xoffset, mtr))
      return err;
  }

  if (UNIV_UNLIKELY(!xdes_is_free(descr, page % FSP_EXTENT_SIZE)))
    return DB_CORRUPTION;

  /* We mark the page as used */
  xdes_set_free<false>(*xdes, descr, page % FSP_EXTENT_SIZE, mtr);

  byte* p_not_full= seg_inode + FSEG_NOT_FULL_N_USED;
  const uint32_t not_full_n_used= mach_read_from_4(p_not_full) + 1;
  mtr->write<4>(*iblock, p_not_full, not_full_n_used);
  if (xdes_is_full(descr))
  {
    /* We move the extent from the NOT_FULL list to the FULL list */
    if (dberr_t err= flst_remove(iblock, uint16_t(FSEG_NOT_FULL + ioffset),
                                 xdes, xoffset, mtr))
      return err;
    if (dberr_t err= flst_add_last(iblock, uint16_t(FSEG_FULL + ioffset),
                                   xdes, xoffset, mtr))
      return err;
    mtr->write<4>(*iblock, seg_inode + FSEG_NOT_FULL_N_USED,
                  not_full_n_used - FSP_EXTENT_SIZE);
  }

  return DB_SUCCESS;
}

/** Get pointer to a the extent descriptor of a page.
@param[in,out]	sp_header	tablespace header page, x-latched
@param[in]	space		tablespace
@param[in]	offset		page offset
@param[in,out]	mtr		mini-transaction
@param[out]	err		error code
@param[out]	desc_block	descriptor block
@param[in]	init_space	whether the tablespace is being initialized
@return pointer to the extent descriptor, NULL if the page does not
exist in the space or if the offset exceeds free limit */
UNIV_INLINE MY_ATTRIBUTE((warn_unused_result))
xdes_t*
xdes_get_descriptor_with_space_hdr(
	buf_block_t*		header,
	const fil_space_t*	space,
	uint32_t		offset,
	mtr_t*			mtr,
	dberr_t*		err = nullptr,
	buf_block_t**		desc_block = nullptr,
	bool			init_space = false)
{
	ut_ad(space->is_owner());
	ut_ad(mtr->memo_contains_flagged(header, MTR_MEMO_PAGE_SX_FIX
					 | MTR_MEMO_PAGE_X_FIX));
	/* Read free limit and space size */
	uint32_t limit = mach_read_from_4(FSP_HEADER_OFFSET + FSP_FREE_LIMIT
					  + header->page.frame);
	uint32_t size  = mach_read_from_4(FSP_HEADER_OFFSET + FSP_SIZE
					  + header->page.frame);
	ut_ad(limit == space->free_limit
	      || (space->free_limit == 0
		  && (init_space
		      || space->purpose == FIL_TYPE_TEMPORARY
		      || (srv_startup_is_before_trx_rollback_phase
			  && (space->id == TRX_SYS_SPACE
			      || srv_is_undo_tablespace(space->id))))));
	ut_ad(size == space->size_in_header);

	if (offset >= size || offset >= limit) {
		return nullptr;
	}

	const unsigned zip_size = space->zip_size();

	uint32_t descr_page_no = xdes_calc_descriptor_page(zip_size, offset);

	buf_block_t* block = header;

	if (descr_page_no) {
		block = buf_page_get_gen(page_id_t(space->id, descr_page_no),
					 zip_size, RW_SX_LATCH, nullptr,
					 BUF_GET_POSSIBLY_FREED, mtr, err);
	}

	if (desc_block) {
		*desc_block = block;
	}

	return block
		? XDES_ARR_OFFSET + XDES_SIZE
		* xdes_calc_descriptor_index(zip_size, offset)
		+ block->page.frame
		: nullptr;
}

MY_ATTRIBUTE((nonnull(1,3), warn_unused_result))
/** Get the extent descriptor of a page.
The page where the extent descriptor resides is x-locked. If the page
offset is equal to the free limit of the space, we will add new
extents from above the free limit to the space free list, if not free
limit == space size. This adding is necessary to make the descriptor
defined, as they are uninitialized above the free limit.
@param[in]	space		tablespace
@param[in]	offset		page offset; if equal to the free limit, we
try to add new extents to the space free list
@param[in,out]	mtr		mini-transaction
@param[out]	err		error code
@param[out]	xdes		extent descriptor page
@return the extent descriptor */
static xdes_t *xdes_get_descriptor(const fil_space_t *space, uint32_t offset,
                                   mtr_t *mtr, dberr_t *err= nullptr,
                                   buf_block_t **xdes= nullptr)
{
  if (buf_block_t *block=
      buf_page_get_gen(page_id_t(space->id, 0), space->zip_size(), RW_SX_LATCH,
                       nullptr, BUF_GET_POSSIBLY_FREED, mtr, err))
    return xdes_get_descriptor_with_space_hdr(block, space, offset, mtr,
                                              err, xdes);
  return nullptr;
}

MY_ATTRIBUTE((nonnull(3), warn_unused_result))
/** Get a pointer to the extent descriptor. The page where the
extent descriptor resides is x-locked.
@param space    tablespace
@param lst_node file address of the list node contained in the descriptor
@param mtr      mini-transaction
@param err      error code
@param block    extent descriptor block
@return pointer to the extent descriptor */
static inline
xdes_t *xdes_lst_get_descriptor(const fil_space_t &space, fil_addr_t lst_node,
                                mtr_t *mtr, buf_block_t **block= nullptr,
                                dberr_t *err= nullptr)
{
  ut_ad(mtr->memo_contains(space));
  ut_ad(lst_node.boffset < space.physical_size());
  buf_block_t *b;
  if (!block)
    block= &b;
  *block= buf_page_get_gen(page_id_t{space.id, lst_node.page},
                           space.zip_size(), RW_SX_LATCH,
                           nullptr, BUF_GET_POSSIBLY_FREED, mtr, err);
  if (*block)
    return (*block)->page.frame + lst_node.boffset - XDES_FLST_NODE;

  space.set_corrupted();
  return nullptr;
}

/********************************************************************//**
Returns page offset of the first page in extent described by a descriptor.
@return offset of the first page in extent */
static uint32_t xdes_get_offset(const xdes_t *descr)
{
  ut_ad(descr);
  return page_get_page_no(page_align(descr)) +
    uint32_t(((page_offset(descr) - XDES_ARR_OFFSET) / XDES_SIZE) *
             FSP_EXTENT_SIZE);
}

/** Initialize a file page whose prior contents should be ignored.
@param[in,out]	block	buffer pool block */
void fsp_apply_init_file_page(buf_block_t *block)
{
  memset_aligned<UNIV_PAGE_SIZE_MIN>(block->page.frame, 0, srv_page_size);
  const page_id_t id(block->page.id());

  mach_write_to_4(block->page.frame + FIL_PAGE_OFFSET, id.page_no());
  memset_aligned<8>(block->page.frame + FIL_PAGE_PREV, 0xff, 8);
  mach_write_to_4(block->page.frame + FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID,
                  id.space());
  if (page_zip_des_t* page_zip= buf_block_get_page_zip(block))
  {
    memset_aligned<UNIV_ZIP_SIZE_MIN>(page_zip->data, 0,
                                      page_zip_get_size(page_zip));
    static_assert(FIL_PAGE_OFFSET == 4, "compatibility");
    memcpy_aligned<4>(page_zip->data + FIL_PAGE_OFFSET,
                      block->page.frame + FIL_PAGE_OFFSET, 4);
    memset_aligned<8>(page_zip->data + FIL_PAGE_PREV, 0xff, 8);
    static_assert(FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID % 4 == 2,
                  "not perfect alignment");
    memcpy_aligned<2>(page_zip->data + FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID,
                      block->page.frame + FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID, 4);
  }
}

#ifdef UNIV_DEBUG
/** Assert that the mini-transaction is compatible with
updating an allocation bitmap page.
@param[in]	mtr	mini-transaction */
void fil_space_t::modify_check(const mtr_t& mtr) const
{
  switch (mtr.get_log_mode()) {
  case MTR_LOG_NONE:
    /* These modes are only allowed within a non-bitmap page
       when there is a higher-level redo log record written. */
    ut_ad(purpose == FIL_TYPE_TABLESPACE || purpose == FIL_TYPE_TEMPORARY);
    break;
  case MTR_LOG_NO_REDO:
    ut_ad(purpose == FIL_TYPE_TEMPORARY || purpose == FIL_TYPE_IMPORT);
    break;
  default:
    /* We may only write redo log for a persistent tablespace. */
    ut_ad(purpose == FIL_TYPE_TABLESPACE);
    ut_ad(mtr.is_named_space(id) ||
          id == SRV_SPACE_ID_BINLOG0 || id == SRV_SPACE_ID_BINLOG1);
  }
}
#endif

/** Initialize a tablespace header.
@param[in,out]	space	tablespace
@param[in]	size	current size in blocks
@param[in,out]	mtr	mini-transaction
@return error code */
dberr_t fsp_header_init(fil_space_t *space, uint32_t size, mtr_t *mtr)
{
	const page_id_t page_id(space->id, 0);
	const ulint zip_size = space->zip_size();

	buf_block_t *free_block = buf_LRU_get_free_block(have_no_mutex);

	mtr->x_lock_space(space);

	buf_block_t* block = buf_page_create(space, 0, zip_size, mtr,
					     free_block);
	if (UNIV_UNLIKELY(block != free_block)) {
		buf_pool.free_block(free_block);
	}

	space->size_in_header = size;
	space->free_len = 0;
	space->free_limit = 0;

	/* The prior contents of the file page should be ignored */

	fsp_init_file_page(space, block, mtr);

	mtr->write<2>(*block, block->page.frame + FIL_PAGE_TYPE,
		      FIL_PAGE_TYPE_FSP_HDR);

	mtr->write<4,mtr_t::MAYBE_NOP>(*block, FSP_HEADER_OFFSET + FSP_SPACE_ID
				       + block->page.frame, space->id);
	ut_ad(0 == mach_read_from_4(FSP_HEADER_OFFSET + FSP_NOT_USED
				    + block->page.frame));
	/* recv_sys_t::parse() expects to find a WRITE record that
	covers all 4 bytes. Therefore, we must specify mtr_t::FORCED
	in order to avoid optimizing away any unchanged most
	significant bytes of FSP_SIZE. */
	mtr->write<4,mtr_t::FORCED>(*block, FSP_HEADER_OFFSET + FSP_SIZE
				    + block->page.frame, size);
	ut_ad(0 == mach_read_from_4(FSP_HEADER_OFFSET + FSP_FREE_LIMIT
				    + block->page.frame));
	if (auto f = space->flags & ~FSP_FLAGS_MEM_MASK) {
		mtr->write<4,mtr_t::FORCED>(*block,
					    FSP_HEADER_OFFSET + FSP_SPACE_FLAGS
					    + block->page.frame, f);
	}
	ut_ad(0 == mach_read_from_4(FSP_HEADER_OFFSET + FSP_FRAG_N_USED
				    + block->page.frame));

	flst_init(block, FSP_HEADER_OFFSET + FSP_FREE, mtr);
	flst_init(block, FSP_HEADER_OFFSET + FSP_FREE_FRAG, mtr);
	flst_init(block, FSP_HEADER_OFFSET + FSP_FULL_FRAG, mtr);
	flst_init(block, FSP_HEADER_OFFSET + FSP_SEG_INODES_FULL, mtr);
	flst_init(block, FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE, mtr);

	mtr->write<8>(*block, FSP_HEADER_OFFSET + FSP_SEG_ID
		      + block->page.frame,
		      1U);

	if (dberr_t err = fsp_fill_free_list(!is_system_tablespace(space->id),
					     space, block, mtr)) {
		return err;
	}

	/* Write encryption metadata to page 0 if tablespace is
	encrypted or encryption is disabled by table option. */
	if (space->crypt_data &&
	    (space->crypt_data->should_encrypt() ||
	     space->crypt_data->not_encrypted())) {
		space->crypt_data->write_page0(block, mtr);
	}

	return DB_SUCCESS;
}

/** Try to extend a single-table tablespace so that a page would fit in the
data file.
@param[in,out]	space	tablespace
@param[in]	page_no	page number
@param[in,out]	header	tablespace header
@param[in,out]	mtr	mini-transaction
@return true if success */
static ATTRIBUTE_COLD __attribute__((warn_unused_result))
bool
fsp_try_extend_data_file_with_pages(
	fil_space_t*	space,
	uint32_t	page_no,
	buf_block_t*	header,
	mtr_t*		mtr)
{
	bool	success;
	ulint	size;

	ut_ad(!is_system_tablespace(space->id));
	ut_d(space->modify_check(*mtr));

	size = mach_read_from_4(FSP_HEADER_OFFSET + FSP_SIZE
				+ header->page.frame);
	ut_ad(size == space->size_in_header);

	ut_a(page_no >= size);

	success = fil_space_extend(space, page_no + 1);
	/* The size may be less than we wanted if we ran out of disk space. */
	/* recv_sys_t::parse() expects to find a WRITE record that
	covers all 4 bytes. Therefore, we must specify mtr_t::FORCED
	in order to avoid optimizing away any unchanged most
	significant bytes of FSP_SIZE. */
	mtr->write<4,mtr_t::FORCED>(*header, FSP_HEADER_OFFSET + FSP_SIZE
				    + header->page.frame, space->size);
	space->size_in_header = space->size;

	return(success);
}

/** Calculate the number of physical pages in an extent for this file.
@param[in]	physical_size	page_size of the datafile
@return number of pages in an extent for this file */
inline uint32_t fsp_get_extent_size_in_pages(ulint physical_size)
{
  return uint32_t((FSP_EXTENT_SIZE << srv_page_size_shift) / physical_size);
}


/** Calculate the number of pages to extend a datafile.
We extend single-table tablespaces first one extent at a time,
but 4 at a time for bigger tablespaces. It is not enough to extend always
by one extent, because we need to add at least one extent to FSP_FREE.
A single extent descriptor page will track many extents. And the extent
that uses its extent descriptor page is put onto the FSP_FREE_FRAG list.
Extents that do not use their extent descriptor page are added to FSP_FREE.
The physical page size is used to determine how many extents are tracked
on one extent descriptor page. See xdes_calc_descriptor_page().
@param[in]	physical_size	page size in data file
@param[in]	size		current number of pages in the datafile
@return number of pages to extend the file. */
static uint32_t fsp_get_pages_to_extend_ibd(unsigned physical_size,
					    uint32_t size)
{
	uint32_t extent_size = fsp_get_extent_size_in_pages(physical_size);
	/* The threshold is set at 32MiB except when the physical page
	size is small enough that it must be done sooner. */
	uint32_t threshold = std::min(32 * extent_size, physical_size);

	if (size >= threshold) {
		/* Below in fsp_fill_free_list() we assume
		that we add at most FSP_FREE_ADD extents at
		a time */
		extent_size *= FSP_FREE_ADD;
	}

	return extent_size;
}

/** Try to extend the last data file of a tablespace if it is auto-extending.
@param[in,out]	space	tablespace
@param[in,out]	header	tablespace header
@param[in,out]	mtr	mini-transaction
@return	number of pages added
@retval	0 if the tablespace was not extended */
ATTRIBUTE_COLD __attribute__((nonnull))
static
ulint
fsp_try_extend_data_file(fil_space_t *space, buf_block_t *header, mtr_t *mtr)
{
	const char* OUT_OF_SPACE_MSG =
		"ran out of space. Please add another file or use"
		" 'autoextend' for the last file in setting";

	ut_d(space->modify_check(*mtr));

	if (space->id == TRX_SYS_SPACE
	    && !srv_sys_space.can_auto_extend_last_file()) {

		/* We print the error message only once to avoid
		spamming the error log. Note that we don't need
		to reset the flag to false as dealing with this
		error requires server restart. */
		if (!srv_sys_space.get_tablespace_full_status()) {
			sql_print_error("InnoDB: The InnoDB system tablespace "
                                        "%s" " innodb_data_file_path.",
                                        OUT_OF_SPACE_MSG);
			srv_sys_space.set_tablespace_full_status(true);
		}
		return(0);
	} else if (space->id == SRV_TMP_SPACE_ID
		   && !srv_tmp_space.can_auto_extend_last_file()) {

		/* We print the error message only once to avoid
		spamming the error log. Note that we don't need
		to reset the flag to false as dealing with this
		error requires server restart. */
		if (!srv_tmp_space.get_tablespace_full_status()) {
			sql_print_error("InnoDB: The InnoDB temporary"
                                        " tablespace %s"
                                        " innodb_temp_data_file_path.",
                                        OUT_OF_SPACE_MSG);
			srv_tmp_space.set_tablespace_full_status(true);
		}
		return(0);
	}

	uint32_t size = mach_read_from_4(FSP_HEADER_OFFSET + FSP_SIZE
					 + header->page.frame);
	ut_ad(size == space->size_in_header);
	uint32_t size_increase;

	const unsigned ps = space->physical_size();

	switch (space->id) {
	case TRX_SYS_SPACE:
		size_increase = srv_sys_space.get_increment();
		break;
	case SRV_TMP_SPACE_ID:
		size_increase = srv_tmp_space.get_increment();
		break;
	default:
		uint32_t extent_pages = fsp_get_extent_size_in_pages(ps);
		if (size < extent_pages) {
			/* Let us first extend the file to extent_size */
			if (!fsp_try_extend_data_file_with_pages(
				    space, extent_pages - 1, header, mtr)) {
				return(0);
			}

			size = extent_pages;
		}

		size_increase = fsp_get_pages_to_extend_ibd(ps, size);
	}

	if (size_increase == 0) {
		return(0);
	}

	if (!fil_space_extend(space, size + size_increase)) {
		return(0);
	}

	/* For the system tablespace, we ignore any fragments of a
	full megabyte when storing the size to the space header */

	space->size_in_header = space->id
		? space->size
		: ut_2pow_round(space->size, (1024 * 1024) / ps);

	/* recv_sys_t::parse() expects to find a WRITE record that
	covers all 4 bytes. Therefore, we must specify mtr_t::FORCED
	in order to avoid optimizing away any unchanged most
	significant bytes of FSP_SIZE. */
	mtr->write<4,mtr_t::FORCED>(*header, FSP_HEADER_OFFSET + FSP_SIZE
				    + header->page.frame,
				    space->size_in_header);

	return(size_increase);
}

/** Reset the page type.
Data files created before MySQL 5.1.48 may contain garbage in FIL_PAGE_TYPE.
In MySQL 3.23.53, only undo log pages and index pages were tagged.
Any other pages were written with uninitialized bytes in FIL_PAGE_TYPE.
@param[in]	block	block with invalid FIL_PAGE_TYPE
@param[in]	type	expected page type
@param[in,out]	mtr	mini-transaction */
ATTRIBUTE_COLD
void fil_block_reset_type(const buf_block_t& block, ulint type, mtr_t* mtr)
{
  ib::info() << "Resetting invalid page " << block.page.id() << " type "
             << fil_page_get_type(block.page.frame) << " to " << type << ".";
  mtr->write<2>(block, block.page.frame + FIL_PAGE_TYPE, type);
}

/** Put new extents to the free list if there are free extents above the free
limit. If an extent happens to contain an extent descriptor page, the extent
is put to the FSP_FREE_FRAG list with the page marked as used.
@param[in]	init_space	true if this is a single-table tablespace
and we are only initializing the first extent and the first bitmap pages;
then we will not allocate more extents
@param[in,out]	space		tablespace
@param[in,out]	header		tablespace header
@param[in,out]	mtr		mini-transaction
@return error code */
static
dberr_t
fsp_fill_free_list(
	bool		init_space,
	fil_space_t*	space,
	buf_block_t*	header,
	mtr_t*		mtr)
{
  ut_d(space->modify_check(*mtr));

  /* Check if we can fill free list from above the free list limit */
  uint32_t size=
    mach_read_from_4(FSP_HEADER_OFFSET + FSP_SIZE + header->page.frame);
  uint32_t limit=
    mach_read_from_4(FSP_HEADER_OFFSET + FSP_FREE_LIMIT + header->page.frame);

  ut_ad(size == space->size_in_header);
  ut_ad(limit == space->free_limit);

  const auto zip_size= space->zip_size();

  if (size < limit + FSP_EXTENT_SIZE * FSP_FREE_ADD)
  {
    bool skip_resize= init_space;
    switch (space->id) {
    case TRX_SYS_SPACE:
      skip_resize= !srv_sys_space.can_auto_extend_last_file();
      break;
    case SRV_TMP_SPACE_ID:
      skip_resize= !srv_tmp_space.can_auto_extend_last_file();
      break;
    }

    if (!skip_resize)
    {
      fsp_try_extend_data_file(space, header, mtr);
      size= space->size_in_header;
    }
  }

  uint32_t count= 0;
  for (uint32_t i= limit, extent_size= FSP_EXTENT_SIZE,
         physical_size= space->physical_size();
       (init_space && i < 1) ||
         (i + extent_size <= size && count < FSP_FREE_ADD);
       i += extent_size)
  {
    const bool init_xdes= !ut_2pow_remainder(i, physical_size);
    space->free_limit= i + extent_size;
    mtr->write<4>(*header, FSP_HEADER_OFFSET + FSP_FREE_LIMIT +
                  header->page.frame, i + extent_size);

    if (init_xdes)
    {
      /* We are going to initialize a new descriptor page
      and a new ibuf bitmap page: the prior contents of the
      pages should be ignored. */

      if (i)
      {
        buf_block_t *f= buf_LRU_get_free_block(have_no_mutex);
        buf_block_t *block= buf_page_create(space, i, zip_size, mtr, f);
        if (UNIV_UNLIKELY(block != f))
          buf_pool.free_block(f);
        fsp_init_file_page(space, block, mtr);
        mtr->write<2>(*block, FIL_PAGE_TYPE + block->page.frame,
                      FIL_PAGE_TYPE_XDES);
      }

      if (space->purpose != FIL_TYPE_TEMPORARY)
      {
        buf_block_t *f= buf_LRU_get_free_block(have_no_mutex);
        buf_block_t *block=
          buf_page_create(space, i + 1, zip_size, mtr, f);
        if (UNIV_UNLIKELY(block != f))
          buf_pool.free_block(f);
        /* The zero-initialization will reset the change buffer bitmap bits
        to safe values for possible import to an earlier version that
        supports change buffering:

        IBUF_BITMAP_FREE     = 0 (no space left for buffering inserts)
        IBUF_BITMAP_BUFFERED = 0 (no changes have been buffered)
        IBUF_BITMAP_IBUF     = 0 (not part of the change buffer) */
        fsp_init_file_page(space, block, mtr);
        mtr->write<2>(*block, FIL_PAGE_TYPE + block->page.frame,
                      FIL_PAGE_IBUF_BITMAP);
      }
    }

    buf_block_t *xdes= nullptr;
    xdes_t *descr;
    {
      dberr_t err= DB_SUCCESS;
      descr= xdes_get_descriptor_with_space_hdr(header, space, i, mtr,
                                                &err, &xdes, init_space);
      if (!descr)
        return err;
    }

    if (xdes != header && !space->full_crc32())
      fil_block_check_type(*xdes, FIL_PAGE_TYPE_XDES, mtr);
    xdes_init(*xdes, descr, mtr);
    const uint16_t xoffset=
      static_cast<uint16_t>(descr - xdes->page.frame + XDES_FLST_NODE);
    if (UNIV_UNLIKELY(init_xdes))
    {
      /* The first page in the extent is a descriptor page and the
      second was reserved for change buffer bitmap: mark them used */
      xdes_set_free<false>(*xdes, descr, 0, mtr);
      xdes_set_free<false>(*xdes, descr, 1, mtr);
      xdes_set_state(*xdes, descr, XDES_FREE_FRAG, mtr);
      if (dberr_t err= flst_add_last(header, FSP_HEADER_OFFSET + FSP_FREE_FRAG,
                                     xdes, xoffset, mtr))
        return err;
      byte *n_used= FSP_HEADER_OFFSET + FSP_FRAG_N_USED + header->page.frame;
      mtr->write<4>(*header, n_used, 2U + mach_read_from_4(n_used));
    }
    else
    {
      if (dberr_t err=
          flst_add_last(header, FSP_HEADER_OFFSET + FSP_FREE,
                        xdes, xoffset, mtr))
        return err;
      count++;
    }
  }

  space->free_len+= count;
  return DB_SUCCESS;
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Allocates a new free extent.
@param[in,out]	space		tablespace
@param[in]	hint		hint of which extent would be desirable: any
page offset in the extent goes; the hint must not be > FSP_FREE_LIMIT
@param[out]	xdes		extent descriptor page
@param[in,out]	mtr		mini-transaction
@return extent descriptor
@retval nullptr if cannot be allocated */
static xdes_t *fsp_alloc_free_extent(fil_space_t *space, uint32_t hint,
                                     buf_block_t **xdes, mtr_t *mtr,
                                     dberr_t *err)
{
	fil_addr_t	first;
	xdes_t*		descr;
	buf_block_t*	desc_block;

	buf_block_t* header = fsp_get_header(space, mtr, err);
	if (!header) {
corrupted:
		space->set_corrupted();
		return nullptr;
	}

	descr = xdes_get_descriptor_with_space_hdr(
		header, space, hint, mtr, err, &desc_block);
	if (!descr) {
		goto corrupted;
	}

	if (desc_block != header && !space->full_crc32()) {
		fil_block_check_type(*desc_block, FIL_PAGE_TYPE_XDES, mtr);
	}

	if (xdes_get_state(descr) == XDES_FREE) {
		/* Ok, we can take this extent */
	} else {
		/* Take the first extent in the free list */
		first = flst_get_first(FSP_HEADER_OFFSET + FSP_FREE
				       + header->page.frame);

		if (first.page == FIL_NULL) {
			*err = fsp_fill_free_list(false, space, header, mtr);
			if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
				goto corrupted;
			}

			first = flst_get_first(FSP_HEADER_OFFSET + FSP_FREE
					       + header->page.frame);
			if (first.page == FIL_NULL) {
				return nullptr;	/* No free extents left */
			}
		}

		descr = xdes_lst_get_descriptor(*space, first, mtr,
						&desc_block, err);
		if (!descr) {
			return descr;
		}
	}

	*err = flst_remove(header, FSP_HEADER_OFFSET + FSP_FREE, desc_block,
			   static_cast<uint16_t>(descr - desc_block->page.frame
						 + XDES_FLST_NODE),
			   mtr);
	if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
		return nullptr;
	}

	space->free_len--;
	*xdes = desc_block;

	return(descr);
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Allocate a single free page.
@param[in,out]	header	tablespace header
@param[in,out]	xdes	extent descriptor page
@param[in,out]	descr	extent descriptor
@param[in]	bit	slot to allocate in the extent
@param[in,out]	mtr	mini-transaction
@return error code */
static dberr_t
fsp_alloc_from_free_frag(buf_block_t *header, buf_block_t *xdes, xdes_t *descr,
			 ulint bit, mtr_t *mtr)
{
  if (UNIV_UNLIKELY(xdes_get_state(descr) != XDES_FREE_FRAG ||
                    !xdes_is_free(descr, bit)))
    return DB_CORRUPTION;
  xdes_set_free<false>(*xdes, descr, bit, mtr);

  /* Update the FRAG_N_USED field */
  byte *n_used_p= FSP_HEADER_OFFSET + FSP_FRAG_N_USED + header->page.frame;
  uint32_t n_used = mach_read_from_4(n_used_p) + 1;

  if (xdes_is_full(descr))
  {
    /* The fragment is full: move it to another list */
    const uint16_t xoffset=
      static_cast<uint16_t>(descr - xdes->page.frame + XDES_FLST_NODE);
    if (dberr_t err= flst_remove(header, FSP_HEADER_OFFSET + FSP_FREE_FRAG,
                                 xdes, xoffset, mtr))
      return err;
    if (dberr_t err= flst_add_last(header, FSP_HEADER_OFFSET + FSP_FULL_FRAG,
                                   xdes, xoffset, mtr))
      return err;
    xdes_set_state(*xdes, descr, XDES_FULL_FRAG, mtr);
    n_used-= FSP_EXTENT_SIZE;
  }

  mtr->write<4>(*header, n_used_p, n_used);
  return DB_SUCCESS;
}

/** Gets a buffer block for an allocated page.
@param[in,out]	space		tablespace
@param[in]	offset		page number of the allocated page
@param[in,out]	mtr		mini-transaction
@return block, initialized */
static buf_block_t* fsp_page_create(fil_space_t *space, uint32_t offset,
                                    mtr_t *mtr)
{
  buf_block_t *free_block= buf_LRU_get_free_block(have_no_mutex),
    *block= buf_page_create(space, offset, space->zip_size(), mtr, free_block);
  if (UNIV_UNLIKELY(block != free_block))
    buf_pool.free_block(free_block);
  fsp_init_file_page(space, block, mtr);
  return block;
}

/** Allocates a single free page from a space.
The page is marked as used.
@param[in,out]	space		tablespace
@param[in]	hint		hint of which page would be desirable
@param[in,out]	mtr		mini-transaction
@param[in,out]	init_mtr	mini-transaction in which the page should be
initialized (may be the same as mtr)
@param[out]	err		error code
@return allocated block
@retval nullptr	if no page could be allocated */
static MY_ATTRIBUTE((warn_unused_result, nonnull))
buf_block_t *fsp_alloc_free_page(fil_space_t *space, uint32_t hint,
                                 mtr_t *mtr, mtr_t *init_mtr, dberr_t *err)
{
  ut_d(space->modify_check(*mtr));
  buf_block_t *block= fsp_get_header(space, mtr, err);
  if (!block)
    return block;

  buf_block_t *xdes;
  /* Get the hinted descriptor */
  xdes_t *descr= xdes_get_descriptor_with_space_hdr(block, space, hint, mtr,
                                                    err, &xdes);
  if (descr && xdes_get_state(descr) == XDES_FREE_FRAG)
    /* Ok, we can take this extent */;
  else if (*err != DB_SUCCESS)
  {
  err_exit:
    space->set_corrupted();
    return nullptr;
  }
  else
  {
    /* Else take the first extent in free_frag list */
    fil_addr_t first = flst_get_first(FSP_HEADER_OFFSET + FSP_FREE_FRAG +
                                      block->page.frame);
    if (first.page == FIL_NULL)
    {
      /* There are no partially full fragments: allocate a free extent
      and add it to the FREE_FRAG list. NOTE that the allocation may
      have as a side-effect that an extent containing a descriptor
      page is added to the FREE_FRAG list. But we will allocate our
      page from the the free extent anyway. */
      descr= fsp_alloc_free_extent(space, hint, &xdes, mtr, err);
      if (!descr)
        return nullptr;
      *err= flst_add_last(block, FSP_HEADER_OFFSET + FSP_FREE_FRAG, xdes,
                          static_cast<uint16_t>(descr - xdes->page.frame +
                                                XDES_FLST_NODE), mtr);
      if (UNIV_UNLIKELY(*err != DB_SUCCESS))
        return nullptr;
      xdes_set_state(*xdes, descr, XDES_FREE_FRAG, mtr);
    }
    else
    {
      descr= xdes_lst_get_descriptor(*space, first, mtr, &xdes, err);
      if (!descr)
        return nullptr;
      /* Reset the hint */
      hint= 0;
    }
  }

  /* Now we have in descr an extent with at least one free page. Look
  for a free page in the extent. */
  uint32_t free= xdes_find_free(descr, hint % FSP_EXTENT_SIZE);
  if (free == FIL_NULL)
  {
  corrupted:
    *err= DB_CORRUPTION;
    goto err_exit;
  }

  uint32_t page_no= xdes_get_offset(descr) + free;
  uint32_t space_size = mach_read_from_4(FSP_HEADER_OFFSET + FSP_SIZE +
                                         block->page.frame);
  ut_ad(space_size == space->size_in_header ||
        (space->id == TRX_SYS_SPACE &&
         srv_startup_is_before_trx_rollback_phase));

  if (space_size <= page_no)
  {
    /* It must be that we are extending a single-table tablespace
    whose size is still < 64 pages */
    ut_ad(!is_system_tablespace(space->id));
    if (page_no >= FSP_EXTENT_SIZE)
    {
      sql_print_error("InnoDB: Trying to extend %s"
                      " by single page(s) though the size is " UINT32PF "."
                      " Page no " UINT32PF ".",
                      space->chain.start->name, space_size, page_no);
      goto corrupted;
    }

    if (!fsp_try_extend_data_file_with_pages(space, page_no, block, mtr))
    {
      *err= DB_OUT_OF_FILE_SPACE;
      return nullptr;
    }
  }

  *err= fsp_alloc_from_free_frag(block, xdes, descr, free, mtr);
  if (UNIV_UNLIKELY(*err != DB_SUCCESS))
    goto corrupted;
  return fsp_page_create(space, page_no, init_mtr);
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Return an extent to the free list of a space.
@param[in,out]  space   tablespace
@param[in]      offset  page number in the extent
@param[in,out]  mtr     mini-transaction
@return error code */
static dberr_t fsp_free_extent(fil_space_t* space, uint32_t offset,
                               mtr_t* mtr)
{
  ut_ad(space->is_owner());
  dberr_t err;
  buf_block_t *block= fsp_get_header(space, mtr, &err);
  if (!block)
    return err;
  buf_block_t *xdes;
  xdes_t *descr= xdes_get_descriptor_with_space_hdr(block, space, offset, mtr,
                                                    &err, &xdes);
  if (!descr)
  {
    ut_ad(err || space->is_stopping());
    return err;
  }

  if (UNIV_UNLIKELY(xdes_get_state(descr) == XDES_FREE))
  {
    space->set_corrupted();
    return DB_CORRUPTION;
  }

  xdes_init(*xdes, descr, mtr);
  space->free_len++;
  return flst_add_last(block, FSP_HEADER_OFFSET + FSP_FREE,
                       xdes, static_cast<uint16_t>(descr - xdes->page.frame +
                                                   XDES_FLST_NODE), mtr);
}

MY_ATTRIBUTE((nonnull))
/** Frees a single page of a space.
The page is marked as free and clean.
@param[in,out]	space		tablespace
@param[in]	offset		page number
@param[in,out]	mtr		mini-transaction
@return error code */
static dberr_t fsp_free_page(fil_space_t *space, uint32_t offset, mtr_t *mtr)
{
	xdes_t*		descr;
	ulint		frag_n_used;

	ut_ad(mtr);
	ut_d(space->modify_check(*mtr));

	/* fprintf(stderr, "Freeing page %lu in space %lu\n", page, space); */

	dberr_t err;
	buf_block_t* header = fsp_get_header(space, mtr, &err);
	if (!header) {
		ut_ad(space->is_stopping());
		return err;
	}
	buf_block_t* xdes;

	descr = xdes_get_descriptor_with_space_hdr(header, space, offset, mtr,
						   &err, &xdes);
	if (!descr) {
		ut_ad(err || space->is_stopping());
		return err;
	}

	const auto state = xdes_get_state(descr);

	switch (state) {
	case XDES_FREE_FRAG:
	case XDES_FULL_FRAG:
		if (!xdes_is_free(descr, offset % FSP_EXTENT_SIZE)) {
			break;
		}
		/* fall through */
	default:
		space->set_corrupted();
		return DB_CORRUPTION;
	}

	frag_n_used = mach_read_from_4(FSP_HEADER_OFFSET + FSP_FRAG_N_USED
				       + header->page.frame);

	const uint16_t xoffset= static_cast<uint16_t>(descr - xdes->page.frame
						      + XDES_FLST_NODE);

	if (state == XDES_FULL_FRAG) {
		/* The fragment was full: move it to another list */
		err = flst_remove(header, FSP_HEADER_OFFSET + FSP_FULL_FRAG,
				  xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
		err = flst_add_last(header, FSP_HEADER_OFFSET + FSP_FREE_FRAG,
				    xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
		xdes_set_state(*xdes, descr, XDES_FREE_FRAG, mtr);
		mtr->write<4>(*header, FSP_HEADER_OFFSET + FSP_FRAG_N_USED
			      + header->page.frame,
			      frag_n_used + FSP_EXTENT_SIZE - 1);
	} else if (UNIV_UNLIKELY(!frag_n_used)) {
		return DB_CORRUPTION;
	} else {
		mtr->write<4>(*header, FSP_HEADER_OFFSET + FSP_FRAG_N_USED
			      + header->page.frame, frag_n_used - 1);
	}

	mtr->free(*space, static_cast<uint32_t>(offset));
	xdes_set_free<true>(*xdes, descr, offset % FSP_EXTENT_SIZE, mtr);
	ut_ad(err == DB_SUCCESS);

	if (!xdes_get_n_used(descr)) {
		/* The extent has become free: move it to another list */
		err = flst_remove(header, FSP_HEADER_OFFSET + FSP_FREE_FRAG,
				  xdes, xoffset, mtr);
		if (err == DB_SUCCESS) {
			err = fsp_free_extent(space, offset, mtr);
		}
	}

	return err;
}

/** @return Number of segment inodes which fit on a single page */
inline ulint FSP_SEG_INODES_PER_PAGE(ulint physical_size)
{
	return (physical_size - FSEG_ARR_OFFSET - 10) / FSEG_INODE_SIZE;
}

/** Returns the nth inode slot on an inode page.
@param[in]	page		segment inode page
@param[in]	i		inode index on page
@return segment inode */
#define fsp_seg_inode_page_get_nth_inode(page, i)	\
	FSEG_ARR_OFFSET + FSEG_INODE_SIZE * i + page

/** Looks for a used segment inode on a segment inode page.
@param page             segment inode page
@param physical_size    page size
@return segment inode index
@retval ULINT_UNDEFINED if not found */
static
ulint
fsp_seg_inode_page_find_used(const page_t *page, ulint physical_size)
{
  for (ulint i= 0; i < FSP_SEG_INODES_PER_PAGE(physical_size); i++)
  {
    const byte *inode= fsp_seg_inode_page_get_nth_inode(page, i);
    if (mach_read_from_8(FSEG_ID + inode))
    {
      ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));
      return i;
    }
  }

  return ULINT_UNDEFINED;
}

/** Looks for an unused segment inode on a segment inode page.
@param[in]	page		segment inode page
@param[in]	i		search forward starting from this index
@param[in]	physical_size	page size
@return segment inode index
@retval ULINT_UNDEFINED if not found */
static
ulint
fsp_seg_inode_page_find_free(const page_t *page, ulint i, ulint physical_size)
{
  for (; i < FSP_SEG_INODES_PER_PAGE(physical_size); i++)
  {
    const byte *inode= fsp_seg_inode_page_get_nth_inode(page, i);
    if (mach_read_from_8(FSEG_ID + inode))
      ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));
    else
      /* This is unused */
      return i;
  }
  return ULINT_UNDEFINED;
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Allocate a file segment inode page.
@param[in,out]  space   tablespace
@param[in,out]  header  tablespace header
@param[in,out]  mtr     mini-transaction
@return error code */
static dberr_t fsp_alloc_seg_inode_page(fil_space_t *space,
                                        buf_block_t *header, mtr_t *mtr)
{
  ut_ad(header->page.id().space() == space->id);
  dberr_t err;
  buf_block_t *block= fsp_alloc_free_page(space, 0, mtr, mtr, &err);

  if (!block)
    return err;

  ut_ad(block->page.lock.not_recursive());

  mtr->write<2>(*block, block->page.frame + FIL_PAGE_TYPE, FIL_PAGE_INODE);

#ifdef UNIV_DEBUG
  const byte *inode= FSEG_ID + FSEG_ARR_OFFSET + block->page.frame;
  for (ulint i= FSP_SEG_INODES_PER_PAGE(space->physical_size()); i--;
       inode += FSEG_INODE_SIZE)
    ut_ad(!mach_read_from_8(inode));
#endif

  return flst_add_last(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE,
                       block, FSEG_INODE_PAGE_NODE, mtr);
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Allocate a file segment inode.
@param[in,out]  space   tablespace
@param[in,out]  header  tablespace header
@param[out]     iblock  segment inode page
@param[in,out]  mtr     mini-transaction
@param[out]     err     error code
@return segment inode
@retval nullptr on failure */
static fseg_inode_t*
fsp_alloc_seg_inode(fil_space_t *space, buf_block_t *header,
                    buf_block_t **iblock, mtr_t *mtr, dberr_t *err)
{
  /* Allocate a new segment inode page if needed. */
  if (!flst_get_len(FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE +
                    header->page.frame))
  {
    *err= fsp_alloc_seg_inode_page(space, header, mtr);
    if (*err != DB_SUCCESS)
      return nullptr;
  }

  const page_id_t page_id
  {
    space->id,
    mach_read_from_4(FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE + FLST_FIRST +
                     FIL_ADDR_PAGE + header->page.frame)
  };

  buf_block_t *block=
    buf_page_get_gen(page_id, space->zip_size(), RW_SX_LATCH,
                     nullptr, BUF_GET_POSSIBLY_FREED, mtr, err);
  if (!block)
    return nullptr;

  if (!space->full_crc32())
    fil_block_check_type(*block, FIL_PAGE_INODE, mtr);

  const ulint physical_size= space->physical_size();
  ulint n= fsp_seg_inode_page_find_free(block->page.frame, 0, physical_size);

  if (UNIV_UNLIKELY(n >= FSP_SEG_INODES_PER_PAGE(physical_size)))
  {
    *err= DB_CORRUPTION;
    return nullptr;
  }
  fseg_inode_t *inode= fsp_seg_inode_page_get_nth_inode(block->page.frame, n);

  if (ULINT_UNDEFINED == fsp_seg_inode_page_find_free(block->page.frame, n + 1,
                                                      physical_size))
  {
    /* There are no other unused headers left on the page: move it
    to another list */
    *err= flst_remove(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE,
                      block, FSEG_INODE_PAGE_NODE, mtr);
    if (UNIV_UNLIKELY(*err != DB_SUCCESS))
      return nullptr;
    *err= flst_add_last(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FULL,
                        block, FSEG_INODE_PAGE_NODE, mtr);
    if (UNIV_UNLIKELY(*err != DB_SUCCESS))
      return nullptr;
  }

  ut_ad(!mach_read_from_8(inode + FSEG_ID) ||
        !memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));
  *iblock= block;
  return inode;
}

MY_ATTRIBUTE((nonnull))
/** Frees a file segment inode.
@param[in,out]	space		tablespace
@param[in,out]	inode		segment inode
@param[in,out]	iblock		segment inode page
@param[in,out]	mtr		mini-transaction */
static void fsp_free_seg_inode(fil_space_t *space, fseg_inode_t *inode,
                               buf_block_t *iblock, mtr_t *mtr)
{
  ut_d(space->modify_check(*mtr));

  dberr_t err;
  buf_block_t *header= fsp_get_header(space, mtr, &err);
  if (!header)
    return;
  if (UNIV_UNLIKELY(memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4)))
  {
    space->set_corrupted();
    return;
  }

  const ulint physical_size= space->physical_size();

  if (ULINT_UNDEFINED == fsp_seg_inode_page_find_free(iblock->page.frame, 0,
                                                      physical_size))
  {
    /* Move the page to another list */
    if (flst_remove(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FULL,
                    iblock, FSEG_INODE_PAGE_NODE, mtr) != DB_SUCCESS)
      return;
    if (flst_add_last(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE,
                      iblock, FSEG_INODE_PAGE_NODE, mtr) != DB_SUCCESS)
      return;
  }

  mtr->memset(iblock, page_offset(inode) + FSEG_ID, FSEG_INODE_SIZE, 0);

  if (ULINT_UNDEFINED != fsp_seg_inode_page_find_used(iblock->page.frame,
                                                      physical_size))
    return;

  /* There are no other used headers left on the page: free it */
  if (flst_remove(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE,
                  iblock, FSEG_INODE_PAGE_NODE, mtr) == DB_SUCCESS)
    fsp_free_page(space, iblock->page.id().page_no(), mtr);
}

MY_ATTRIBUTE((nonnull(1,4,5), warn_unused_result))
/** Returns the file segment inode, page x-latched.
@param[in]	header		segment header
@param[in]	space		space id
@param[in]	zip_size	ROW_FORMAT=COMPRESSED page size, or 0
@param[in,out]	mtr		mini-transaction
@param[out]	block		inode block
@param[out]	err		error code
@return segment inode, page x-latched
@retrval nullptr if the inode is free or corruption was noticed */
static
fseg_inode_t*
fseg_inode_try_get(
	const fseg_header_t*	header,
	uint32_t		space,
	ulint			zip_size,
	mtr_t*			mtr,
	buf_block_t**		block,
        dberr_t*		err = nullptr)
{
  if (UNIV_UNLIKELY(space != mach_read_from_4(header + FSEG_HDR_SPACE)))
  {
  corrupted:
    if (err)
      *err= DB_CORRUPTION;
    return nullptr;
  }

  *block=
    buf_page_get_gen(page_id_t(space,
                               mach_read_from_4(header + FSEG_HDR_PAGE_NO)),
                     zip_size, RW_SX_LATCH, nullptr, BUF_GET_POSSIBLY_FREED,
                     mtr, err);
  if (!*block)
    return nullptr;

  const uint16_t offset= mach_read_from_2(header + FSEG_HDR_OFFSET);
  if (UNIV_UNLIKELY(offset >= (*block)->physical_size()))
    goto corrupted;

  fseg_inode_t *inode= (*block)->page.frame + offset;
  if (UNIV_UNLIKELY(!mach_read_from_8(inode + FSEG_ID) ||
                    memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4)))
    goto corrupted;

  return inode;
}

/** Get the page number from the nth fragment page slot.
@param inode  file segment findex
@param n      slot index
@return page number
@retval FIL_NULL if not in use */
static uint32_t fseg_get_nth_frag_page_no(const fseg_inode_t *inode, ulint n)
{
	ut_ad(inode);
	ut_ad(n < FSEG_FRAG_ARR_N_SLOTS);
	ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));
	return(mach_read_from_4(inode + FSEG_FRAG_ARR
				+ n * FSEG_FRAG_SLOT_SIZE));
}

/** Set the page number in the nth fragment page slot.
@param[in,out]  inode   segment inode
@param[in,out]  iblock  segment inode page
@param[in]      n       slot index
@param[in]      page_no page number to set
@param[in,out]  mtr     mini-transaction */
inline void fseg_set_nth_frag_page_no(fseg_inode_t *inode, buf_block_t *iblock,
                                      ulint n, ulint page_no, mtr_t *mtr)
{
  ut_ad(n < FSEG_FRAG_ARR_N_SLOTS);
  ut_ad(mtr->memo_contains_flagged(iblock, MTR_MEMO_PAGE_SX_FIX));
  ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));

  mtr->write<4>(*iblock, inode + FSEG_FRAG_ARR + n * FSEG_FRAG_SLOT_SIZE,
                page_no);
}

/**********************************************************************//**
Finds a fragment page slot which is free.
@return slot index; ULINT_UNDEFINED if none found */
static
ulint
fseg_find_free_frag_page_slot(
/*==========================*/
	fseg_inode_t*	inode)	/*!< in: segment inode */
{
	ulint	i;
	ulint	page_no;

	for (i = 0; i < FSEG_FRAG_ARR_N_SLOTS; i++) {
		page_no = fseg_get_nth_frag_page_no(inode, i);

		if (page_no == FIL_NULL) {

			return(i);
		}
	}

	return(ULINT_UNDEFINED);
}

/**********************************************************************//**
Finds a fragment page slot which is used and last in the array.
@return slot index; ULINT_UNDEFINED if none found */
static
ulint
fseg_find_last_used_frag_page_slot(
/*===============================*/
	fseg_inode_t*	inode)	/*!< in: segment inode */
{
	ulint	i;
	ulint	page_no;

	for (i = 0; i < FSEG_FRAG_ARR_N_SLOTS; i++) {
		page_no = fseg_get_nth_frag_page_no(
			inode, FSEG_FRAG_ARR_N_SLOTS - i - 1);

		if (page_no != FIL_NULL) {

			return(FSEG_FRAG_ARR_N_SLOTS - i - 1);
		}
	}

	return(ULINT_UNDEFINED);
}

/** Calculate reserved fragment page slots.
@param inode  file segment index
@return number of fragment pages */
static ulint fseg_get_n_frag_pages(const fseg_inode_t *inode)
{
	ulint	i;
	ulint	count	= 0;

	for (i = 0; i < FSEG_FRAG_ARR_N_SLOTS; i++) {
		if (FIL_NULL != fseg_get_nth_frag_page_no(inode, i)) {
			count++;
		}
	}

	return(count);
}

/** Create a new segment.
@param space                tablespace
@param byte_offset          byte offset of the created segment header
@param mtr                  mini-transaction
@param err                  error code
@param has_done_reservation whether fsp_reserve_free_extents() was invoked
@param block                block where segment header is placed,
                            or NULL to allocate an additional page for that
@return the block where the segment header is placed, x-latched
@retval nullptr if could not create segment */
buf_block_t*
fseg_create(fil_space_t *space, ulint byte_offset, mtr_t *mtr, dberr_t *err,
            bool has_done_reservation, buf_block_t *block)
{
	fseg_inode_t*	inode;
	ib_id_t		seg_id;
	uint32_t	n_reserved;
	bool		reserved_extent = false;

	DBUG_ENTER("fseg_create");

	ut_ad(mtr);
	ut_ad(byte_offset >= FIL_PAGE_DATA);
	ut_ad(byte_offset + FSEG_HEADER_SIZE
	      <= srv_page_size - FIL_PAGE_DATA_END);
	buf_block_t* iblock= 0;

	mtr->x_lock_space(space);
	ut_d(space->modify_check(*mtr));

	ut_ad(!block || block->page.id().space() == space->id);

	buf_block_t* header = fsp_get_header(space, mtr, err);
	if (!header) {
		block = nullptr;
		goto funct_exit;
	}

inode_alloc:
	inode = fsp_alloc_seg_inode(space, header, &iblock, mtr, err);

	if (!inode) {
		block = nullptr;
reserve_extent:
		if (!has_done_reservation && !reserved_extent) {
			*err = fsp_reserve_free_extents(&n_reserved, space, 2,
							FSP_NORMAL, mtr);
			if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
				DBUG_RETURN(nullptr);
			}

			/* Extents reserved successfully. So
			try allocating the page or inode */
			reserved_extent = true;
			if (inode) {
				goto page_alloc;
			}

			goto inode_alloc;
		}

		if (inode) {
			fsp_free_seg_inode(space, inode, iblock, mtr);
		}
		goto funct_exit;
	}

	/* Read the next segment id from space header and increment the
	value in space header */

	seg_id = mach_read_from_8(FSP_HEADER_OFFSET + FSP_SEG_ID
				  + header->page.frame);

	mtr->write<8>(*header,
		      FSP_HEADER_OFFSET + FSP_SEG_ID + header->page.frame,
		      seg_id + 1);
	mtr->write<8>(*iblock, inode + FSEG_ID, seg_id);
	ut_ad(!mach_read_from_4(inode + FSEG_NOT_FULL_N_USED));

	flst_init(*iblock, inode + FSEG_FREE, mtr);
	flst_init(*iblock, inode + FSEG_NOT_FULL, mtr);
	flst_init(*iblock, inode + FSEG_FULL, mtr);

	mtr->memcpy(*iblock, inode + FSEG_MAGIC_N, FSEG_MAGIC_N_BYTES, 4);
	compile_time_assert(FSEG_FRAG_SLOT_SIZE == 4);
	compile_time_assert(FIL_NULL == 0xffffffff);
	mtr->memset(iblock,
		    uint16_t(inode - iblock->page.frame) + FSEG_FRAG_ARR,
		    FSEG_FRAG_SLOT_SIZE * FSEG_FRAG_ARR_N_SLOTS, 0xff);

	if (!block) {
page_alloc:
		block = fseg_alloc_free_page_low(space,
						 inode, iblock, 0, FSP_UP,
#ifdef UNIV_DEBUG
						 has_done_reservation,
#endif /* UNIV_DEBUG */
						 mtr, mtr, err);

		if (!block) {
			ut_ad(!has_done_reservation);
			goto reserve_extent;
		}

		ut_d(const auto x = block->page.lock.x_lock_count());
		ut_ad(x || block->page.lock.not_recursive());
		ut_ad(x <= 2);
		ut_ad(!fil_page_get_type(block->page.frame));
		mtr->write<1>(*block, FIL_PAGE_TYPE + 1 + block->page.frame,
			      FIL_PAGE_TYPE_SYS);
	}

	mtr->write<2>(*block, byte_offset + FSEG_HDR_OFFSET
		      + block->page.frame, page_offset(inode));

	mtr->write<4>(*block, byte_offset + FSEG_HDR_PAGE_NO
		      + block->page.frame, iblock->page.id().page_no());

	mtr->write<4,mtr_t::MAYBE_NOP>(*block, byte_offset + FSEG_HDR_SPACE
				       + block->page.frame, space->id);

funct_exit:
	if (!has_done_reservation && reserved_extent) {
		space->release_free_extents(n_reserved);
	}

	DBUG_RETURN(block);
}

/**********************************************************************//**
Calculates the number of pages reserved by a segment, and how many pages are
currently used.
@return number of reserved pages */
static
ulint
fseg_n_reserved_pages_low(
/*======================*/
	const fseg_inode_t*	inode,	/*!< in: segment inode */
	ulint*		used)	/*!< out: number of pages used (not
				more than reserved) */
{
	*used = mach_read_from_4(inode + FSEG_NOT_FULL_N_USED)
		+ FSP_EXTENT_SIZE * flst_get_len(inode + FSEG_FULL)
		+ fseg_get_n_frag_pages(inode);

	return fseg_get_n_frag_pages(inode)
		+ FSP_EXTENT_SIZE * flst_get_len(inode + FSEG_FREE)
		+ FSP_EXTENT_SIZE * flst_get_len(inode + FSEG_NOT_FULL)
		+ FSP_EXTENT_SIZE * flst_get_len(inode + FSEG_FULL);
}

/** Calculate the number of pages reserved by a segment,
and how many pages are currently used.
@param[in]      block   buffer block containing the file segment header
@param[in]      header  file segment header
@param[out]     used    number of pages that are used (not more than reserved)
@param[in,out]  mtr     mini-transaction
@return number of reserved pages */
ulint fseg_n_reserved_pages(const buf_block_t &block,
                            const fseg_header_t *header, ulint *used,
                            mtr_t *mtr)
{
  ut_ad(page_align(header) == block.page.frame);
  buf_block_t *iblock;
  if (fseg_inode_t *inode=
      fseg_inode_try_get(header, block.page.id().space(), block.zip_size(),
                         mtr, &iblock))
    return fseg_n_reserved_pages_low(inode, used);
  return *used= 0;
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Tries to fill the free list of a segment with consecutive free extents.
This happens if the segment is big enough to allow extents in the free list,
the free list is empty, and the extents can be allocated consecutively from
the hint onward.
@param[in]	inode	segment inode
@param[in,out]	iblock	segment inode page
@param[in]	space	tablespace
@param[in]	hint	hint which extent would be good as the first extent
@param[in,out]	mtr	mini-transaction */
static dberr_t fseg_fill_free_list(const fseg_inode_t *inode,
                                   buf_block_t *iblock, fil_space_t *space,
                                   uint32_t hint, mtr_t *mtr)
{
  ulint	used;

  ut_ad(!((page_offset(inode) - FSEG_ARR_OFFSET) % FSEG_INODE_SIZE));
  ut_d(space->modify_check(*mtr));

  if (fseg_n_reserved_pages_low(inode, &used) <
      FSEG_FREE_LIST_LIMIT * FSP_EXTENT_SIZE)
    /* The segment is too small to allow extents in free list */
    return DB_SUCCESS;

  if (UNIV_UNLIKELY(memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4)))
  {
    space->set_corrupted();
    return DB_CORRUPTION;
  }

  if (flst_get_len(inode + FSEG_FREE) > 0)
    /* Free list is not empty */
    return DB_SUCCESS;

  for (ulint i= 0; i < FSEG_FREE_LIST_MAX_LEN; i++, hint += FSP_EXTENT_SIZE)
  {
    buf_block_t *xdes;
    dberr_t err;
    xdes_t *descr= xdes_get_descriptor(space, hint, mtr, &err, &xdes);
    if (!descr || XDES_FREE != xdes_get_state(descr))
      /* We cannot allocate the desired extent: stop */
      return err;

    descr= fsp_alloc_free_extent(space, hint, &xdes, mtr, &err);
    if (UNIV_UNLIKELY(!descr))
      return err;

    if (dberr_t err=
        flst_add_last(iblock,
                      static_cast<uint16_t>(inode - iblock->page.frame +
                                            FSEG_FREE), xdes,
                      static_cast<uint16_t>(descr - xdes->page.frame +
                                            XDES_FLST_NODE), mtr))
      return err;
    xdes_set_state(*xdes, descr, XDES_FSEG, mtr);
    mtr->memcpy(*xdes, descr + XDES_ID, inode + FSEG_ID, 8);
  }

  return DB_SUCCESS;
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Allocates a free extent for the segment: looks first in the free list of
the segment, then tries to allocate from the space free list.
NOTE that the extent returned still resides in the segment free list, it is
not yet taken off it!
@param[in]	inode		segment inode
@param[in,out]	iblock		segment inode page
@param[out]	xdes		extent descriptor page
@param[in,out]	space		tablespace
@param[in,out]	mtr		mini-transaction
@param[out]	err		error code
@retval nullptr	if no page could be allocated */
static
xdes_t*
fseg_alloc_free_extent(
	const fseg_inode_t*	inode,
	buf_block_t*		iblock,
	buf_block_t**		xdes,
	fil_space_t*		space,
	mtr_t*			mtr,
	dberr_t*		err)
{
  ut_ad(!((page_offset(inode) - FSEG_ARR_OFFSET) % FSEG_INODE_SIZE));
  ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));
  ut_d(space->modify_check(*mtr));

  if (flst_get_len(inode + FSEG_FREE))
  {
    /* Segment free list is not empty, allocate from it */
    return xdes_lst_get_descriptor(*space, flst_get_first(inode + FSEG_FREE),
                                   mtr, xdes, err);
  }

  xdes_t* descr= fsp_alloc_free_extent(space, 0, xdes, mtr, err);
  if (UNIV_UNLIKELY(!descr))
    return descr;
  xdes_set_state(**xdes, descr, XDES_FSEG, mtr);
  mtr->memcpy<mtr_t::MAYBE_NOP>(**xdes, descr + XDES_ID, inode + FSEG_ID, 8);
  *err= flst_add_last(iblock,
                      static_cast<uint16_t>(inode - iblock->page.frame +
                                            FSEG_FREE), *xdes,
                      static_cast<uint16_t>(descr - (*xdes)->page.frame +
                                            XDES_FLST_NODE), mtr);
  if (UNIV_LIKELY(*err != DB_SUCCESS))
    return nullptr;
  /* Try to fill the segment free list */
  *err= fseg_fill_free_list(inode, iblock, space,
                            xdes_get_offset(descr) + FSP_EXTENT_SIZE, mtr);
  if (UNIV_UNLIKELY(*err != DB_SUCCESS))
    return nullptr;

  return descr;
}

/** Allocates a single free page from a segment.
This function implements the intelligent allocation strategy which tries to
minimize file space fragmentation.
@param[in,out]	space			tablespace
@param[in,out]	seg_inode		segment inode
@param[in,out]	iblock			segment inode page
@param[in]	hint			hint of which page would be desirable
@param[in]	direction		if the new page is needed because of
an index page split, and records are inserted there in order, into which
direction they go alphabetically: FSP_DOWN, FSP_UP, FSP_NO_DIR
@param[in,out]	mtr			mini-transaction
@param[in,out]	init_mtr		mtr or another mini-transaction in
which the page should be initialized.
@param[out]	err			error code
@return the allocated page
@retval nullptr	if no page could be allocated */
static
buf_block_t*
fseg_alloc_free_page_low(
	fil_space_t*		space,
	fseg_inode_t*		seg_inode,
	buf_block_t*		iblock,
	uint32_t		hint,
	byte			direction,
#ifdef UNIV_DEBUG
	bool			has_done_reservation,
	/*!< whether the space has already been reserved */
#endif /* UNIV_DEBUG */
	mtr_t*			mtr,
	mtr_t*			init_mtr,
	dberr_t*		err)
{
	ib_id_t		seg_id;
	ulint		used;
	ulint		reserved;
	xdes_t*		descr;		/*!< extent of the hinted page */
	uint32_t	ret_page;	/*!< the allocated page offset, FIL_NULL
					if could not be allocated */
	xdes_t*		ret_descr;	/*!< the extent of the allocated page */
	buf_block_t*	xdes;
	ulint		n;

	ut_ad((direction >= FSP_UP) && (direction <= FSP_NO_DIR));
	ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + seg_inode, 4));
	ut_ad(!((page_offset(seg_inode) - FSEG_ARR_OFFSET) % FSEG_INODE_SIZE));
	seg_id = mach_read_from_8(seg_inode + FSEG_ID);

	ut_ad(seg_id);
	ut_d(space->modify_check(*mtr));
	ut_ad(fil_page_get_type(page_align(seg_inode)) == FIL_PAGE_INODE);

	reserved = fseg_n_reserved_pages_low(seg_inode, &used);

	buf_block_t* header = fsp_get_header(space, mtr, err);
	if (!header) {
		return header;
	}

	descr = xdes_get_descriptor_with_space_hdr(header, space, hint, mtr,
						   err, &xdes);
	if (!descr) {
		if (*err != DB_SUCCESS) {
			return nullptr;
		}
		/* Hint outside space or too high above free limit: reset
		hint */
		/* The file space header page is always allocated. */
		hint = 0;
		descr = xdes_get_descriptor(space, hint, mtr, err, &xdes);
		if (!descr) {
			return nullptr;
		}
	}

	/* In the big if-else below we look for ret_page and ret_descr */
	/*-------------------------------------------------------------*/
	if ((xdes_get_state(descr) == XDES_FSEG)
	    && mach_read_from_8(descr + XDES_ID) == seg_id
	    && xdes_is_free(descr, hint % FSP_EXTENT_SIZE)) {
take_hinted_page:
		/* 1. We can take the hinted page
		=================================*/
		ret_descr = descr;
		ret_page = hint;
		/* Skip the check for extending the tablespace. If the
		page hint were not within the size of the tablespace,
		we would have got (descr == NULL) above and reset the hint. */
		goto got_hinted_page;
		/*-----------------------------------------------------------*/
	} else if (xdes_get_state(descr) == XDES_FREE
		   && reserved - used < reserved / FSEG_FILLFACTOR
		   && used >= FSEG_FRAG_LIMIT) {

		/* 2. We allocate the free extent from space and can take
		=========================================================
		the hinted page
		===============*/
		ret_descr = fsp_alloc_free_extent(space, hint, &xdes,
						  mtr, err);

		if (UNIV_UNLIKELY(ret_descr != descr)) {
			if (*err != DB_SUCCESS) {
				*err = DB_CORRUPTION;
			}
			return nullptr;
		}

		xdes_set_state(*xdes, ret_descr, XDES_FSEG, mtr);
		mtr->write<8,mtr_t::MAYBE_NOP>(*xdes, ret_descr + XDES_ID,
					       seg_id);
		*err = flst_add_last(
			iblock,
			static_cast<uint16_t>(seg_inode - iblock->page.frame
					      + FSEG_FREE), xdes,
			static_cast<uint16_t>(ret_descr
					      - xdes->page.frame
					      + XDES_FLST_NODE), mtr);
		if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
			return nullptr;
		}

		/* Try to fill the segment free list */
		*err = fseg_fill_free_list(seg_inode, iblock, space,
					   hint + FSP_EXTENT_SIZE, mtr);
		if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
			return nullptr;
		}
		goto take_hinted_page;
		/*-----------------------------------------------------------*/
	} else if ((direction != FSP_NO_DIR)
		   && ((reserved - used) < reserved / FSEG_FILLFACTOR)
		   && (used >= FSEG_FRAG_LIMIT)
		   && (ret_descr = fseg_alloc_free_extent(seg_inode, iblock,
							  &xdes, space,
							  mtr, err))) {
		/* 3. We take any free extent (which was already assigned above
		===============================================================
		in the if-condition to ret_descr) and take the lowest or
		========================================================
		highest page in it, depending on the direction
		==============================================*/
		ret_page = xdes_get_offset(ret_descr);

		if (direction == FSP_DOWN) {
			ret_page += FSP_EXTENT_SIZE - 1;
		}
		ut_ad(!has_done_reservation || ret_page != FIL_NULL);
		/*-----------------------------------------------------------*/
	} else if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
		return nullptr;
	} else if ((xdes_get_state(descr) == XDES_FSEG)
		   && mach_read_from_8(descr + XDES_ID) == seg_id
		   && (!xdes_is_full(descr))) {

		/* 4. We can take the page from the same extent as the
		======================================================
		hinted page (and the extent already belongs to the
		==================================================
		segment)
		========*/
		ret_descr = descr;
		ret_page = xdes_find_free(ret_descr, hint % FSP_EXTENT_SIZE);
		if (ret_page == FIL_NULL) {
			ut_ad(!has_done_reservation);
		} else {
			ret_page += xdes_get_offset(ret_descr);
		}
		/*-----------------------------------------------------------*/
	} else if (reserved - used > 0) {
		/* 5. We take any unused page from the segment
		==============================================*/
		fil_addr_t	first;

		if (flst_get_len(seg_inode + FSEG_NOT_FULL) > 0) {
			first = flst_get_first(seg_inode + FSEG_NOT_FULL);
		} else if (flst_get_len(seg_inode + FSEG_FREE) > 0) {
			first = flst_get_first(seg_inode + FSEG_FREE);
		} else {
			ut_ad(!has_done_reservation);
			return(NULL);
		}

		ret_descr = xdes_lst_get_descriptor(*space, first, mtr, &xdes);
		if (!ret_descr) {
			return nullptr;
		}

		ret_page = xdes_find_free(ret_descr);
		if (ret_page == FIL_NULL) {
			ut_ad(!has_done_reservation);
		} else {
			ret_page += xdes_get_offset(ret_descr);
		}
		/*-----------------------------------------------------------*/
	} else if (used < FSEG_FRAG_LIMIT) {
		/* 6. We allocate an individual page from the space
		===================================================*/
		buf_block_t* block = fsp_alloc_free_page(
			space, hint, mtr, init_mtr, err);

		ut_ad(block || !has_done_reservation || *err);

		if (block) {
			/* Put the page in the fragment page array of the
			segment */
			n = fseg_find_free_frag_page_slot(seg_inode);
			if (UNIV_UNLIKELY(n == ULINT_UNDEFINED)) {
				*err = DB_CORRUPTION;
				return nullptr;
			}

			fseg_set_nth_frag_page_no(
				seg_inode, iblock, n,
				block->page.id().page_no(), mtr);
		}

		/* fsp_alloc_free_page() invoked fsp_init_file_page()
		already. */
		return(block);
		/*-----------------------------------------------------------*/
	} else {
		/* 7. We allocate a new extent and take its first page
		======================================================*/
		ret_descr = fseg_alloc_free_extent(seg_inode, iblock, &xdes,
						   space, mtr, err);

		if (!ret_descr) {
			ut_ad(!has_done_reservation || *err);
			return nullptr;
		} else {
			ret_page = xdes_get_offset(ret_descr);
		}
	}

	if (ret_page == FIL_NULL) {
		/* Page could not be allocated */

		ut_ad(!has_done_reservation);
		return(NULL);
	}

	if (space->size <= ret_page && !is_predefined_tablespace(space->id)) {
		/* It must be that we are extending a single-table
		tablespace whose size is still < 64 pages */

		if (ret_page >= FSP_EXTENT_SIZE) {
			sql_print_error("InnoDB: Trying to extend '%s'"
					" by single page(s) though the"
					" space size " UINT32PF "."
					" Page no " UINT32PF ".",
					space->chain.start->name, space->size,
					ret_page);
			ut_ad(!has_done_reservation);
			return(NULL);
		}

		if (!fsp_try_extend_data_file_with_pages(
			    space, ret_page, header, mtr)) {
			/* No disk space left */
			ut_ad(!has_done_reservation);
			return(NULL);
		}
	}

got_hinted_page:
	/* ret_descr == NULL if the block was allocated from free_frag
	(XDES_FREE_FRAG) */
	if (ret_descr != NULL) {
		/* At this point we know the extent and the page offset.
		The extent is still in the appropriate list (FSEG_NOT_FULL
		or FSEG_FREE), and the page is not yet marked as used. */

		ut_d(buf_block_t* xxdes);
		ut_ad(xdes_get_descriptor(space, ret_page, mtr, err, &xxdes)
		      == ret_descr);
		ut_ad(xdes == xxdes);
		ut_ad(xdes_is_free(ret_descr, ret_page % FSP_EXTENT_SIZE));

		*err = fseg_mark_page_used(seg_inode, iblock, ret_page,
                                           ret_descr, xdes, mtr);
		if (UNIV_UNLIKELY(*err != DB_SUCCESS)) {
			return nullptr;
		}
	}

	return fsp_page_create(space, ret_page, init_mtr);
}

/**********************************************************************//**
Allocates a single free page from a segment. This function implements
the intelligent allocation strategy which tries to minimize file space
fragmentation.
@retval NULL if no page could be allocated */
buf_block_t*
fseg_alloc_free_page_general(
/*=========================*/
	fseg_header_t*	seg_header,/*!< in/out: segment header */
	uint32_t	hint,	/*!< in: hint of which page would be
				desirable */
	byte		direction,/*!< in: if the new page is needed because
				of an index page split, and records are
				inserted there in order, into which
				direction they go alphabetically: FSP_DOWN,
				FSP_UP, FSP_NO_DIR */
	bool		has_done_reservation, /*!< in: true if the caller has
				already done the reservation for the page
				with fsp_reserve_free_extents, then there
				is no need to do the check for this individual
				page */
	mtr_t*		mtr,	/*!< in/out: mini-transaction */
	mtr_t*		init_mtr,/*!< in/out: mtr or another mini-transaction
				in which the page should be initialized. */
	dberr_t*	err)	/*!< out: error code */
{
	fseg_inode_t*	inode;
	fil_space_t*	space;
	buf_block_t*	iblock;
	buf_block_t*	block;
	uint32_t	n_reserved;

	const uint32_t space_id = page_get_space_id(page_align(seg_header));
	space = mtr->x_lock_space(space_id);
	inode = fseg_inode_try_get(seg_header, space_id, space->zip_size(),
				   mtr, &iblock, err);
	if (!inode) {
		return nullptr;
	}
	if (!space->full_crc32()) {
		fil_block_check_type(*iblock, FIL_PAGE_INODE, mtr);
	}

	if (!has_done_reservation) {
		*err = fsp_reserve_free_extents(&n_reserved, space, 2,
						FSP_NORMAL, mtr);
		if (*err != DB_SUCCESS) {
			return nullptr;
		}
	}

	block = fseg_alloc_free_page_low(space,
					 inode, iblock, hint, direction,
#ifdef UNIV_DEBUG
					 has_done_reservation,
#endif /* UNIV_DEBUG */
					 mtr, init_mtr, err);

	/* The allocation cannot fail if we have already reserved a
	space for the page. */
	ut_ad(block || !has_done_reservation || *err);

	if (!has_done_reservation) {
		space->release_free_extents(n_reserved);
	}

	return(block);
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Check that we have at least n_pages frag pages free in the first extent
of a single-table tablespace, and they are also physically initialized to
the data file. That is we have already extended the data file so that those
pages are inside the data file. If not, this function extends the tablespace
with pages.
@param[in,out]	space	tablespace
@param[in,out]	header	tablespace header, x-latched
@param[in]	size	tablespace size in pages, less than FSP_EXTENT_SIZE
@param[in,out]	mtr	mini-transaction
@param[in]	n_pages	number of pages to reserve
@return error code */
static
dberr_t
fsp_reserve_free_pages(
	fil_space_t*	space,
	buf_block_t*	header,
	ulint		size,
	mtr_t*		mtr,
	uint32_t	n_pages)
{
  ut_ad(space != fil_system.sys_space && space != fil_system.temp_space);
  ut_ad(size < FSP_EXTENT_SIZE);

  dberr_t err= DB_OUT_OF_FILE_SPACE;
  const xdes_t *descr=
    xdes_get_descriptor_with_space_hdr(header, space, 0, mtr, &err);
  if (!descr)
    return err;
  const uint32_t n_used= xdes_get_n_used(descr);
  if (size >= n_used + n_pages)
    return DB_SUCCESS;
  if (n_used > size)
    return DB_CORRUPTION;
  return fsp_try_extend_data_file_with_pages(space, n_used + n_pages - 1,
                                             header, mtr)
    ? DB_SUCCESS
    : DB_OUT_OF_FILE_SPACE;
}

/** Reserves free pages from a tablespace. All mini-transactions which may
use several pages from the tablespace should call this function beforehand
and reserve enough free extents so that they certainly will be able
to do their operation, like a B-tree page split, fully. Reservations
must be released with function fil_space_t::release_free_extents()!

The alloc_type below has the following meaning: FSP_NORMAL means an
operation which will probably result in more space usage, like an
insert in a B-tree; FSP_UNDO means allocation to undo logs: if we are
deleting rows, then this allocation will in the long run result in
less space usage (after a purge); FSP_CLEANING means allocation done
in a physical record delete (like in a purge) or other cleaning operation
which will result in less space usage in the long run. We prefer the latter
two types of allocation: when space is scarce, FSP_NORMAL allocations
will not succeed, but the latter two allocations will succeed, if possible.
The purpose is to avoid dead end where the database is full but the
user cannot free any space because these freeing operations temporarily
reserve some space.

Single-table tablespaces whose size is < FSP_EXTENT_SIZE pages are a special
case. In this function we would liberally reserve several extents for
every page split or merge in a B-tree. But we do not want to waste disk space
if the table only occupies < FSP_EXTENT_SIZE pages. That is why we apply
different rules in that special case, just ensuring that there are n_pages
free pages available.

@param[out]	n_reserved	number of extents actually reserved; if we
				return true and the tablespace size is <
				FSP_EXTENT_SIZE pages, then this can be 0,
				otherwise it is n_ext
@param[in,out]	space		tablespace
@param[in]	n_ext		number of extents to reserve
@param[in]	alloc_type	page reservation type (FSP_BLOB, etc)
@param[in,out]	mtr		the mini transaction
@param[in]	n_pages		for small tablespaces (tablespace size is
				less than FSP_EXTENT_SIZE), number of free
				pages to reserve.
@return error code
@retval DB_SUCCESS if we were able to make the reservation */
dberr_t
fsp_reserve_free_extents(
	uint32_t*	n_reserved,
	fil_space_t*	space,
	uint32_t	n_ext,
	fsp_reserve_t	alloc_type,
	mtr_t*		mtr,
	uint32_t	n_pages)
{
	ulint		reserve;

	ut_ad(mtr);
	*n_reserved = n_ext;

	const uint32_t extent_size = FSP_EXTENT_SIZE;

	mtr->x_lock_space(space);
	const unsigned physical_size = space->physical_size();

	dberr_t err;
	buf_block_t* header = fsp_get_header(space, mtr, &err);
	if (!header) {
		return err;
	}
try_again:
	uint32_t size = mach_read_from_4(FSP_HEADER_OFFSET + FSP_SIZE
					 + header->page.frame);
	ut_ad(size == space->size_in_header);

	if (size < extent_size && n_pages < extent_size / 2) {
		/* Use different rules for small single-table tablespaces */
		*n_reserved = 0;
		return fsp_reserve_free_pages(space, header, size,
					      mtr, n_pages);
	}

	uint32_t n_free_list_ext = flst_get_len(FSP_HEADER_OFFSET + FSP_FREE
						+ header->page.frame);
	ut_ad(space->free_len == n_free_list_ext);

	uint32_t free_limit = mach_read_from_4(FSP_HEADER_OFFSET
					       + FSP_FREE_LIMIT
					       + header->page.frame);
	ut_ad(space->free_limit == free_limit);

	/* Below we play safe when counting free extents above the free limit:
	some of them will contain extent descriptor pages, and therefore
	will not be free extents */

	uint32_t n_free_up;

	if (size >= free_limit) {
		n_free_up = (size - free_limit) / extent_size;
		if (n_free_up) {
			n_free_up--;
			n_free_up -= n_free_up / (physical_size / extent_size);
		}
	} else {
		ut_ad(alloc_type == FSP_BLOB);
		n_free_up = 0;
	}

	uint32_t n_free = n_free_list_ext + n_free_up;

	switch (alloc_type) {
	case FSP_NORMAL:
		/* We reserve 1 extent + 0.5 % of the space size to undo logs
		and 1 extent + 0.5 % to cleaning operations; NOTE: this source
		code is duplicated in the function below! */

		reserve = 2 + ((size / extent_size) * 2) / 200;

		if (n_free <= reserve + n_ext) {

			goto try_to_extend;
		}
		break;
	case FSP_UNDO:
		/* We reserve 0.5 % of the space size to cleaning operations */

		reserve = 1 + ((size / extent_size) * 1) / 200;

		if (n_free <= reserve + n_ext) {

			goto try_to_extend;
		}
		break;
	case FSP_CLEANING:
	case FSP_BLOB:
		reserve = 0;
		break;
	default:
		ut_error;
	}

	if (space->reserve_free_extents(n_free, n_ext)) {
		return DB_SUCCESS;
	}
try_to_extend:
	if (fsp_try_extend_data_file(space, header, mtr)) {
		goto try_again;
	}

	return DB_OUT_OF_FILE_SPACE;
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Frees a single page of a segment.
@param[in]	seg_inode	segment inode
@param[in,out]	space		tablespace
@param[in]	offset		page number
@param[in,out]	mtr		mini-transaction
@param[in]	ahi		Drop adaptive hash index
@return error code */
static
dberr_t
fseg_free_page_low(
	fseg_inode_t*		seg_inode,
	buf_block_t*		iblock,
	fil_space_t*		space,
	uint32_t		offset,
	mtr_t*			mtr
#ifdef BTR_CUR_HASH_ADAPT
	,bool			ahi=false
#endif /* BTR_CUR_HASH_ADAPT */
	)
{
	ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + seg_inode, 4));
	ut_ad(!((page_offset(seg_inode) - FSEG_ARR_OFFSET) % FSEG_INODE_SIZE));
	ut_ad(iblock->page.frame == page_align(seg_inode));
	ut_d(space->modify_check(*mtr));

#ifdef BTR_CUR_HASH_ADAPT
	if (ahi) {
		btr_search_drop_page_hash_when_freed(
			page_id_t(space->id, offset));
	}
#endif /* BTR_CUR_HASH_ADAPT */

	const uint32_t extent_size = FSP_EXTENT_SIZE;
	ut_ad(ut_is_2pow(extent_size));
	buf_block_t* xdes;
	dberr_t err;
	xdes_t* descr = xdes_get_descriptor(space, offset, mtr, &err, &xdes);

	if (!descr) {
		return err;
	}
	if (UNIV_UNLIKELY(xdes_is_free(descr, offset & (extent_size - 1)))) {
corrupted:
		space->set_corrupted();
		return DB_CORRUPTION;
	}

	if (xdes_get_state(descr) != XDES_FSEG) {
		/* The page is in the fragment pages of the segment */
		for (ulint i = 0;; i++) {
			if (fseg_get_nth_frag_page_no(seg_inode, i)
			    != offset) {
				continue;
			}

			compile_time_assert(FIL_NULL == 0xffffffff);
			mtr->memset(iblock, uint16_t(seg_inode
						     - iblock->page.frame)
				    + FSEG_FRAG_ARR
				    + i * FSEG_FRAG_SLOT_SIZE, 4, 0xff);
			break;
		}

		return fsp_free_page(space, offset, mtr);
	}

	/* If we get here, the page is in some extent of the segment */

	if (UNIV_UNLIKELY(memcmp(descr + XDES_ID, seg_inode + FSEG_ID, 8))) {
		goto corrupted;
	}

	byte* p_not_full = seg_inode + FSEG_NOT_FULL_N_USED;
	uint32_t not_full_n_used = mach_read_from_4(p_not_full);
	const uint16_t xoffset= uint16_t(descr - xdes->page.frame
					 + XDES_FLST_NODE);
	const uint16_t ioffset= uint16_t(seg_inode - iblock->page.frame);

	if (xdes_is_full(descr)) {
		/* The fragment is full: move it to another list */
		err = flst_remove(iblock,
				  static_cast<uint16_t>(FSEG_FULL + ioffset),
				  xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
		err = flst_add_last(iblock, static_cast<uint16_t>(FSEG_NOT_FULL
								  + ioffset),
				    xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
		not_full_n_used += extent_size - 1;
	} else {
		if (!not_full_n_used) {
			goto corrupted;
		}
		not_full_n_used--;
	}

	mtr->write<4>(*iblock, p_not_full, not_full_n_used);
	xdes_set_free<true>(*xdes, descr, offset & (extent_size - 1), mtr);

	if (!xdes_get_n_used(descr)) {
		err = flst_remove(iblock, static_cast<uint16_t>(FSEG_NOT_FULL
								+ ioffset),
				  xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
		err = fsp_free_extent(space, offset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
	}

	mtr->free(*space, static_cast<uint32_t>(offset));
	return DB_SUCCESS;
}

/** Free a page in a file segment.
@param[in,out]	seg_header	file segment header
@param[in,out]	space		tablespace
@param[in]	offset		page number
@param[in,out]	mtr		mini-transaction
@param[in]	have_latch	whether space->x_lock() was already called
@return error code */
dberr_t fseg_free_page(fseg_header_t *seg_header, fil_space_t *space,
                       uint32_t offset, mtr_t *mtr, bool have_latch)
{
  buf_block_t *iblock;
  if (have_latch)
    ut_ad(space->is_owner());
  else
    mtr->x_lock_space(space);

  DBUG_PRINT("fseg_free_page",
             ("space_id: " ULINTPF ", page_no: %u", space->id, offset));

  dberr_t err;
  if (fseg_inode_t *seg_inode= fseg_inode_try_get(seg_header,
                                                  space->id, space->zip_size(),
                                                  mtr, &iblock, &err))
  {
    if (!space->full_crc32())
      fil_block_check_type(*iblock, FIL_PAGE_INODE, mtr);
    return fseg_free_page_low(seg_inode, iblock, space, offset, mtr);
  }

  return err;
}

/** Determine whether a page is allocated.
@param space   tablespace
@param page    page number
@return error code
@retval DB_SUCCESS             if the page is marked as free
@retval DB_SUCCESS_LOCKED_REC  if the page is marked as allocated */
dberr_t fseg_page_is_allocated(fil_space_t *space, unsigned page)
{
  mtr_t mtr;
  uint32_t dpage= xdes_calc_descriptor_page(space->zip_size(), page);
  const unsigned zip_size= space->zip_size();
  dberr_t err= DB_SUCCESS;

  mtr.start();
  if (!space->is_owner())
    mtr.x_lock_space(space);

  if (page >= space->free_limit || page >= space->size_in_header);
  else if (const buf_block_t *b=
           buf_page_get_gen(page_id_t(space->id, dpage), space->zip_size(),
                            RW_S_LATCH, nullptr, BUF_GET_POSSIBLY_FREED,
                            &mtr, &err))
  {
    if (!dpage &&
        (space->free_limit !=
         mach_read_from_4(FSP_FREE_LIMIT + FSP_HEADER_OFFSET +
                          b->page.frame) ||
         space->size_in_header !=
         mach_read_from_4(FSP_SIZE + FSP_HEADER_OFFSET + b->page.frame)))
      err= DB_CORRUPTION;
    else
      err= xdes_is_free(b->page.frame + XDES_ARR_OFFSET + XDES_SIZE
                        * xdes_calc_descriptor_index(zip_size, page),
                        page & (FSP_EXTENT_SIZE - 1))
        ? DB_SUCCESS
        : DB_SUCCESS_LOCKED_REC;
  }

  mtr.commit();
  return err;
}

MY_ATTRIBUTE((nonnull, warn_unused_result))
/** Free an extent of a segment to the space free list.
@param[in,out]	seg_inode	segment inode
@param[in,out]	space		tablespace
@param[in]	page		page number in the extent
@param[in,out]	mtr		mini-transaction
@return error code */
static
dberr_t
fseg_free_extent(
	fseg_inode_t*		seg_inode,
	buf_block_t*		iblock,
	fil_space_t*		space,
	uint32_t		page,
	mtr_t*			mtr
#ifdef BTR_CUR_HASH_ADAPT
	,bool			ahi=false
#endif /* BTR_CUR_HASH_ADAPT */
	)
{
	buf_block_t* xdes;
	dberr_t err;
	xdes_t*	descr = xdes_get_descriptor(space, page, mtr, &err, &xdes);

	if (!descr) {
		return err;
	}

	if (UNIV_UNLIKELY(xdes_get_state(descr) != XDES_FSEG
			  || memcmp(descr + XDES_ID, seg_inode + FSEG_ID, 8)
			  || memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N
				    + seg_inode, 4))) {
		return DB_CORRUPTION;
	}
	ut_d(space->modify_check(*mtr));
	const uint32_t first_page_in_extent = page - (page % FSP_EXTENT_SIZE);

	const uint16_t xoffset= uint16_t(descr - xdes->page.frame
					 + XDES_FLST_NODE);
	const uint16_t ioffset= uint16_t(seg_inode - iblock->page.frame);

#ifdef BTR_CUR_HASH_ADAPT
	if (ahi) {
		for (uint32_t i = 0; i < FSP_EXTENT_SIZE; i++) {
			if (!xdes_is_free(descr, i)) {
				/* Drop search system page hash index
				if the page is found in the pool and
				is hashed */
				btr_search_drop_page_hash_when_freed(
					page_id_t(space->id,
						 first_page_in_extent + i));
			}
		}
	}
#endif /* BTR_CUR_HASH_ADAPT */

	uint16_t lst;

	if (xdes_is_full(descr)) {
		lst = static_cast<uint16_t>(FSEG_FULL + ioffset);
remove:
		err = flst_remove(iblock, lst, xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
	} else if (!xdes_get_n_used(descr)) {
		lst = static_cast<uint16_t>(FSEG_FREE + ioffset);
                goto remove;
	} else {
		err = flst_remove(
			iblock, static_cast<uint16_t>(FSEG_NOT_FULL + ioffset),
			xdes, xoffset, mtr);
		if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
			return err;
		}
		uint32_t not_full_n_used = mach_read_from_4(
			FSEG_NOT_FULL_N_USED + seg_inode);
		uint32_t descr_n_used = xdes_get_n_used(descr);
		if (not_full_n_used < descr_n_used) {
			return DB_CORRUPTION;
		}
		mtr->write<4>(*iblock, seg_inode + FSEG_NOT_FULL_N_USED,
			      not_full_n_used - descr_n_used);
	}

	std::vector<uint8_t> going_to_free;
	static_assert(FSP_EXTENT_SIZE_MIN == 256, "compatibility");
	static_assert(FSP_EXTENT_SIZE_MAX == 64, "compatibility");

	for (uint32_t i = 0; i < FSP_EXTENT_SIZE; i++) {
		if (!xdes_is_free(descr, i)) {
			going_to_free.emplace_back(uint8_t(i));
		}
	}

	if (dberr_t err = fsp_free_extent(space, page, mtr)) {
		return err;
	}

	for (uint32_t i : going_to_free) {
		mtr->free(*space, first_page_in_extent + i);
		buf_page_free(space, first_page_in_extent + i, mtr);
	}

	return DB_SUCCESS;
}

/** Frees part of a segment. This function can be used to free
a segment by repeatedly calling this function in different
mini-transactions. Doing the freeing in a single mini-transaction
might result in too big a mini-transaction.
@param	header	segment header; NOTE: if the header resides on first
		page of the frag list of the segment, this pointer
		becomes obsolete after the last freeing step
@param	mtr	mini-transaction
@param	ahi	Drop the adaptive hash index
@return whether the freeing was completed */
bool
fseg_free_step(
	fseg_header_t*	header,
	mtr_t*		mtr
#ifdef BTR_CUR_HASH_ADAPT
	,bool		ahi
#endif /* BTR_CUR_HASH_ADAPT */
	)
{
	ulint		n;
	fseg_inode_t*	inode;

	const uint32_t space_id = page_get_space_id(page_align(header));
	const uint32_t header_page = page_get_page_no(page_align(header));

	fil_space_t* space = mtr->x_lock_space(space_id);
	xdes_t* descr = xdes_get_descriptor(space, header_page, mtr);

	if (!descr) {
		return true;
	}

	/* Check that the header resides on a page which has not been
	freed yet */

	if (UNIV_UNLIKELY(xdes_is_free(descr,
				       header_page & (FSP_EXTENT_SIZE - 1)))) {
		/* Some corruption was detected: stop the freeing
		in order to prevent a crash. */
		return true;
	}
	buf_block_t* iblock;
	const ulint zip_size = space->zip_size();
	inode = fseg_inode_try_get(header, space_id, zip_size, mtr, &iblock);
	if (!inode || space->is_stopping()) {
		return true;
	}

	if (!space->full_crc32()) {
		fil_block_check_type(*iblock, FIL_PAGE_INODE, mtr);
	}

	dberr_t err;
	descr = fseg_get_first_extent(inode, space, mtr, &err);

	if (descr) {
		/* Free the extent held by the segment */
		return fseg_free_extent(inode, iblock, space,
					xdes_get_offset(descr), mtr
#ifdef BTR_CUR_HASH_ADAPT
					, ahi
#endif /* BTR_CUR_HASH_ADAPT */
					) != DB_SUCCESS;
	}

	if (err != DB_SUCCESS || space->is_stopping()) {
		return true;
	}

	/* Free a frag page */
	n = fseg_find_last_used_frag_page_slot(inode);

	if (n == ULINT_UNDEFINED) {
		/* Freeing completed: free the segment inode */
		fsp_free_seg_inode(space, inode, iblock, mtr);
		return true;
	}

	uint32_t page_no = fseg_get_nth_frag_page_no(inode, n);

	if (fseg_free_page_low(inode, iblock, space, page_no, mtr
#ifdef BTR_CUR_HASH_ADAPT
			       , ahi
#endif /* BTR_CUR_HASH_ADAPT */
			       ) != DB_SUCCESS) {
		return true;
	}

	buf_page_free(space, page_no, mtr);

	n = fseg_find_last_used_frag_page_slot(inode);

	if (n == ULINT_UNDEFINED) {
		/* Freeing completed: free the segment inode */
		fsp_free_seg_inode(space, inode, iblock, mtr);

		return true;
	}

	return false;
}

bool
fseg_free_step_not_header(
	fseg_header_t*	header,
	mtr_t*		mtr
#ifdef BTR_CUR_HASH_ADAPT
	,bool		ahi
#endif /* BTR_CUR_HASH_ADAPT */
	)
{
	fseg_inode_t*	inode;

	const uint32_t space_id = page_get_space_id(page_align(header));
	ut_ad(mtr->is_named_space(space_id));

	fil_space_t*		space = mtr->x_lock_space(space_id);
	buf_block_t*		iblock;

	inode = fseg_inode_try_get(header, space_id, space->zip_size(),
				   mtr, &iblock);
	if (space->is_stopping()) {
		return true;
	}

	if (!inode) {
		ib::warn() << "Double free of "
			   << page_id_t(space_id,
					page_get_page_no(page_align(header)));
		return true;
	}

	if (!space->full_crc32()) {
		fil_block_check_type(*iblock, FIL_PAGE_INODE, mtr);
	}

	dberr_t err;
	if (xdes_t* descr = fseg_get_first_extent(inode, space, mtr, &err)) {
		/* Free the extent held by the segment */
		return fseg_free_extent(inode, iblock, space,
					xdes_get_offset(descr),
					mtr
#ifdef BTR_CUR_HASH_ADAPT
					, ahi
#endif /* BTR_CUR_HASH_ADAPT */
					) != DB_SUCCESS;
	} else if (err != DB_SUCCESS) {
		return true;
	}

	/* Free a frag page */

	ulint n = fseg_find_last_used_frag_page_slot(inode);

	if (UNIV_UNLIKELY(n == ULINT_UNDEFINED)) {
		return true;
	}

	uint32_t page_no = fseg_get_nth_frag_page_no(inode, n);

	if (page_no == page_get_page_no(page_align(header))) {
		return true;
	}

	if (fseg_free_page_low(inode, iblock, space, page_no, mtr
#ifdef BTR_CUR_HASH_ADAPT
			       , ahi
#endif /* BTR_CUR_HASH_ADAPT */
			       ) != DB_SUCCESS) {
		return true;
	}
	buf_page_free(space, page_no, mtr);
	return false;
}

/** Returns the first extent descriptor for a segment.
We think of the extent lists of the segment catenated in the order
FSEG_FULL -> FSEG_NOT_FULL -> FSEG_FREE.
@param[in]	inode		segment inode
@param[in]	space		tablespace
@param[in,out]	mtr		mini-transaction
@return the first extent descriptor
@retval nullptr if none, or on corruption */
MY_ATTRIBUTE((nonnull, warn_unused_result))
static
xdes_t*
fseg_get_first_extent(
	fseg_inode_t*		inode,
	const fil_space_t*	space,
	mtr_t*			mtr,
	dberr_t*		err)
{
  if (UNIV_UNLIKELY(space->id != page_get_space_id(page_align(inode)) ||
                    memcmp(inode + FSEG_MAGIC_N, FSEG_MAGIC_N_BYTES, 4)))
  {
  corrupted:
    *err= DB_CORRUPTION;
    return nullptr;
  }

  fil_addr_t first;

  if (flst_get_len(inode + FSEG_FULL))
    first= flst_get_first(inode + FSEG_FULL);
  else if (flst_get_len(inode + FSEG_NOT_FULL))
    first= flst_get_first(inode + FSEG_NOT_FULL);
  else if (flst_get_len(inode + FSEG_FREE))
    first= flst_get_first(inode + FSEG_FREE);
  else
  {
    *err= DB_SUCCESS;
    return nullptr;
  }

  if (first.page == FIL_NULL)
    goto corrupted;

  return xdes_lst_get_descriptor(*space, first, mtr, nullptr, err);
}

#ifdef UNIV_BTR_PRINT
/*******************************************************************//**
Writes info of a segment. */
static void fseg_print_low(const fseg_inode_t *inode)
{
	ulint	space;
	ulint	n_used;
	ulint	n_frag;
	ulint	n_free;
	ulint	n_not_full;
	ulint	n_full;
	ulint	reserved;
	ulint	used;
	ulint	page_no;
	ib_id_t	seg_id;

	space = page_get_space_id(page_align(inode));
	page_no = page_get_page_no(page_align(inode));

	reserved = fseg_n_reserved_pages_low(inode, &used);

	seg_id = mach_read_from_8(inode + FSEG_ID);
	n_used = mach_read_from_4(inode + FSEG_NOT_FULL_N_USED);
	n_frag = fseg_get_n_frag_pages(inode);
	n_free = flst_get_len(inode + FSEG_FREE);
	n_not_full = flst_get_len(inode + FSEG_NOT_FULL);
	n_full = flst_get_len(inode + FSEG_FULL);

	ib::info() << "SEGMENT id " << seg_id
		<< " space " << space << ";"
		<< " page " << page_no << ";"
		<< " res " << reserved << " used " << used << ";"
		<< " full ext " << n_full << ";"
		<< " fragm pages " << n_frag << ";"
		<< " free extents " << n_free << ";"
		<< " not full extents " << n_not_full << ": pages " << n_used;

	ut_ad(!memcmp(FSEG_MAGIC_N_BYTES, FSEG_MAGIC_N + inode, 4));
}

/*******************************************************************//**
Writes info of a segment. */
void
fseg_print(
/*=======*/
	fseg_header_t*	header, /*!< in: segment header */
	mtr_t*		mtr)	/*!< in/out: mini-transaction */
{
  const fil_space_t *space=
    mtr->x_lock_space(page_get_space_id(page_align(header)));
  buf_block_t *block;
  if (fseg_inode_t *inode=
      fseg_inode_try_get(header, space->id, space->zip_size(), mtr, &block))
    fseg_print_low(inode);
}
#endif /* UNIV_BTR_PRINT */

#ifdef UNIV_DEBUG
std::ostream &fseg_header::to_stream(std::ostream &out) const
{
  out << "[fseg_header_t: space="
      << mach_read_from_4(m_header + FSEG_HDR_SPACE)
      << ", page=" << mach_read_from_4(m_header + FSEG_HDR_PAGE_NO)
      << ", offset=" << mach_read_from_2(m_header + FSEG_HDR_OFFSET) << "]";
  return out;
}
#endif /* UNIV_DEBUG */

/** Get the latched extent descriptor page or
acquire the extent descriptor page.
@param page_id  page identifier to be acquired
@param mtr      mini-transaction
@param err      error code
@return block descriptor */
static
buf_block_t *fsp_get_latched_xdes_page(
  page_id_t page_id, mtr_t *mtr, dberr_t *err)
{
  buf_block_t *block= nullptr;
  block= mtr->get_already_latched(
    page_id, MTR_MEMO_PAGE_SX_FIX);
  if (block)
    return block;
  return buf_page_get_gen(
    page_id, 0, RW_SX_LATCH, nullptr,
    BUF_GET_POSSIBLY_FREED, mtr, err);
}

/** Used during system tablespace truncation. Stores
the "to be modified" extent descriptor page and its
old page state */
class fsp_xdes_old_page
{
  std::vector<buf_block_t*> m_old_xdes_pages;
  const uint32_t m_space;
public:
  fsp_xdes_old_page(uint32_t space):m_space(space) {}
  ulint n_pages()
  {
    uint32_t count=0;
    for (uint32_t i= 0; i < m_old_xdes_pages.size(); i++)
      if (m_old_xdes_pages[i]) count++;
    return count;
  }

  __attribute__((warn_unused_result))
  dberr_t insert(uint32_t page_no, mtr_t *mtr)
  {
    uint32_t m_index= page_no >> srv_page_size_shift;
    if (m_old_xdes_pages.size() > m_index &&
        m_old_xdes_pages[m_index] != nullptr)
      return DB_SUCCESS;

    DBUG_EXECUTE_IF("shrink_buffer_pool_full",
                    return DB_OUT_OF_MEMORY;);
    dberr_t err= DB_SUCCESS;
    buf_block_t *block= fsp_get_latched_xdes_page(
                          page_id_t(m_space, page_no), mtr, &err);
    if (block)
    {
      buf_block_t *old= buf_LRU_get_free_block(have_no_mutex_soft);
      if (!old) return DB_OUT_OF_MEMORY;

      memcpy_aligned<UNIV_PAGE_SIZE_MIN>(
        old->page.frame, block->page.frame, srv_page_size);

      if (m_index >= m_old_xdes_pages.size())
        m_old_xdes_pages.resize(m_index + 1);
      m_old_xdes_pages[m_index] = old;
    }
    return err;
  }

  buf_block_t *search(uint32_t page_no)
  {
    uint32_t m_index= page_no >> srv_page_size_shift;
    if (m_index > m_old_xdes_pages.size())
      return nullptr;
    return m_old_xdes_pages[m_index];
  }

  void restore(mtr_t *mtr)
  {
    for (uint32_t i= 0; i < m_old_xdes_pages.size(); i++)
    {
      if (m_old_xdes_pages[i] == nullptr) continue;
      buf_block_t *block= mtr->get_already_latched(
        page_id_t{m_space, i << srv_page_size_shift},
        MTR_MEMO_PAGE_SX_FIX);
      ut_ad(block);
      memcpy_aligned<UNIV_PAGE_SIZE_MIN>(
        block->page.frame, m_old_xdes_pages[i]->page.frame, srv_page_size);
    }
  }

  ~fsp_xdes_old_page()
  {
    for (uint32_t i= 0; i < m_old_xdes_pages.size(); i++)
      if (m_old_xdes_pages[i])
        buf_block_free(m_old_xdes_pages[i]);
  }
};

/** Update the current descriptor entry with last valid
descriptor entry with skipped descriptor pages
@param header          File segment header
@param hdr_offset      FSP_FREE or FSP_FREE_FRAG
@param cur_addr        current descriptor
@param last_valid_addr last valid descriptor
@param skip_len        number of truncated extent descriptor entry
@param mtr             mini-transaction
@return error code or DB_SUCCESS */
__attribute__((warn_unused_result))
static
dberr_t fsp_lst_update_skip(
  buf_block_t *header, uint16_t hdr_offset,
  fil_addr_t cur_addr, fil_addr_t last_valid_addr,
  uint32_t skip_len, mtr_t *mtr)
{
  dberr_t err= DB_SUCCESS;
  uint32_t space_id= header->page.id().space();
  buf_block_t *cur= fsp_get_latched_xdes_page(
    page_id_t(space_id, cur_addr.page), mtr, &err);

  if (!cur) return err;
  if (last_valid_addr.page == FIL_NULL)
  {
    /* First node, so update the FIRST pointer of base
    with current extent descriptor and update
    the PREV pointer of last valid descriptor with
    FIL_NULL */
    flst_write_addr(
      *header,
      header->page.frame + hdr_offset + FLST_FIRST,
      cur_addr.page, cur_addr.boffset, mtr);

    flst_write_addr(
      *cur,
      cur->page.frame + cur_addr.boffset + FLST_PREV,
      last_valid_addr.page, last_valid_addr.boffset, mtr);
  }
  else
  {
    buf_block_t *prev= nullptr;
    if (cur->page.id().page_no() == last_valid_addr.page)
      prev= cur;
    else
    {
      prev= fsp_get_latched_xdes_page(
              page_id_t(space_id, last_valid_addr.page),
              mtr, &err);
      if (!prev) return err;
    }

    /* Update the NEXT pointer of last valid extent
    descriptor entry with current extent descriptor */
    flst_write_addr(
      *prev,
      prev->page.frame + last_valid_addr.boffset + FLST_NEXT,
      cur_addr.page, cur_addr.boffset, mtr);

    /* Update the PREV pointer of current extent
    descriptor entry with last valid extent descriptor */
    flst_write_addr(
      *cur,
      cur->page.frame + cur_addr.boffset + FLST_PREV,
      last_valid_addr.page, last_valid_addr.boffset, mtr);
  }

  byte *len_bytes= &header->page.frame[hdr_offset + FLST_LEN];
  uint32_t len= mach_read_from_4(len_bytes);
  ut_ad(len > skip_len);
  mtr->write<4>(*header, len_bytes, len - skip_len);
  return DB_SUCCESS;
}

/** Write the FLST_NEXT pointer of the last valid node with FIL_NULL
@param header          File segment header
@param hdr_offset      FSP_HEADER_OFFSET + FSP_FREE or FSP_FREE_FRAG
@param cur_addr        current descriptor
@param skip_len        number of truncated extent descriptor entry
@param orig_len        original length of the list
@param mtr             mini-transaction
@return error code or DB_SUCCESS */
__attribute__((warn_unused_result))
dberr_t
fsp_lst_write_end(
  buf_block_t *header, uint16_t hdr_offset,
  fil_addr_t cur_addr, uint32_t skip_len, uint32_t orig_len,
  mtr_t *mtr)
{
  dberr_t err= DB_SUCCESS;
  byte *len_bytes= &header->page.frame[hdr_offset + FLST_LEN];
  uint32_t len= mach_read_from_4(len_bytes);
  if (skip_len == 0)
  {
func_exit:
    if (hdr_offset == FSP_FREE_FRAG + FSP_HEADER_OFFSET)
    {
      byte *frag_used_byte= &header->page.frame[
        FSP_HEADER_OFFSET + FSP_FRAG_N_USED];
      uint32_t n_used_frag= mach_read_from_4(frag_used_byte);
      /* Update the FSP_FRAG_N_USED value after removing
      the truncated pages from FSP_FREE_FRAG list */
      if (len != orig_len)
        mtr->write<4>(*header, frag_used_byte,
                      n_used_frag - ((orig_len - len) * 2));
    }
    return DB_SUCCESS;
  }

  if (cur_addr.page == FIL_NULL)
  {
    /* There is no list, so reset base node */
    mtr->memset(
      header,
      FLST_FIRST + FIL_ADDR_PAGE + hdr_offset, 4, 0xff);
    mtr->memset(
      header,
      FLST_LAST + FIL_ADDR_PAGE + hdr_offset, 4, 0xff);
  }
  else
  {
    /* Update the FLST_LAST pointer in base node with current
    valid extent descriptor and mark the FIL_NULL as next in
    current extent descriptr */
    flst_write_addr(
      *header,
      header->page.frame + hdr_offset + FLST_LAST,
      cur_addr.page, cur_addr.boffset, mtr);

    buf_block_t *cur_block= fsp_get_latched_xdes_page(
      page_id_t(header->page.id().space(), cur_addr.page),
      mtr, &err);

    if (!cur_block) return err;

    flst_write_addr(
      *cur_block,
      cur_block->page.frame + cur_addr.boffset + FLST_NEXT,
      FIL_NULL, 0, mtr);
  }

  ut_ad(len >= skip_len);
  len-= skip_len;
  mtr->write<4>(*header, len_bytes, len);
  goto func_exit;
}

/** Remove the truncated extents from the FSP_FREE list
@param header     tablespace header
@param hdr_offset FSP_FREE or FSP_FREE_FRAG
@param threshold  Remove the pages from the list which is
                  greater than threshold
@param mtr        mini-transaction to remove the extents
@return DB_SUCCESS on success or error code */
__attribute__((warn_unused_result))
static
dberr_t fsp_shrink_list(buf_block_t *header, uint16_t hdr_offset,
                        uint32_t threshold, mtr_t *mtr)
{
  ut_ad(mach_read_from_4(header->page.frame + FIL_PAGE_OFFSET) == 0);
  const uint32_t len= flst_get_len(hdr_offset + header->page.frame);
  if (len == 0)
    return DB_SUCCESS;

  buf_block_t *descr_block= nullptr;
  dberr_t err= DB_SUCCESS;
  uint32_t skip_len= 0;
  fil_addr_t last_valid_addr {FIL_NULL, 0}, next_addr{FIL_NULL, 0};
  fil_addr_t addr= flst_get_first(header->page.frame + hdr_offset);

  for (uint32_t i= len; i > 0; i--)
  {
    ut_d(fil_space_t *space= header->page.id().space() == 0
                             ? fil_system.sys_space
                             : fil_system.temp_space);
    ut_ad(addr.page < space->size);
    ut_ad(!(addr.page & (srv_page_size - 1)));
    if (!descr_block || descr_block->page.id().page_no() != addr.page)
    {
      descr_block= fsp_get_latched_xdes_page(
        page_id_t(header->page.id().space(), addr.page), mtr, &err);
      if (!descr_block)
        return err;
    }

    if (addr.page < threshold)
    {
      /* Update only if only non-truncated page */
      if (skip_len)
      {
        err= fsp_lst_update_skip(
          header, hdr_offset, addr, last_valid_addr, skip_len, mtr);
        if (err) return err;
        skip_len= 0;
      }

      if (threshold <= xdes_get_offset(
            descr_block->page.frame + addr.boffset - XDES_FLST_NODE))
        skip_len++;
      else last_valid_addr= addr;
    }
    else skip_len++;

    next_addr= flst_get_next_addr(
      descr_block->page.frame + addr.boffset);
    if (next_addr.page != addr.page && addr.page >= threshold)
    {
      mtr->release_last_page();
      descr_block= nullptr;
    }

    if (next_addr.page == FIL_NULL)
    {
      err= fsp_lst_write_end(header, hdr_offset, last_valid_addr,
                             skip_len, len, mtr);
      break;
    }
    addr= next_addr;
  }
  ut_d(if (err == DB_SUCCESS) flst_validate(header, hdr_offset, mtr););
  return err;
}

/** Reset the XDES_BITMAP for the truncated extents
@param  space      tablespace to be truncated
@param  threshold  truncated size
@param  mtr        mini-transaction to reset XDES_BITMAP
@return DB_SUCCESS or error code on failure */
__attribute__((warn_unused_result))
static
dberr_t fsp_xdes_reset(uint32_t space_id, uint32_t threshold, mtr_t *mtr)
{
  if (!(threshold & (srv_page_size - 1)))
    return DB_SUCCESS;

  uint32_t cur_descr_page= xdes_calc_descriptor_page(0, threshold);
  ulint descr_offset= XDES_ARR_OFFSET + XDES_SIZE
          * xdes_calc_descriptor_index(0, threshold);
  ulint last_descr_offset= XDES_ARR_OFFSET + XDES_SIZE
          * xdes_calc_descriptor_index(
               0, (cur_descr_page + srv_page_size - 1));
  last_descr_offset+= XDES_SIZE;
  dberr_t err= DB_SUCCESS;
  buf_block_t *block= fsp_get_latched_xdes_page(
    page_id_t(space_id, cur_descr_page), mtr, &err);
  if (!block)
    return err;
  mtr->memset(
    block, descr_offset, (last_descr_offset - descr_offset), 0);
  return err;
}

/** This function does 2 things by traversing all the used
extents in the system tablespace
1) Find the last used extent
2) Store the old page frame of the "to be modified" extent
descriptor pages.
@param space             system tablespace
@param last_used_extent  value is 0 in case of finding the last used
                         extent; else it could be last used extent
@param old_xdes_entry    nullptr or object to store the
                         old page content of "to be modified"
                         extent descriptor pages
@return DB_SUCCESS or error code */
__attribute__((warn_unused_result))
dberr_t fsp_traverse_extents(
  fil_space_t *space, uint32_t *last_used_extent, mtr_t *mtr,
  fsp_xdes_old_page *old_xdes_entry= nullptr)
{
  dberr_t err= DB_SUCCESS;
  bool find_last_used_extent= (old_xdes_entry == nullptr);
  uint32_t threshold= *last_used_extent;
  uint32_t last_descr_page_no= xdes_calc_descriptor_page(
    0, space->free_limit - 1);

  if (find_last_used_extent)
    *last_used_extent= space->free_limit;
  else
  {
    err= old_xdes_entry->insert(0, mtr);
    if (err) return err;
    if (threshold & (srv_page_size - 1))
      err= old_xdes_entry->insert(
        xdes_calc_descriptor_page(0, threshold), mtr);
  }

  buf_block_t *block= nullptr;
  std::vector<uint32_t> modified_xdes;

  for (uint32_t cur_extent=
       ((space->free_limit - 1)/ FSP_EXTENT_SIZE) * FSP_EXTENT_SIZE;
       cur_extent >= threshold;)
  {
    if (!block)
    {
      block= fsp_get_latched_xdes_page(
               page_id_t(space->id, last_descr_page_no),
               mtr, &err);
      if (!block) return err;
    }

    xdes_t *descr= XDES_ARR_OFFSET + XDES_SIZE
      * xdes_calc_descriptor_index(0, cur_extent)
      + block->page.frame;

    if (find_last_used_extent)
    {
      ulint state= xdes_get_state(descr);
      if (state == XDES_FREE)
        *last_used_extent= cur_extent;
      else if (state == XDES_FREE_FRAG &&
               !(cur_extent & (srv_page_size - 1)) &&
               xdes_get_n_used(descr) == 2)
        /* Extent Descriptor Page */
        *last_used_extent= cur_extent;
      else return DB_SUCCESS;
    }
    else
    {
      fil_addr_t prev_addr= flst_get_prev_addr(
                              descr + XDES_FLST_NODE);
      ut_ad(prev_addr.page < space->size ||
            prev_addr.page == FIL_NULL);
      ut_ad(prev_addr.page == FIL_NULL ||
            !(prev_addr.page & (srv_page_size - 1)));

      fil_addr_t next_addr= flst_get_next_addr(
                              descr + XDES_FLST_NODE);
      ut_ad(next_addr.page < space->size ||
            next_addr.page == FIL_NULL);
      ut_ad(next_addr.page == FIL_NULL ||
            !(next_addr.page & (srv_page_size - 1)));

      if (prev_addr.page < threshold)
        modified_xdes.push_back(prev_addr.page);

      if (next_addr.page < threshold)
        modified_xdes.push_back(next_addr.page);
    }

    cur_extent-= FSP_EXTENT_SIZE;
    uint32_t cur_descr_page= xdes_calc_descriptor_page(0, cur_extent);
    if (last_descr_page_no != cur_descr_page)
    {
      if (last_descr_page_no >= threshold)
        mtr->release_last_page();
      last_descr_page_no= cur_descr_page;
      block= nullptr;
    }
  }

  if (!find_last_used_extent)
  {
    for (auto it : modified_xdes)
    {
      err= old_xdes_entry->insert(it, mtr);
      if (err) return err;
    }
    modified_xdes.clear();
  }
  return err;
}

#ifdef UNIV_DEBUG
/** Validate the system tablespace list */
__attribute__((warn_unused_result))
dberr_t fsp_tablespace_validate(fil_space_t *space)
{
  /* Validate all FSP list in system tablespace */
  mtr_t local_mtr;
  dberr_t err= DB_SUCCESS;
  local_mtr.start();
  if (buf_block_t *header= fsp_get_header(
        space, &local_mtr, &err))
  {
    flst_validate(header, FSP_FREE + FSP_HEADER_OFFSET, &local_mtr);
    flst_validate(header, FSP_FREE_FRAG + FSP_HEADER_OFFSET,
                  &local_mtr);
    flst_validate(header, FSP_HEADER_OFFSET + FSP_FULL_FRAG,
                  &local_mtr);
    flst_validate(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FULL,
                  &local_mtr);
    flst_validate(header, FSP_HEADER_OFFSET + FSP_SEG_INODES_FREE,
                  &local_mtr);
  }
  local_mtr.commit();
  return err;
}
#endif /* UNIV_DEBUG */

void fsp_system_tablespace_truncate()
{
  uint32_t last_used_extent= 0;
  fil_space_t *space= fil_system.sys_space;
  mtr_t mtr;
  mtr.start();
  mtr.x_lock_space(space);
  dberr_t err= fsp_traverse_extents(space, &last_used_extent, &mtr);
  if (err != DB_SUCCESS)
  {
func_exit:
    sql_print_warning("InnoDB: Cannot shrink the system tablespace "
                      "due to %s", ut_strerr(err));
    mtr.commit();
    return;
  }
  uint32_t fixed_size= srv_sys_space.get_min_size(),
           header_size= space->size_in_header;
  mtr.commit();

  if (last_used_extent >= header_size || fixed_size >= header_size)
    /* Tablespace is being used within fixed size */
    return;

  /* Set fixed size as threshold to truncate */
  if (fixed_size > last_used_extent)
    last_used_extent= fixed_size;

  my_bool old_dblwr_buf= srv_use_doublewrite_buf;
  /* Flush all pages in buffer pool, so that it doesn't have to
  use doublewrite buffer and disable dblwr and there should
  be enough space in redo log */
  log_make_checkpoint();
  srv_use_doublewrite_buf= false;

  buf_block_t *header= nullptr;
  ut_ad(!fsp_tablespace_validate(space));

  mtr.start();
  mtr.x_lock_space(space);

  {
    /* Take the rough estimation of modified extent
    descriptor page and store their old state */
    fsp_xdes_old_page old_xdes_list(space->id);
    err= fsp_traverse_extents(space, &last_used_extent, &mtr, &old_xdes_list);

    if (err == DB_OUT_OF_MEMORY)
    {
      mtr.commit();
      sql_print_warning("InnoDB: Cannot shrink the system "
                        "tablespace from " UINT32PF" to "
                        UINT32PF " pages due to insufficient "
                        "innodb_buffer_pool_size", space->size,
                        last_used_extent);
      return;
    }

    sql_print_information("InnoDB: Truncating system tablespace from "
                          UINT32PF " to " UINT32PF " pages", space->size,
                          last_used_extent);

    header= fsp_get_latched_xdes_page(
              page_id_t(space->id, 0), &mtr, &err);
    if (!header)
      goto func_exit;

    mtr.write<4, mtr_t::FORCED>(
      *header, FSP_HEADER_OFFSET + FSP_SIZE + header->page.frame,
      last_used_extent);

    if (space->free_limit > last_used_extent)
      mtr.write<4,mtr_t::MAYBE_NOP>(*header, FSP_HEADER_OFFSET
                                    + FSP_FREE_LIMIT + header->page.frame,
                                    last_used_extent);
    err= fsp_shrink_list(
      header, FSP_HEADER_OFFSET + FSP_FREE, last_used_extent, &mtr);
    if (err != DB_SUCCESS)
      goto func_exit;

    err= fsp_shrink_list(
      header, FSP_HEADER_OFFSET + FSP_FREE_FRAG, last_used_extent, &mtr);
    if (err != DB_SUCCESS)
      goto func_exit;

    err= fsp_xdes_reset(space->id, last_used_extent, &mtr);
    if (err != DB_SUCCESS)
      goto func_exit;

    mtr.trim_pages(page_id_t(0, last_used_extent));
    size_t shrink_redo_size= mtr.get_log_size();

    DBUG_EXECUTE_IF("mtr_log_max_size", goto mtr_max;);
    if (shrink_redo_size >
          (2 << 20) - 8 /* encryption nonce */ - 5 /* EOF, checksum */)
    {
#ifndef DBUG_OFF
mtr_max:
#endif
      /* Replace the modified copy from buffer pool with
      original copy of the pages. */
      old_xdes_list.restore(&mtr);
      mtr.discard_modifications();
      mtr.commit();
      ut_ad(!fsp_tablespace_validate(space));
      sql_print_error(
        "InnoDB: Cannot shrink the system tablespace "
        "because the mini-transaction log size (%zu bytes) "
        "exceeds 2 MiB", shrink_redo_size + 8 + 5);
      return;
    }
  }

  if (space->free_limit > last_used_extent)
    space->free_limit= last_used_extent;
  space->free_len= flst_get_len(FSP_HEADER_OFFSET + FSP_FREE +
                                header->page.frame);

  mtr.commit_shrink(*space, last_used_extent);
  sql_print_information("InnoDB: System tablespace truncated successfully");
  srv_use_doublewrite_buf= old_dblwr_buf;
}

inline void fil_space_t::clear_freed_ranges(uint32_t threshold)
{
  ut_ad(id == SRV_TMP_SPACE_ID);
  std::lock_guard<std::mutex> freed_lock(freed_range_mutex);
  range_set current_ranges;
  for (const auto &range : freed_ranges)
  {
    if (range.first >= threshold)
      continue;
    else if (range.last > threshold)
    {
      range_t new_range{range.first, threshold - 1};
      current_ranges.add_range(new_range);
      continue;
    }
    current_ranges.add_range(range);
  }
  freed_ranges= std::move(current_ranges);
}

void fsp_shrink_temp_space()
{
  uint32_t last_used_extent= 0;
  fil_space_t *space= fil_system.temp_space;
  mtr_t mtr;
  mtr.start();
  mtr.set_log_mode(MTR_LOG_NO_REDO);
  mtr.x_lock_space(space);
  dberr_t err= fsp_traverse_extents(space, &last_used_extent, &mtr);
  if (err != DB_SUCCESS)
  {
func_exit:
    sql_print_warning("InnoDB: Cannot shrink the temporary tablespace "
                      "due to %s", ut_strerr(err));
    mtr.commit();
    return;
  }
  uint32_t fixed_size= srv_tmp_space.get_min_size(),
           header_size= space->size_in_header;

  if (last_used_extent >= header_size || fixed_size >= header_size)
  {
    /* Tablespace is being used within fixed size */
    mtr.commit();
    return;
  }

  /* Set fixed size as threshold to truncate */
  if (fixed_size > last_used_extent)
    last_used_extent= fixed_size;

  sql_print_information("InnoDB: Truncating temporary tablespace from "
                        UINT32PF " to " UINT32PF " pages", space->size,
                        last_used_extent);

  buf_block_t *header= fsp_get_latched_xdes_page(
      page_id_t(space->id, 0), &mtr, &err);
  if (!header)
    goto func_exit;

  mach_write_to_4(
    FSP_HEADER_OFFSET + FSP_SIZE + header->page.frame,
    last_used_extent);

  if (space->free_limit > last_used_extent)
    mach_write_to_4(
      FSP_HEADER_OFFSET + FSP_FREE_LIMIT + header->page.frame,
      last_used_extent);

  mtr.set_modified(*header);

  err= fsp_shrink_list(header, FSP_HEADER_OFFSET + FSP_FREE,
                       last_used_extent, &mtr);

  if (err != DB_SUCCESS)
    goto func_exit;

  err= fsp_shrink_list(
         header, FSP_HEADER_OFFSET + FSP_FREE_FRAG,
         last_used_extent, &mtr);
  DBUG_EXECUTE_IF("fail_temp_truncate", err= DB_ERROR;);
  if (err != DB_SUCCESS)
    goto func_exit;

  err= fsp_xdes_reset(space->id, last_used_extent, &mtr);
  if (err != DB_SUCCESS)
    goto func_exit;

  space->clear_freed_ranges(last_used_extent);
  buf_LRU_truncate_temp(last_used_extent);
  mysql_mutex_lock(&fil_system.mutex);

  space->size= last_used_extent;
  if (space->free_limit > last_used_extent)
    space->free_limit= space->size;

  space->free_len= flst_get_len(
    FSP_HEADER_OFFSET + FSP_FREE+ header->page.frame);

  /* Last file new size after truncation */
  uint32_t new_last_file_size=
    last_used_extent -
    (fixed_size - srv_tmp_space.m_files.at(
     srv_tmp_space.m_files.size() - 1).param_size());

  space->size_in_header= space->size;
  space->chain.end->size= new_last_file_size;
  srv_tmp_space.set_last_file_size(new_last_file_size);
  mysql_mutex_unlock(&fil_system.mutex);
  os_file_truncate(
    space->chain.end->name, space->chain.end->handle,
    os_offset_t{space->chain.end->size} << srv_page_size_shift, true);
  mtr.commit();
  sql_print_information("InnoDB: Temporary tablespace truncated successfully");
}


static uint32_t binlog_size_in_pages;
buf_block_t *binlog_cur_block;
uint32_t binlog_cur_page_no;
uint32_t binlog_cur_page_offset;
/*
  Mutex protecting active_binlog_file_no and active_binlog_space.
*/
mysql_mutex_t active_binlog_mutex;
pthread_cond_t active_binlog_cond;
static std::thread binlog_prealloc_thr_obj;
static bool prealloc_thread_end= false;
/* The currently being written binlog tablespace. */
std::atomic<uint64_t> active_binlog_file_no;
fil_space_t* active_binlog_space;
/*
  The first binlog tablespace that is still open.
  This can be equal to active_binlog_file_no, if the tablespace prior to the
  active one has been fully flushed out to disk and closed.
  Or it can be one less, if the prior tablespace is still being written out and
  closed.
*/
std::atomic<uint64_t> first_open_binlog_file_no;
/*
  The most recent created and open tablespace.
  This can be equal to active_binlog_file_no+1, if the next tablespace to be
  used has already been pre-allocated and opened.
  Or it can be the same as active_binlog_file_no, if the pre-allocation of the
  next tablespace is still pending.
*/
uint64_t last_created_binlog_file_no;
fil_space_t *last_created_binlog_space;

/*
  Point at which it is guaranteed that all data has been written out to the
  binlog file (on the OS level; not necessarily fsync()'ed yet).

  Stores the most recent two values, each corresponding to active_binlog_file_no&1.
*/
/* ToDo: maintain this offset value as up to where data has been written out to the OS. Needs to be binary-searched in current binlog file at server restart; which is also a reason why it might not be a multiple of the page size. */
std::atomic<uint64_t> binlog_cur_written_offset[2];
/* Offset of last valid byte of data in most recent 2 binlog files. */
std::atomic<uint64_t> binlog_cur_end_offset[2];

static void fsp_binlog_prealloc_thread();
static int fsp_binlog_discover();


#define BINLOG_NAME_BASE "binlog-"
#define BINLOG_NAME_EXT ".ibb"
/* '.' + '/' + "binlog-" + (<=20 digits) + '.' + "ibb" + '\0'. */
#define BINLOG_NAME_LEN 1 + 1 + 7 + 20 + 1 + 3 + 1
static inline void
binlog_name_make(char name_buf[BINLOG_NAME_LEN], uint64_t file_no)
{
  sprintf(name_buf, "./" BINLOG_NAME_BASE "%06" PRIu64 BINLOG_NAME_EXT,
          file_no);
}


/*
  Check if this is an InnoDB binlog file name.
  Return the index/file_no if so.
*/
static bool
is_binlog_name(const char *name, uint64_t *out_idx)
{
  const size_t base_len= sizeof(BINLOG_NAME_BASE) - 1;  // Length without '\0' terminator
  const size_t ext_len= sizeof(BINLOG_NAME_EXT) - 1;

  if (0 != strncmp(name, BINLOG_NAME_BASE, base_len))
    return false;
  size_t name_len= strlen(name);
  if (name_len < base_len + 1 + ext_len)
    return false;
  const char *ext_start= name + (name_len - ext_len);
  if (0 != strcmp(ext_start, BINLOG_NAME_EXT))
    return false;
  if (!std::isdigit((unsigned char)(name[base_len])))
    return false;
  char *conv_end= nullptr;
  unsigned long long idx= std::strtoull(name + base_len, &conv_end, 10);
  if (idx == ULLONG_MAX || conv_end != ext_start)
    return false;

  *out_idx= (uint64_t)idx;
  return true;
}


/** Write out all pages, flush, and close/detach a binlog tablespace.
@param[in] file_no	 Index of the binlog tablespace
@return DB_SUCCESS or error code */
static dberr_t
fsp_binlog_tablespace_close(uint64_t file_no)
{
  dberr_t res;

  uint32_t space_id= SRV_SPACE_ID_BINLOG0 + (file_no & 1);
  mysql_mutex_lock(&fil_system.mutex);
  fil_space_t *space= fil_space_get_by_id(space_id);
  mysql_mutex_unlock(&fil_system.mutex);
  if (!space) {
    res= DB_ERROR;
    goto end;
  }

  /*
    Write out any remaining pages in the buffer pool to the binlog tablespace.
    Then flush the file to disk, and close the old tablespace.
  */
  while (buf_flush_list_space(space))
    ;
  os_aio_wait_until_no_pending_writes(false);
  space->flush<false>();
  mysql_mutex_lock(&fil_system.mutex);
  fil_system.detach(space, false);
  mysql_mutex_unlock(&fil_system.mutex);

  res= DB_SUCCESS;
end:
  return res;
}


/*
  Initialize the InnoDB implementation of binlog.
  Note that we do not create or open any binlog tablespaces here.
  This is only done if InnoDB binlog is enabled on the server level.
*/
void
fsp_binlog_init()
{
  mysql_mutex_init(fsp_active_binlog_mutex_key, &active_binlog_mutex, nullptr);
  pthread_cond_init(&active_binlog_cond, nullptr);
}


/*
  Open the InnoDB binlog implementation.
  This is called from server binlog layer if the user configured the binlog to
  use the innodb implementation (with --binlog-storage-engine=innodb).
*/
bool
innodb_binlog_init(size_t binlog_size)
{
  uint64_t pages= binlog_size >> srv_page_size_shift;
  if (UNIV_LIKELY(pages > (uint64_t)UINT32_MAX)) {
    pages= UINT32_MAX;
    ib::warn() << "Requested max_binlog_size is larger than the maximum " <<
      "InnoDB tablespace size, truncated to " <<
      (pages << srv_page_size_shift) << ".";
  } else if (pages < 2) {  /* Minimum one data page and one index page. */
    pages= 2;
    ib::warn() << "Requested max_binlog_size is smaller than the minimum " <<
      "size supported by InnoDB, truncated to " <<
      (pages << srv_page_size_shift) << ".";
  }
  binlog_size_in_pages= (uint32_t)pages;

  first_open_binlog_file_no.store(~(uint64_t)0, std::memory_order_relaxed);
  last_created_binlog_file_no= ~(uint64_t)0;
  active_binlog_file_no.store(~(uint64_t)0, std::memory_order_release);
  active_binlog_space= nullptr;
  binlog_cur_page_no= 0;
  binlog_cur_page_offset= FIL_PAGE_DATA;
  /* Find any existing binlog files and continue writing in them. */
  fsp_binlog_discover();

  /* Start pre-allocating new binlog files. */
  binlog_prealloc_thr_obj= std::thread{fsp_binlog_prealloc_thread};

  mysql_mutex_lock(&active_binlog_mutex);
  while (last_created_binlog_file_no == ~(uint64_t)0) {
    /* Wait for the first binlog file to be available. */
    my_cond_wait(&active_binlog_cond, &active_binlog_mutex.m_mutex);
  }
  mysql_mutex_unlock(&active_binlog_mutex);

  return false;
}


struct found_binlogs {
  uint64_t last_file_no, prev_file_no;
  size_t last_size, prev_size;
  int found_binlogs;
};


/* Compute the (so far) last and last-but-one binlog files found. */
static void
process_binlog_name(found_binlogs *bls, uint64_t idx, size_t size)
{
  if (bls->found_binlogs == 0 ||
      idx > bls->last_file_no) {
    if (bls->found_binlogs >= 1 && idx == bls->last_file_no + 1) {
      bls->prev_file_no= bls->last_file_no;
      bls->prev_size= bls->last_size;
      bls->found_binlogs= 2;
    } else {
      bls->found_binlogs= 1;
    }
    bls->last_file_no= idx;
    bls->last_size= size;
  } else if (bls->found_binlogs == 1 && idx + 1 == bls->last_file_no) {
    bls->found_binlogs= 2;
    bls->prev_file_no= idx;
    bls->prev_size= size;
  }
}


/*
  Open an existing tablespace. The filehandle fh is taken over by the tablespace
  (or closed in case of error).
*/
static fil_space_t *
fsp_binlog_open(const char *file_name, pfs_os_file_t fh,
                uint64_t file_no, size_t file_size, bool open_empty)
{
  const uint32_t page_size= (uint32_t)srv_page_size;
  const uint32_t page_size_shift= srv_page_size_shift;

  os_offset_t binlog_size= max_binlog_size;
  if (open_empty && file_size < binlog_size) {
    /*
      A crash may have left a partially pre-allocated file. If so, extend it
      to the required size.
      Note that this may also extend a previously pre-allocated file to the new
      binlog configured size, if the configuration changed during server
      restart.
    */
    if (!os_file_set_size(file_name, fh, binlog_size, false)) {
      ib::warn() << "Failed to change the size of InnoDB binlog file " <<
        file_name << " from " << file_size << " to " << binlog_size <<
        " bytes (error code: " << errno << ").";
    } else {
      file_size= binlog_size;
    }
  }
  if (file_size < 2*page_size)
  {
    ib::warn() << "InnoDB binlog file number " << file_no << " is too short"
      " (" << file_size << " bytes), should be at least " << 2*page_size <<
      " bytes.";
    os_file_close(fh);
    return nullptr;
  }

  uint32_t space_id= SRV_SPACE_ID_BINLOG0 + (file_no & 1);

  if (!open_empty) {
    page_t *page_buf= static_cast<byte*>(aligned_malloc(page_size, page_size));
    if (!page_buf) {
      os_file_close(fh);
      return nullptr;
    }

    dberr_t err= os_file_read(IORequestRead, fh, page_buf, 0, page_size, nullptr);
    if (err != DB_SUCCESS) {
      ib::warn() << "Unable to read first page of file " << file_name;
      aligned_free(page_buf);
      os_file_close(fh);
      return nullptr;
    }

    /* ToDo: Maybe use leaner page format for binlog tablespace? */
    uint32_t id1= mach_read_from_4(FIL_PAGE_SPACE_ID + page_buf);
    if (id1 != space_id) {
      ib::warn() << "Binlog file " << file_name <<
        " has inconsistent tablespace id " << id1 <<
        " (expected " << space_id << ")";
      aligned_free(page_buf);
      os_file_close(fh);
      return nullptr;
    }
    // ToDo: should we here check buf_page_is_corrupted() ?

    aligned_free(page_buf);
  }

  uint32_t fsp_flags=
    FSP_FLAGS_FCRC32_MASK_MARKER | FSP_FLAGS_FCRC32_PAGE_SSIZE();
  /* ToDo: Enryption. */
  fil_encryption_t mode= FIL_ENCRYPTION_OFF;
  fil_space_crypt_t* crypt_data= nullptr;
  fil_space_t *space;

  mysql_mutex_lock(&fil_system.mutex);
  if (!(space= fil_space_t::create(space_id, fsp_flags,
                                   FIL_TYPE_TABLESPACE, crypt_data,
                                   mode, true))) {
    mysql_mutex_unlock(&fil_system.mutex);
    os_file_close(fh);
    return nullptr;
  }

  space->add(file_name, fh, (uint32_t)(file_size >> page_size_shift),
             false, true);

  first_open_binlog_file_no.store(file_no, std::memory_order_release);
  if (last_created_binlog_file_no == ~(uint64_t)0 ||
      file_no > last_created_binlog_file_no) {
    last_created_binlog_file_no= file_no;
    last_created_binlog_space= space;
  }

  mysql_mutex_unlock(&fil_system.mutex);
  return space;
}


static bool
binlog_page_empty(const byte *page)
{
  return page[FIL_PAGE_DATA] == 0;
}


/*
  Find the last written position in the binlog file.
  Do a binary search through the pages to find the last non-empty page, then
  scan the page to find the place to start writing new binlog data.

  Returns:
     1 position found, output in *out_space, *out_page_no and *out_pos_in_page.
     0 binlog file is empty.
    -1 error.
*/

static int
find_pos_in_binlog(uint64_t file_no, size_t file_size, byte *page_buf,
                   fil_space_t **out_space,
                   uint32_t *out_page_no, uint32_t *out_pos_in_page)
{
  const uint32_t page_size= (uint32_t)srv_page_size;
  const uint32_t page_size_shift= (uint32_t)srv_page_size_shift;
  const uint32_t idx= file_no & 1;
  char file_name[BINLOG_NAME_LEN];
  uint32_t p_0, p_1, p_2, last_nonempty;
  dberr_t err;
  byte *p, *page_end;
  bool ret;

  *out_page_no= 0;
  *out_pos_in_page= FIL_PAGE_DATA;

  binlog_name_make(file_name, file_no);
  pfs_os_file_t fh= os_file_create(innodb_data_file_key, file_name,
                                   OS_FILE_OPEN | OS_FILE_ON_ERROR_NO_EXIT,
                                   OS_FILE_AIO, OS_DATA_FILE,
                                   srv_read_only_mode, &ret);
  if (!ret) {
    ib::warn() << "Unable to open file " << file_name;
    return -1;
  }

  err= os_file_read(IORequestRead, fh, page_buf, 0, page_size, nullptr);
  if (err != DB_SUCCESS) {
    os_file_close(fh);
    return -1;
  }
  if (binlog_page_empty(page_buf)) {
    *out_space= fsp_binlog_open(file_name, fh, file_no, file_size, true);
    binlog_cur_written_offset[idx].store(0, std::memory_order_relaxed);
    binlog_cur_end_offset[idx].store(0, std::memory_order_relaxed);
    return (*out_space ? 0 : -1);
  }
  last_nonempty= 0;

  /*
    During the binary search, p_0-1 is the largest page number that is know to
    be non-empty. And p_2 is the first page that is known to be empty.
  */
  p_0= 1;
  p_2= (uint32_t)(file_size / page_size);
  for (;;) {
    if (p_0 == p_2)
      break;
    ut_ad(p_0 < p_2);
    p_1= (p_0 + p_2) / 2;
    err= os_file_read(IORequestRead, fh, page_buf, p_1 << page_size_shift,
                      page_size, nullptr);
    if (err != DB_SUCCESS) {
      os_file_close(fh);
      return -1;
    }
    if (binlog_page_empty(page_buf)) {
      p_2= p_1;
    } else {
      p_0= p_1 + 1;
      last_nonempty= p_1;
    }
  }
  /* At this point, p_0 == p_2 is the first empty page. */
  ut_ad(p_0 >= 1);

  /*
    This sometimes does an extra read, but as this is only during startup it
    does not matter.
  */
  err= os_file_read(IORequestRead, fh, page_buf,
                    last_nonempty << page_size_shift, page_size, nullptr);
  if (err != DB_SUCCESS) {
    os_file_close(fh);
    return -1;
  }

  /* Now scan the last page to find the position in it to continue. */
  p= &page_buf[FIL_PAGE_DATA];
  page_end= &page_buf[page_size - FIL_PAGE_DATA_END];
  while (*p && p < page_end) {
    if (*p == 0xff) {
      p= page_end;
      break;
    }
    p += 3 + (((uint32_t)p[2] << 8) | ((uint32_t)p[1] & 0xff));
    // ToDo: How to handle page corruption?
    ut_a(p <= page_end);
  }

  *out_page_no= p_0 - 1;
  *out_pos_in_page= (uint32_t)(p - page_buf);

  *out_space= fsp_binlog_open(file_name, fh, file_no, file_size, false);
  uint64_t pos= (*out_page_no << page_size_shift) | *out_pos_in_page;
  binlog_cur_written_offset[idx].store(pos, std::memory_order_relaxed);
  binlog_cur_end_offset[idx].store(pos, std::memory_order_relaxed);
  return (*out_space ? 1 : -1);
}


/*
  Returns:
    -1     error
     0     No binlogs found
     1     Just one binlog file found
     2     Found two (or more) existing binlog files
*/
static int
fsp_binlog_discover()
{
  uint64_t file_no;
  const uint32_t page_size= (uint32_t)srv_page_size;
  const uint32_t page_size_shift= (uint32_t)srv_page_size_shift;
  MY_DIR *dir= my_dir(".", MYF(MY_WME|MY_WANT_STAT));  // ToDo: configurable binlog directory, and don't ask my_dir to stat every file found
  if (!dir)
    return -1;

  struct found_binlogs binlog_files;
  binlog_files.found_binlogs= 0;
  size_t num_entries= dir->number_of_files;
  fileinfo *entries= dir-> dir_entry;
  for (size_t i= 0; i < num_entries; ++i) {
    const char *name= entries[i].name;
    uint64_t idx;
    if (!is_binlog_name(name, &idx))
      continue;
    process_binlog_name(&binlog_files, idx, entries[i].mystat->st_size);
  }
  my_dirend(dir);

  /*
    Now, if we found any binlog files, locate the point in one of them where
    binlogging stopped, and where we should continue writing new binlog data.
  */
  fil_space_t *space, *prev_space;
  uint32_t page_no, prev_page_no, pos_in_page, prev_pos_in_page;
  // ToDo: Do we need aligned_malloc() for page_buf, to be able to read a page into it (like IO_DIRECT maybe) ?
  std::unique_ptr<byte[]> page_buf(new byte[page_size]);
  if (!page_buf)
    return -1;
  if (binlog_files.found_binlogs >= 1) {
    int res= find_pos_in_binlog(binlog_files.last_file_no,
                                binlog_files.last_size,
                                page_buf.get(),
                                &space, &page_no, &pos_in_page);
    if (res < 0) {
      file_no= binlog_files.last_file_no;
      active_binlog_file_no.store(file_no, std::memory_order_release);
      ib::warn() << "Binlog number " << binlog_files.last_file_no <<
        " could no be opened. Starting a new binlog file from number " <<
        (file_no + 1) << ".";
      return 0;
    }

    if (res > 0) {
      /* Found start position in the last binlog file. */
      file_no= binlog_files.last_file_no;
      active_binlog_file_no.store(file_no, std::memory_order_release);
      active_binlog_space= space;
      binlog_cur_page_no= page_no;
      binlog_cur_page_offset= pos_in_page;
      ib::info() << "Continuing binlog number " << file_no << " from position "
                 << (((uint64_t)page_no << page_size_shift) | pos_in_page)
                 << ".";
      return binlog_files.found_binlogs;
    }

    /* res == 0, the last binlog is empty. */
    if (binlog_files.found_binlogs >= 2) {
      /* The last binlog is empty, try the previous one. */
      res= find_pos_in_binlog(binlog_files.prev_file_no,
                              binlog_files.prev_size,
                              page_buf.get(),
                              &prev_space, &prev_page_no, &prev_pos_in_page);
      if (res < 0) {
        file_no= binlog_files.last_file_no;
        active_binlog_file_no.store(file_no, std::memory_order_release);
        active_binlog_space= space;
        binlog_cur_page_no= page_no;
        binlog_cur_page_offset= pos_in_page;
        ib::warn() << "Binlog number " << binlog_files.prev_file_no
                   << " could not be opened, starting from binlog number "
                   << file_no << " instead." ;
        return 1;
      }
      file_no= binlog_files.prev_file_no;
      active_binlog_file_no.store(file_no, std::memory_order_release);
      active_binlog_space= prev_space;
      binlog_cur_page_no= prev_page_no;
      binlog_cur_page_offset= prev_pos_in_page;
      ib::info() << "Continuing binlog number " << file_no << " from position "
                 << (((uint64_t)prev_page_no << page_size_shift) |
                     prev_pos_in_page)
                 << ".";
      return binlog_files.found_binlogs;
    }

    /* Just one empty binlog file found. */
    file_no= binlog_files.last_file_no;
    active_binlog_file_no.store(file_no, std::memory_order_release);
    active_binlog_space= space;
    binlog_cur_page_no= page_no;
    binlog_cur_page_offset= pos_in_page;
    ib::info() << "Continuing binlog number " << file_no << " from position "
               << FIL_PAGE_DATA << ".";
    return binlog_files.found_binlogs;
  }

  /* No binlog files found, start from scratch. */
  file_no= 0;
  ib::info() << "Starting a new binlog from file number " << file_no << ".";
  return 0;
}


void fsp_binlog_close()
{
  if (binlog_prealloc_thr_obj.joinable()) {
    mysql_mutex_lock(&active_binlog_mutex);
    prealloc_thread_end= true;
    pthread_cond_signal(&active_binlog_cond);
    mysql_mutex_unlock(&active_binlog_mutex);
    binlog_prealloc_thr_obj.join();
  }

  uint64_t file_no= first_open_binlog_file_no.load(std::memory_order_relaxed);
  if (file_no != ~(uint64_t)0) {
    if (file_no <= last_created_binlog_file_no) {
      fsp_binlog_tablespace_close(file_no);
      if (file_no + 1 <= last_created_binlog_file_no) {
        fsp_binlog_tablespace_close(file_no + 1);
      }
    }
  }
  /*
    ToDo: This doesn't seem to free all memory. I'm still getting leaks in eg. --valgrind. Find out why and fix. Example:
==3464576==    at 0x48407B4: malloc (vg_replace_malloc.c:381)
==3464576==    by 0x15318CD: mem_strdup(char const*) (mem0mem.inl:452)
==3464576==    by 0x15321DF: fil_space_t::add(char const*, pfs_os_file_t, unsigned int, bool, bool, unsigned int) (fil0fil.cc:306)
==3464576==    by 0x1558445: fsp_binlog_tablespace_create(unsigned long) (fsp0fsp.cc:3900)
==3464576==    by 0x1558C70: fsp_binlog_write_cache(st_io_cache*, unsigned long, mtr_t*) (fsp0fsp.cc:4013)
  */
  pthread_cond_destroy(&active_binlog_cond);
  mysql_mutex_destroy(&active_binlog_mutex);
}


/** Create a binlog tablespace file
@param[in]  file_no	 Index of the binlog tablespace
@param[out] new_space	 The newly created tablespace
@return DB_SUCCESS or error code */
dberr_t fsp_binlog_tablespace_create(uint64_t file_no, fil_space_t **new_space)
{
	pfs_os_file_t	fh;
	bool		ret;

        *new_space= nullptr;
	uint32_t size= binlog_size_in_pages;
	if(srv_read_only_mode)
		return DB_ERROR;

        char name[BINLOG_NAME_LEN];
        binlog_name_make(name, file_no);

	os_file_create_subdirs_if_needed(name);

	/* ToDo: Do we need here an mtr.log_file_op(FILE_CREATE) like in fil_ibd_create(()? */
	fh = os_file_create(
		innodb_data_file_key,
		name,
		OS_FILE_CREATE | OS_FILE_ON_ERROR_NO_EXIT,
		OS_FILE_AIO, OS_DATA_FILE, srv_read_only_mode, &ret);

	if (!ret) {
		os_file_close(fh);
		return DB_ERROR;
	}

	/* ToDo: Enryption? */
	fil_encryption_t mode= FIL_ENCRYPTION_OFF;
	fil_space_crypt_t* crypt_data= nullptr;

	/* We created the binlog file and now write it full of zeros */
	if (!os_file_set_size(name, fh,
			      os_offset_t{size} << srv_page_size_shift)) {
		ib::error() << "Unable to allocate " << name;
		os_file_close(fh);
		os_file_delete(innodb_data_file_key, name);
		return DB_ERROR;
	}

	mysql_mutex_lock(&fil_system.mutex);
        /* ToDo: Need to ensure file (N-2) is no longer active before creating (N). */
	uint32_t space_id= SRV_SPACE_ID_BINLOG0 + (file_no & 1);
	if (!(*new_space= fil_space_t::create(space_id,
                                                ( FSP_FLAGS_FCRC32_MASK_MARKER |
						  FSP_FLAGS_FCRC32_PAGE_SSIZE()),
						FIL_TYPE_TABLESPACE, crypt_data,
						mode, true))) {
		mysql_mutex_unlock(&fil_system.mutex);
		os_file_close(fh);
		os_file_delete(innodb_data_file_key, name);
		return DB_ERROR;
	}

	fil_node_t* node = (*new_space)->add(name, fh, size, false, true);
	IF_WIN(node->find_metadata(), node->find_metadata(fh, true));
	mysql_mutex_unlock(&fil_system.mutex);

	return DB_SUCCESS;
}


/*
  Background thread to close old binlog tablespaces and pre-allocate new ones.
*/
static void
fsp_binlog_prealloc_thread()
{

  mysql_mutex_lock(&active_binlog_mutex);
  while (1)
  {
    uint64_t active= active_binlog_file_no.load(std::memory_order_relaxed);
    uint64_t first_open= first_open_binlog_file_no.load(std::memory_order_relaxed);

    /* Pre-allocate the next tablespace (if not done already). */
    uint64_t last_created= last_created_binlog_file_no;
    if (last_created <= active && last_created <= first_open) {
      fil_space_t *new_space;
      ut_ad(last_created == active);
      ut_ad(last_created == first_open || first_open == ~(uint64_t)0);
      /*
        Note: `last_created` is initialized to ~0, so incrementing it here
        makes us start from binlog file 0.
      */
      ++last_created;
      mysql_mutex_unlock(&active_binlog_mutex);
      dberr_t res2= fsp_binlog_tablespace_create(last_created, &new_space);
      mysql_mutex_lock(&active_binlog_mutex);
      ut_a(res2 == DB_SUCCESS /* ToDo: Error handling. */);
      ut_a(new_space);
      last_created_binlog_file_no= last_created;
      last_created_binlog_space= new_space;

      /* If we created the initial tablespace file, make it the active one. */
      ut_ad(active < ~(uint64_t)0 || last_created == 0);
      if (active == ~(uint64_t)0) {
        active_binlog_file_no.store(last_created, std::memory_order_relaxed);
        active_binlog_space= last_created_binlog_space;
      }
      if (first_open == ~(uint64_t)0)
        first_open_binlog_file_no.store(first_open= last_created,
                                        std::memory_order_relaxed);

      pthread_cond_signal(&active_binlog_cond);
      continue;  /* Re-start loop after releasing/reacquiring mutex. */
    }

    /*
      Flush out to disk and close any binlog tablespace that has been
      completely written.
    */
    if (first_open < active) {
      ut_ad(first_open == active - 1);
      mysql_mutex_unlock(&active_binlog_mutex);
      fsp_binlog_tablespace_close(active - 1);
      mysql_mutex_lock(&active_binlog_mutex);
      first_open_binlog_file_no.store(first_open + 1, std::memory_order_relaxed);
      continue;  /* Re-start loop after releasing/reacquiring mutex. */
    }

    /* Exit thread at server shutdown. */
    if (prealloc_thread_end)
      break;
    my_cond_wait(&active_binlog_cond, &active_binlog_mutex.m_mutex);

  }
  mysql_mutex_unlock(&active_binlog_mutex);
}


void fsp_binlog_write_start(uint32_t page_no,
                            const uchar *data, uint32_t len, mtr_t *mtr)
{
	buf_block_t *block= fsp_page_create(active_binlog_space, page_no, mtr);
	mtr->memcpy<mtr_t::MAYBE_NOP>(*block, FIL_PAGE_DATA + block->page.frame,
				      data, len);
	binlog_cur_block= block;
}

void fsp_binlog_write_offset(uint32_t page_no, uint32_t offset,
                             const uchar *data, uint32_t len, mtr_t *mtr)
{
	dberr_t err;
        /* ToDo: Is RW_SX_LATCH appropriate here? */
	buf_block_t *block= buf_page_get_gen(page_id_t{active_binlog_space->id, page_no},
					     0, RW_SX_LATCH, binlog_cur_block,
					     BUF_GET, mtr, &err);
	ut_a(err == DB_SUCCESS);
	mtr->memcpy<mtr_t::MAYBE_NOP>(*block,
                                      offset + block->page.frame,
                                      data, len);
}

void fsp_binlog_append(const uchar *data, uint32_t len, mtr_t *mtr)
{
  ut_ad(binlog_cur_page_offset <= srv_page_size - FIL_PAGE_DATA_END);
  uint32_t remain= ((uint32_t)srv_page_size - FIL_PAGE_DATA_END) -
    binlog_cur_page_offset;
  // ToDo: Some kind of mutex to protect binlog access.
  while (len > 0) {
    if (remain < 4) {
      binlog_cur_page_offset= FIL_PAGE_DATA;
      remain= ((uint32_t)srv_page_size - FIL_PAGE_DATA_END) -
        binlog_cur_page_offset;
      ++binlog_cur_page_no;
    }
    uint32_t this_len= std::min<uint32_t>(len, remain);
    if (binlog_cur_page_offset == FIL_PAGE_DATA)
      fsp_binlog_write_start(binlog_cur_page_no, data, this_len, mtr);
    else
      fsp_binlog_write_offset(binlog_cur_page_no, binlog_cur_page_offset,
                              data, this_len, mtr);
    len-= this_len;
    data+= this_len;
    binlog_cur_page_offset+= this_len;
  }
}

void fsp_binlog_write_cache(IO_CACHE *cache, size_t main_size, mtr_t *mtr)
{
  uint32_t page_size= (uint32_t)srv_page_size;
  uint32_t page_size_shift= srv_page_size_shift;
  fil_space_t *space= active_binlog_space;
  const uint32_t page_end= page_size - FIL_PAGE_DATA_END;
  uint32_t page_no= binlog_cur_page_no;
  uint32_t page_offset= binlog_cur_page_offset;
  /* ToDo: What is the lifetime of what's pointed to by binlog_cur_block, is there some locking needed around it or something? */
  buf_block_t *block= binlog_cur_block;
  uint64_t file_no= active_binlog_file_no.load(std::memory_order_relaxed);
  uint64_t pending_prev_end_offset= 0;

  /*
    Write out the event data in chunks of whatever size will fit in the current
    page, until all data has been written.
  */
  size_t remain= my_b_tell(cache);
  ut_ad(remain > main_size);
  if (cache->pos_in_file > 0) {
    /*
      ToDo: A limitation in mysys IO_CACHE. If I change (reinit_io_cache())
      the cache from WRITE_CACHE to READ_CACHE without seeking out of the
      current buffer, then the cache will not be flushed to disk (which is
      good for small cache that fits completely in buffer). But then if I
      later my_b_seek() or reinit_io_cache() it again and seek out of the
      current buffer, the buffered data will not be flushed to the file
      because the cache is now a READ_CACHE! The result is that the end of the
      cache will be lost if the cache doesn't fit in memory.

      So for now, have to do this somewhat in-elegant conditional flush
      myself.
    */
    flush_io_cache(cache);
  }
  /* Start with the GTID event, which is put at the end of the IO_CACHE. */
  my_bool res= reinit_io_cache(cache, READ_CACHE, main_size, 0, 0);
  ut_a(!res /* ToDo: Error handling. */);
  size_t gtid_remain= remain - main_size;
  while (remain > 0) {
    if (page_offset == FIL_PAGE_DATA) {
      if (UNIV_UNLIKELY(page_no >= space->size)) {
        /*
          Signal to the pre-allocation thread that this tablespace has been
          written full, so that it can be closed and a new one pre-allocated
          in its place. Then wait for a new tablespace to be pre-allocated that
          we can use.

          The normal case is that the next tablespace is already pre-allocated
          and available; binlog tablespace N is active while (N+1) is being
          pre-allocated. Only under extreme I/O pressure should be need to
          stall here.

          ToDo: Handle recovery. Idea: write the current LSN at the start of
          the binlog tablespace when we create it. At recovery, we should open
          the (at most) 2 most recent binlog tablespaces. Whenever we have a
          redo record, skip it if its LSN is smaller than the one stored in the
          tablespace corresponding to its space_id. This way, it should be safe
          to re-use tablespace ids between just two, SRV_SPACE_ID_BINLOG0 and
          SRV_SPACE_ID_BINLOG1.
        */
        pending_prev_end_offset= page_no << page_size_shift;
        mysql_mutex_lock(&active_binlog_mutex);
        /* ToDo: Make this wait killable?. */
        /* ToDo2: Handle not stalling infinitely if the new tablespace cannot be created due to eg. I/O error. Or should we in this case loop and repeatedly retry the create? */
        while (last_created_binlog_file_no <= file_no) {
          my_cond_wait(&active_binlog_cond, &active_binlog_mutex.m_mutex);
        }

        // ToDo: assert that a single write doesn't span more than two binlog files.
        ++file_no;
        binlog_cur_written_offset[file_no & 1].store(0, std::memory_order_relaxed);
        binlog_cur_end_offset[file_no & 1].store(0, std::memory_order_relaxed);
        active_binlog_file_no.store(file_no, std::memory_order_release);
        active_binlog_space= space= last_created_binlog_space;
        pthread_cond_signal(&active_binlog_cond);
        mysql_mutex_unlock(&active_binlog_mutex);
        binlog_cur_page_no= page_no= 0;
      }
      block= fsp_page_create(space, page_no, mtr);
    } else {
      dberr_t err;
      /* ToDo: Is RW_SX_LATCH appropriate here? */
      block= buf_page_get_gen(page_id_t{space->id, page_no},
                              0, RW_SX_LATCH, block,
                              BUF_GET, mtr, &err);
      ut_a(err == DB_SUCCESS);
    }

    ut_ad(page_offset < page_end);
    uint32_t page_remain= page_end - page_offset;
    byte *ptr= page_offset + block->page.frame;
    /* ToDo: Do this check at the end instead, to save one buf_page_get_gen()? */
    if (page_remain < 4) {
      /* Pad the remaining few bytes, and move to next page. */
      mtr->memset(block, page_offset, page_remain, 0xff);
      block= nullptr;
      ++page_no;
      page_offset= FIL_PAGE_DATA;
      continue;
    }
    page_remain-= 3;    /* Type byte and 2-byte length. */
    uint32_t size= 0;
    /* Write GTID data, if any still available. */
    if (gtid_remain > 0)
    {
      size= gtid_remain > page_remain ? page_remain : (uint32_t)gtid_remain;
      int res2= my_b_read(cache, ptr+3, size);
      ut_a(!res2 /* ToDo: Error handling */);
      gtid_remain-= size;
      page_remain-= size;
      if (gtid_remain == 0)
        my_b_seek(cache, 0);    /* Move to read the rest of the events. */
    }
    /* Write remaining data, if any available _and_ more room on page. */
    ut_ad(remain >= size);
    size_t remain2= remain - size;
    if (remain2 + page_remain > 0) {
      uint32_t size2= remain2 > page_remain ? page_remain : (uint32_t)remain2;
      int res2= my_b_read(cache, ptr+3+size, size2);
      ut_a(!res2 /* ToDo: Error handling */);
      size+= size2;
      page_remain-= size2;
    }
    ptr[0]= 0x01 /* ToDo: FSP_BINLOG_TYPE_COMMIT */ | ((size < remain) << 7);
    ptr[1]= size & 0xff;
    ptr[2]= (byte)(size >> 8);
    ut_ad(size <= 0xffff);

    mtr->memcpy(*block, page_offset, size+3);
    remain-= size;
    if (page_remain == 0) {
      block= nullptr;
      page_offset= FIL_PAGE_DATA;
      ++page_no;
    } else {
      page_offset+= size+3;
    }
  }
  binlog_cur_block= block;
  binlog_cur_page_no= page_no;
  binlog_cur_page_offset= page_offset;
  if (UNIV_UNLIKELY(pending_prev_end_offset))
    binlog_cur_end_offset[(file_no-1) & 1].store(pending_prev_end_offset,
                                                 std::memory_order_relaxed);
  binlog_cur_end_offset[file_no & 1].store((page_no << page_size_shift) + page_offset,
                                           std::memory_order_relaxed);
}


extern "C" void binlog_get_cache(THD *, IO_CACHE **, size_t *);

void
fsp_binlog_trx(trx_t *trx, mtr_t *mtr)
{
  IO_CACHE *cache;
  size_t main_size;

  if (!trx->mysql_thd)
    return;
  binlog_get_cache(trx->mysql_thd, &cache, &main_size);
  if (main_size)
    fsp_binlog_write_cache(cache, main_size, mtr);
}


void fsp_binlog_test(const uchar *data, uint32_t len)
{
  mtr_t mtr;
  mtr.start();
  if (!active_binlog_space)
    fsp_binlog_tablespace_create(0, &active_binlog_space);
  fsp_binlog_append(data, len, &mtr);
  mtr.commit();
}


class ha_innodb_binlog_reader : public handler_binlog_reader {
  /* Buffer to hold a page read directly from the binlog file. */
  uchar *page_buf;
  /* Length of the currently open file (cur_file). */
  uint64_t cur_file_length;
  /* Used to keep track of partial chunk returned to reader. */
  uint32_t chunk_pos;
  uint32_t chunk_remain;
private:
  int read_from_buffer_pool_page(buf_block_t *block, uint64_t end_offset,
                                 uchar *buf, uint32_t len);
  int read_from_file(uint64_t end_offset, uchar *buf, uint32_t len);
  int read_from_page(uchar *page_ptr, uint64_t end_offset,
                     uchar *buf, uint32_t len);

public:
  ha_innodb_binlog_reader();
  ~ha_innodb_binlog_reader();
  virtual int read_binlog_data(uchar *buf, uint32_t len) final;
};


ha_innodb_binlog_reader::ha_innodb_binlog_reader()
  : chunk_pos(0), chunk_remain(0)
{
  page_buf= (uchar *)my_malloc(PSI_NOT_INSTRUMENTED, srv_page_size, MYF(0)); /* ToDo: InnoDB alloc function? */
  // ToDo: Need some mechanism to find where to start reading. This is just "start from 0" for early testing.
  cur_file_no= 0;
}


ha_innodb_binlog_reader::~ha_innodb_binlog_reader()
{
  if (cur_file != (File)-1)
    my_close(cur_file, MYF(0));
  my_free(page_buf); /* ToDo: InnoDB alloc function? */
}


/*
  Read data from current position in binlog.

  If the data is written to disk (visible at the OS level, even if not
  necessarily fsync()'ed to disk), we can read directly from the file.
  Otherwise, the data must still be available in the buffer pool and
  we can read it from there.

  First try a dirty read of current state; if this says the data is available
  to read from the file, this is safe to do (data cannot become un-written).

  If not, then check if the page is in the buffer pool; if not, the likewise
  we know it's safe to read from the file directly.

  Finally, do another check of the current state. This will catch the case
  where we looked for a page in binlog file N, but its tablespace id has been
  recycled, so we got a page from (N+2) instead. In this case also, we can
  then read from the real file.
*/
int ha_innodb_binlog_reader::read_binlog_data(uchar *buf, uint32_t len)
{
  int res;
  uint64_t file_no= cur_file_no;
  uint64_t offset= cur_file_offset;
  uint64_t active_file_no= active_binlog_file_no.load(std::memory_order_acquire);
  if (first_open_binlog_file_no.load(std::memory_order_relaxed) > file_no + /* Temporary hack to work-around the next line ToDo: comment */ (offset >= cur_file_length)) {
    // ToDo: I think there is a bug here, if we're at the end of active_file_no-2, we will be reading directly from active_file_no-1 without checking properly if buffer pool is needed instead. */
    return read_from_file(~(uint64_t)0, buf, len);
  }

  ut_ad(active_file_no >= file_no);
  uint32_t idx= file_no & 1;
  uint64_t write_offset=
    binlog_cur_written_offset[idx].load(std::memory_order_relaxed);
  // ToDo: I'm not 100% confident about this dirty read of the end_offset. I need to make sure it's not possible to end up using a wrong end offset when reading from a file. When reading from a file that is not the latest, active binlog file, the end offset should basically always come from the file size.
  uint64_t end_offset=
    binlog_cur_end_offset[idx].load(std::memory_order_relaxed);
  /* ToDo: Should I check end_offset? It might be stale and completely wrong? But on the other hand, I _must_ check it somehow, otherwise I might read not yet committed data (possibly never committed). But I should be able to read and check, it cannot be completely wrong, as I have the per-tablespace-id values. And in case of stale, I will then go to lock and wait and get the real value in a safe way, which also results in correct behaviour. And I can never read stale data from the file, data will not be written out until valid and synced in the redo log. */
  if (file_no == active_file_no) {
    ut_ad(end_offset >= offset);
    if (end_offset <= offset)
      return 0;
  } else {  /* file_no == active_file_no - 1 */
    if (offset >= end_offset) {  // ToDo what if this end_pos is stale? Need somehow an extra check afterwards if we are now active-2, and then do a simple file read, not EOF on the stale end_offset.
      /* Handle moving to the currently active file. */
      cur_file_no= ++file_no;
      cur_file_offset= offset= 0;
      idx= file_no & 1;
      write_offset=
        binlog_cur_written_offset[idx].load(std::memory_order_relaxed);
      end_offset=
        binlog_cur_end_offset[idx].load(std::memory_order_relaxed);
    }
  }

  if (write_offset > offset)
    return read_from_file(std::min(write_offset, end_offset), buf, len);

  /*
    The data we need may not yet been written and available to read from the
    file directly. So try to find it in the buffer pool. But don't ask the pool
    to bring in the page if it turns out not to be there, in that case we will
    just read it directly ourselves.
  */
  mtr_t mtr;
  mtr.start();
  /*
    ToDo: Here could remember last block and use as guess for the page lookup.
    This might be useful for reading at the active position in the binlog,
    where we might read successive events repeatedly from same page. Though
    there will be a (small) cost to maintaining the hint also, and we should
    clear the hint block whenever we read a page to completion. Also, care
    should be taken about the lifetime, if the hint block is required to point
    to a valid page and does not any more. */
  buf_block_t *hint_block= nullptr;
  uint32_t space_id= SRV_SPACE_ID_BINLOG0 + idx;
  uint32_t page_no= (uint32_t)(offset >> srv_page_size_shift);
  dberr_t err= DB_SUCCESS;
  buf_block_t *block=
    buf_page_get_gen(page_id_t{space_id, page_no}, 0,
                     RW_S_LATCH, hint_block, BUF_GET_IF_IN_POOL, &mtr, &err);
  if (err != DB_SUCCESS)
    res= -1;  // ToDo: More error handling here? Probably this is not expected to fail. Or what is the return if the page is not found?
  else if (!block)
    res= read_from_file(end_offset, buf, len);
  else {
    /*
      Ok, we got a page from the buffer pool. Before reading the data from it
      though, check again that the tablespace ID has not been recycled. If it
      has, then the page is invalid (it is from a newer binlog file tablespace
      file_no + 2), and we should just read from the real file directly.
    */
    active_file_no= active_binlog_file_no.load(std::memory_order_acquire);
    if (active_file_no > file_no + 1)
      res= read_from_file(~(uint64_t)0, buf, len);
    else
      res= read_from_buffer_pool_page(block, end_offset, buf, len);
  }
  mtr.commit();

  return res;
}


int
ha_innodb_binlog_reader::read_from_buffer_pool_page(buf_block_t *block,
                                                    uint64_t end_offset,
                                                    uchar *buf, uint32_t len)
{
  return read_from_page(block->page.frame, end_offset, buf, len);
}


int
ha_innodb_binlog_reader::read_from_file(uint64_t end_offset,
                                        uchar *buf, uint32_t len)
{
  uint64_t mask= ((uint64_t)1 << srv_page_size_shift) - 1;
  uint64_t offset= cur_file_offset;
  uint64_t page_start_offset;

  if (cur_file < (File)0 || cur_file_offset >= cur_file_length) {
    if (!(cur_file < (File)0)) {
      my_close(cur_file, MYF(0));
      ++cur_file_no;
    }
    char filename[BINLOG_NAME_LEN];
    binlog_name_make(filename, cur_file_no);
    if ((cur_file= my_open(filename, O_RDONLY | O_BINARY, MYF(MY_WME))) < (File)0)
      return -1;
    /* ToDo: Handle closing the file when we reach the end. In fact, handle reaching the end of a file in the first place. */
    MY_STAT stat_buf;
    if (my_fstat(cur_file, &stat_buf, MYF(0))) {
      my_error(ER_CANT_GET_STAT, MYF(0), filename, errno);
      my_close(cur_file, MYF(0));
      cur_file= (File)-1;
      return -1;
    }
    cur_file_length= stat_buf.st_size;
    cur_file_offset= offset= 0;
  }

  page_start_offset= offset & ~mask;
  size_t res= my_pread(cur_file, page_buf, srv_page_size, page_start_offset,
                       MYF(MY_WME));
  if (res == (size_t)-1)
    return -1;

  return read_from_page(page_buf, end_offset, buf, len);
}


/*
  Read out max `len` bytes from the chunks stored in a page.

  page_ptr   Points to start of data for current page matching cur_file_offset
  end_offset Current end of binlog file, no reads past this point
  buf        Destination buffer to read into
  len        Maximum number of bytes to read

  Returns number of bytes actually read.
*/
int
ha_innodb_binlog_reader::read_from_page(uchar *page_ptr, uint64_t end_offset,
                                        uchar *buf, uint32_t len)
{
  uint32_t page_size= (uint32_t)srv_page_size;
  uint64_t mask= ((uint64_t)1 << srv_page_size_shift) - 1;
  uint64_t offset= cur_file_offset;
  uint64_t page_start_offset= offset & ~mask;
  uint32_t page_end=
    end_offset > page_start_offset + (page_size - FIL_PAGE_DATA_END) ?
      (page_size - FIL_PAGE_DATA_END) :
      (uint32_t)(end_offset & mask);
  uint32_t in_page_offset= (uint32_t)(offset & mask);
  uint32_t sofar= 0;

  ut_ad(in_page_offset < page_size - FIL_PAGE_DATA_END);
  if (in_page_offset < FIL_PAGE_DATA)
    in_page_offset= FIL_PAGE_DATA;

  /* First return data from any partially-read chunk. */
  if ((sofar= chunk_remain)) {
    if (sofar <= len) {
      memcpy(buf, page_ptr + in_page_offset + chunk_pos, sofar);
      chunk_pos= 0;
      chunk_remain= 0;
      in_page_offset+= sofar;
    } else {
      memcpy(buf, page_ptr + in_page_offset + chunk_pos, len);
      chunk_pos+= len;
      chunk_remain= sofar - len;
      cur_file_offset= offset + len;
      return len;
    }
  }

  while (sofar < len && in_page_offset < page_end)
  {
    uchar type= page_ptr[in_page_offset];
    if (type == 0x00)
      break;  /* No more data on the page yet */
    if (type == 0xff /* ToDo FSP_BINLOG_TYPE_FILLER */) {
      in_page_offset= page_size;  /* Point to start of next page */
      break;  /* No more data on page */
    }
    uint32_t size=
      page_ptr[in_page_offset + 1] + (uint32_t)(page_ptr[in_page_offset + 2] << 8);
    if ((type & 0x7f) != 1 /* ToDo FSP_BINLOG_TYPE_COMMIT */) {
      /* Skip non-binlog-event record. */
      in_page_offset += 3 + size;
      continue;
    }

    /* Now grab the data in the chunk, or however much the caller requested. */
    uint32_t rest = len - sofar;
    if (size > rest) {
      /*
        Chunk contains more data than reader requested.
        Return what was requested, and remember the remaining partial data
        for the next read.
      */
      memcpy(buf + sofar, page_ptr + (in_page_offset + 3), rest);
      chunk_pos= rest;
      chunk_remain= size - rest;
      sofar+= rest;
      break;
    }

    memcpy(buf + sofar, page_ptr + (in_page_offset + 3), size);
    in_page_offset= in_page_offset + 3 + size;
    sofar+= size;
  }

  if (in_page_offset >= page_size - FIL_PAGE_DATA_END)
    cur_file_offset= page_start_offset + page_size; // To start of next page
  else
    cur_file_offset= page_start_offset | in_page_offset;
  return sofar;
}


handler_binlog_reader *
innodb_get_binlog_reader()
{
  return new ha_innodb_binlog_reader();
}


bool
innobase_binlog_write_direct(IO_CACHE *cache, size_t main_size)
{
  mtr_t mtr;
  mtr.start();
  fsp_binlog_write_cache(cache, main_size, &mtr);
  mtr.commit();
  /* ToDo: Should we sync the log here? Maybe depending on an extra bool parameter? */
  /* ToDo: Presumably fsp_binlog_write_cache() should be able to fail in some cases? Then return any such error to the caller. */
  return false;
}