Btrfs: make free space cache write out functions more readable

This patch makes the free space cache write out functions more readable,
and beisdes that, it also reduces the stack space that the function --
__btrfs_write_out_cache uses from 194bytes to 144bytes.
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/free-space-cache.c

@@ -274,18 +274,32 @@ struct io_ctl {
 };
 
 static int io_ctl_init(struct io_ctl *io_ctl, struct inode *inode,
-		       struct btrfs_root *root)
+		       struct btrfs_root *root, int write)
 {
+	int num_pages;
+	int check_crcs = 0;
+
+	num_pages = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >>
+		    PAGE_CACHE_SHIFT;
+
+	if (btrfs_ino(inode) != BTRFS_FREE_INO_OBJECTID)
+		check_crcs = 1;
+
+	/* Make sure we can fit our crcs into the first page */
+	if (write && check_crcs &&
+	    (num_pages * sizeof(u32)) >= PAGE_CACHE_SIZE)
+		return -ENOSPC;
+
 	memset(io_ctl, 0, sizeof(struct io_ctl));
-	io_ctl->num_pages = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >>
-		PAGE_CACHE_SHIFT;
-	io_ctl->pages = kzalloc(sizeof(struct page *) * io_ctl->num_pages,
-				GFP_NOFS);
+
+	io_ctl->pages = kzalloc(sizeof(struct page *) * num_pages, GFP_NOFS);
 	if (!io_ctl->pages)
 		return -ENOMEM;
+
+	io_ctl->num_pages = num_pages;
 	io_ctl->root = root;
-	if (btrfs_ino(inode) != BTRFS_FREE_INO_OBJECTID)
-		io_ctl->check_crcs = 1;
+	io_ctl->check_crcs = check_crcs;
+
 	return 0;
 }
 
@@ -677,7 +691,7 @@ static int __load_free_space_cache(struct btrfs_root *root, struct inode *inode,
 	if (!num_entries)
 		return 0;
 
-	ret = io_ctl_init(&io_ctl, inode, root);
+	ret = io_ctl_init(&io_ctl, inode, root, 0);
 	if (ret)
 		return ret;
 
@@ -957,19 +971,18 @@ update_cache_item(struct btrfs_trans_handle *trans,
 }
 
 static noinline_for_stack int
-add_ioctl_entries(struct btrfs_root *root,
-		  struct inode *inode,
-		  struct btrfs_block_group_cache *block_group,
-		  struct io_ctl *io_ctl,
-		  struct extent_state **cached_state,
-		  struct list_head *bitmap_list,
-		  int *entries)
+write_pinned_extent_entries(struct btrfs_root *root,
+			    struct btrfs_block_group_cache *block_group,
+			    struct io_ctl *io_ctl,
+			    int *entries)
 {
 	u64 start, extent_start, extent_end, len;
-	struct list_head *pos, *n;
 	struct extent_io_tree *unpin = NULL;
 	int ret;
 
+	if (!block_group)
+		return 0;
+
 	/*
 	 * We want to add any pinned extents to our free space cache
 	 * so we don't leak the space
@@ -979,23 +992,19 @@ add_ioctl_entries(struct btrfs_root *root,
 	 */
 	unpin = root->fs_info->pinned_extents;
 
-	if (block_group)
-		start = block_group->key.objectid;
+	start = block_group->key.objectid;
 
-	while (block_group && (start < block_group->key.objectid +
-			       block_group->key.offset)) {
+	while (start < block_group->key.objectid + block_group->key.offset) {
 		ret = find_first_extent_bit(unpin, start,
 					    &extent_start, &extent_end,
 					    EXTENT_DIRTY, NULL);
-		if (ret) {
-			ret = 0;
-			break;
-		}
+		if (ret)
+			return 0;
 
 		/* This pinned extent is out of our range */
 		if (extent_start >= block_group->key.objectid +
 		    block_group->key.offset)
-			break;
+			return 0;
 
 		extent_start = max(extent_start, start);
 		extent_end = min(block_group->key.objectid +
@@ -1005,11 +1014,20 @@ add_ioctl_entries(struct btrfs_root *root,
 		*entries += 1;
 		ret = io_ctl_add_entry(io_ctl, extent_start, len, NULL);
 		if (ret)
-			goto out_nospc;
+			return -ENOSPC;
 
 		start = extent_end;
 	}
 
+	return 0;
+}
+
+static noinline_for_stack int
+write_bitmap_entries(struct io_ctl *io_ctl, struct list_head *bitmap_list)
+{
+	struct list_head *pos, *n;
+	int ret;
+
 	/* Write out the bitmaps */
 	list_for_each_safe(pos, n, bitmap_list) {
 		struct btrfs_free_space *entry =
@@ -1017,36 +1035,24 @@ add_ioctl_entries(struct btrfs_root *root,
 
 		ret = io_ctl_add_bitmap(io_ctl, entry->bitmap);
 		if (ret)
-			goto out_nospc;
+			return -ENOSPC;
 		list_del_init(&entry->list);
 	}
 
-	/* Zero out the rest of the pages just to make sure */
-	io_ctl_zero_remaining_pages(io_ctl);
-
-	ret = btrfs_dirty_pages(root, inode, io_ctl->pages, io_ctl->num_pages,
-				0, i_size_read(inode), cached_state);
-	io_ctl_drop_pages(io_ctl);
-	unlock_extent_cached(&BTRFS_I(inode)->io_tree, 0,
-			     i_size_read(inode) - 1, cached_state, GFP_NOFS);
+	return 0;
+}
 
-	if (ret)
-		goto fail;
+static int flush_dirty_cache(struct inode *inode)
+{
+	int ret;
 
 	ret = btrfs_wait_ordered_range(inode, 0, (u64)-1);
-	if (ret) {
+	if (ret)
 		clear_extent_bit(&BTRFS_I(inode)->io_tree, 0, inode->i_size - 1,
 				 EXTENT_DIRTY | EXTENT_DELALLOC, 0, 0, NULL,
 				 GFP_NOFS);
-		goto fail;
-	}
-	return 0;
 
-fail:
-	return -1;
-
-out_nospc:
-	return -ENOSPC;
+	return ret;
 }
 
 static void noinline_for_stack
@@ -1056,6 +1062,7 @@ cleanup_write_cache_enospc(struct inode *inode,
 			   struct list_head *bitmap_list)
 {
 	struct list_head *pos, *n;
+
 	list_for_each_safe(pos, n, bitmap_list) {
 		struct btrfs_free_space *entry =
 			list_entry(pos, struct btrfs_free_space, list);
@@ -1088,18 +1095,15 @@ static int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
 {
 	struct extent_state *cached_state = NULL;
 	struct io_ctl io_ctl;
-	struct list_head bitmap_list;
+	LIST_HEAD(bitmap_list);
 	int entries = 0;
 	int bitmaps = 0;
 	int ret;
-	int err = -1;
-
-	INIT_LIST_HEAD(&bitmap_list);
 
 	if (!i_size_read(inode))
 		return -1;
 
-	ret = io_ctl_init(&io_ctl, inode, root);
+	ret = io_ctl_init(&io_ctl, inode, root, 1);
 	if (ret)
 		return -1;
 
@@ -1109,42 +1113,65 @@ static int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
 	lock_extent_bits(&BTRFS_I(inode)->io_tree, 0, i_size_read(inode) - 1,
 			 0, &cached_state);
 
-
-	/* Make sure we can fit our crcs into the first page */
-	if (io_ctl.check_crcs &&
-	    (io_ctl.num_pages * sizeof(u32)) >= PAGE_CACHE_SIZE)
-		goto out_nospc;
-
 	io_ctl_set_generation(&io_ctl, trans->transid);
 
+	/* Write out the extent entries in the free space cache */
 	ret = write_cache_extent_entries(&io_ctl, ctl,
 					 block_group, &entries, &bitmaps,
 					 &bitmap_list);
 	if (ret)
 		goto out_nospc;
 
-	ret = add_ioctl_entries(root, inode, block_group, &io_ctl,
-				&cached_state, &bitmap_list, &entries);
+	/*
+	 * Some spaces that are freed in the current transaction are pinned,
+	 * they will be added into free space cache after the transaction is
+	 * committed, we shouldn't lose them.
+	 */
+	ret = write_pinned_extent_entries(root, block_group, &io_ctl, &entries);
+	if (ret)
+		goto out_nospc;
+
+	/* At last, we write out all the bitmaps. */
+	ret = write_bitmap_entries(&io_ctl, &bitmap_list);
+	if (ret)
+		goto out_nospc;
 
-	if (ret == -ENOSPC)
+	/* Zero out the rest of the pages just to make sure */
+	io_ctl_zero_remaining_pages(&io_ctl);
+
+	/* Everything is written out, now we dirty the pages in the file. */
+	ret = btrfs_dirty_pages(root, inode, io_ctl.pages, io_ctl.num_pages,
+				0, i_size_read(inode), &cached_state);
+	if (ret)
 		goto out_nospc;
-	else if (ret)
+
+	/*
+	 * Release the pages and unlock the extent, we will flush
+	 * them out later
+	 */
+	io_ctl_drop_pages(&io_ctl);
+
+	unlock_extent_cached(&BTRFS_I(inode)->io_tree, 0,
+			     i_size_read(inode) - 1, &cached_state, GFP_NOFS);
+
+	/* Flush the dirty pages in the cache file. */
+	ret = flush_dirty_cache(inode);
+	if (ret)
 		goto out;
 
-	err = update_cache_item(trans, root, inode, path, offset,
+	/* Update the cache item to tell everyone this cache file is valid. */
+	ret = update_cache_item(trans, root, inode, path, offset,
 				entries, bitmaps);
-
 out:
 	io_ctl_free(&io_ctl);
-	if (err) {
+	if (ret) {
 		invalidate_inode_pages2(inode->i_mapping);
 		BTRFS_I(inode)->generation = 0;
 	}
 	btrfs_update_inode(trans, root, inode);
-	return err;
+	return ret;
 
 out_nospc:
-
 	cleanup_write_cache_enospc(inode, &io_ctl, &cached_state, &bitmap_list);
 	goto out;
 }