btrfs: add helpers to get fs_info from page/folio pointers

Add convenience helpers to get a fs_info from a page or folio pointer
instead of open coding the chain or using btrfs_sb() that in some cases
does one more pointer hop.  This is implemented as a macro (still with
type checking) so we don't need full definitions of struct page, folio,
btrfs_root and btrfs_fs_info. The latter can't be static inlines as this
would create loop between ctree.h <-> fs.h, or the headers would have to
be restructured.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/compression.c

@@ -1036,7 +1036,7 @@ static int btrfs_decompress_bio(struct compressed_bio *cb)
 int btrfs_decompress(int type, const u8 *data_in, struct page *dest_page,
 		     unsigned long dest_pgoff, size_t srclen, size_t destlen)
 {
-	struct btrfs_fs_info *fs_info = btrfs_sb(dest_page->mapping->host->i_sb);
+	struct btrfs_fs_info *fs_info = page_to_fs_info(dest_page);
 	struct list_head *workspace;
 	const u32 sectorsize = fs_info->sectorsize;
 	int ret;

fs/btrfs/disk-io.c

@@ -533,7 +533,7 @@ static void btree_invalidate_folio(struct folio *folio, size_t offset,
 	extent_invalidate_folio(tree, folio, offset);
 	btree_release_folio(folio, GFP_NOFS);
 	if (folio_get_private(folio)) {
-		btrfs_warn(BTRFS_I(folio->mapping->host)->root->fs_info,
+		btrfs_warn(folio_to_fs_info(folio),
 			   "folio private not zero on folio %llu",
 			   (unsigned long long)folio_pos(folio));
 		folio_detach_private(folio);

fs/btrfs/extent_io.c

@@ -432,7 +432,7 @@ static bool btrfs_verify_page(struct page *page, u64 start)
 
 static void end_page_read(struct page *page, bool uptodate, u64 start, u32 len)
 {
-	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
+	struct btrfs_fs_info *fs_info = page_to_fs_info(page);
 	struct folio *folio = page_folio(page);
 
 	ASSERT(page_offset(page) <= start &&
@@ -940,7 +940,7 @@ int set_folio_extent_mapped(struct folio *folio)
 	if (folio_test_private(folio))
 		return 0;
 
-	fs_info = btrfs_sb(folio->mapping->host->i_sb);
+	fs_info = folio_to_fs_info(folio);
 
 	if (btrfs_is_subpage(fs_info, folio->mapping))
 		return btrfs_attach_subpage(fs_info, folio, BTRFS_SUBPAGE_DATA);
@@ -959,7 +959,7 @@ void clear_page_extent_mapped(struct page *page)
 	if (!folio_test_private(folio))
 		return;
 
-	fs_info = btrfs_sb(page->mapping->host->i_sb);
+	fs_info = page_to_fs_info(page);
 	if (btrfs_is_subpage(fs_info, page->mapping))
 		return btrfs_detach_subpage(fs_info, folio);
 
@@ -1760,7 +1760,7 @@ static noinline_for_stack void write_one_eb(struct extent_buffer *eb,
  */
 static int submit_eb_subpage(struct page *page, struct writeback_control *wbc)
 {
-	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
+	struct btrfs_fs_info *fs_info = page_to_fs_info(page);
 	struct folio *folio = page_folio(page);
 	int submitted = 0;
 	u64 page_start = page_offset(page);
@@ -1851,7 +1851,7 @@ static int submit_eb_page(struct page *page, struct btrfs_eb_write_context *ctx)
 	if (!folio_test_private(folio))
 		return 0;
 
-	if (btrfs_sb(page->mapping->host->i_sb)->nodesize < PAGE_SIZE)
+	if (page_to_fs_info(page)->nodesize < PAGE_SIZE)
 		return submit_eb_subpage(page, wbc);
 
 	spin_lock(&mapping->i_private_lock);
@@ -2303,7 +2303,7 @@ int extent_invalidate_folio(struct extent_io_tree *tree,
 	struct extent_state *cached_state = NULL;
 	u64 start = folio_pos(folio);
 	u64 end = start + folio_size(folio) - 1;
-	size_t blocksize = btrfs_sb(folio->mapping->host->i_sb)->sectorsize;
+	size_t blocksize = folio_to_fs_info(folio)->sectorsize;
 
 	/* This function is only called for the btree inode */
 	ASSERT(tree->owner == IO_TREE_BTREE_INODE_IO);
@@ -4833,7 +4833,7 @@ static struct extent_buffer *get_next_extent_buffer(
 
 static int try_release_subpage_extent_buffer(struct page *page)
 {
-	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
+	struct btrfs_fs_info *fs_info = page_to_fs_info(page);
 	u64 cur = page_offset(page);
 	const u64 end = page_offset(page) + PAGE_SIZE;
 	int ret;
@@ -4906,7 +4906,7 @@ int try_release_extent_buffer(struct page *page)
 	struct folio *folio = page_folio(page);
 	struct extent_buffer *eb;
 
-	if (btrfs_sb(page->mapping->host->i_sb)->nodesize < PAGE_SIZE)
+	if (page_to_fs_info(page)->nodesize < PAGE_SIZE)
 		return try_release_subpage_extent_buffer(page);
 
 	/*

fs/btrfs/fs.h

@@ -836,6 +836,9 @@ struct btrfs_fs_info {
 #define folio_to_inode(_folio)	(BTRFS_I(_Generic((_folio),			\
 					  struct folio *: (_folio))->mapping->host))
 
+#define page_to_fs_info(_page)	 (page_to_inode(_page)->root->fs_info)
+#define folio_to_fs_info(_folio) (folio_to_inode(_folio)->root->fs_info)
+
 static inline u64 btrfs_get_fs_generation(const struct btrfs_fs_info *fs_info)
 {
 	return READ_ONCE(fs_info->generation);

fs/btrfs/inode.c

@@ -7904,7 +7904,7 @@ static void btrfs_readahead(struct readahead_control *rac)
  */
 static void wait_subpage_spinlock(struct page *page)
 {
-	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
+	struct btrfs_fs_info *fs_info = page_to_fs_info(page);
 	struct folio *folio = page_folio(page);
 	struct btrfs_subpage *subpage;
 

fs/btrfs/lzo.c

@@ -429,7 +429,7 @@ int lzo_decompress(struct list_head *ws, const u8 *data_in,
 		size_t destlen)
 {
 	struct workspace *workspace = list_entry(ws, struct workspace, list);
-	struct btrfs_fs_info *fs_info = btrfs_sb(dest_page->mapping->host->i_sb);
+	struct btrfs_fs_info *fs_info = page_to_fs_info(dest_page);
 	const u32 sectorsize = fs_info->sectorsize;
 	size_t in_len;
 	size_t out_len;