fs/buffer: convert create_page_buffers to folio_create_buffers

fs/buffer do not support large folios as there are many assumptions on the
folio size to be the host page size.  This conversion is one step towards
removing that assumption.  Also this conversion will reduce calls to
compound_head() if folio_create_buffers() calls
folio_create_empty_buffers().

Link: https://lkml.kernel.org/r/20230417123618.22094-5-p.raghav@samsung.com
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/buffer.c

@@ -1723,14 +1723,17 @@ static inline int block_size_bits(unsigned int blocksize)
 	return ilog2(blocksize);
 }
 
-static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
+static struct buffer_head *folio_create_buffers(struct folio *folio,
+						struct inode *inode,
+						unsigned int b_state)
 {
-	BUG_ON(!PageLocked(page));
+	BUG_ON(!folio_test_locked(folio));
 
-	if (!page_has_buffers(page))
-		create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
-				     b_state);
-	return page_buffers(page);
+	if (!folio_buffers(folio))
+		folio_create_empty_buffers(folio,
+					   1 << READ_ONCE(inode->i_blkbits),
+					   b_state);
+	return folio_buffers(folio);
 }
 
 /*
@@ -1774,8 +1777,8 @@ int __block_write_full_page(struct inode *inode, struct page *page,
 	int nr_underway = 0;
 	blk_opf_t write_flags = wbc_to_write_flags(wbc);
 
-	head = create_page_buffers(page, inode,
-					(1 << BH_Dirty)|(1 << BH_Uptodate));
+	head = folio_create_buffers(page_folio(page), inode,
+				    (1 << BH_Dirty) | (1 << BH_Uptodate));
 
 	/*
 	 * Be very careful.  We have no exclusion from block_dirty_folio
@@ -2038,7 +2041,7 @@ int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
 	BUG_ON(to > PAGE_SIZE);
 	BUG_ON(from > to);
 
-	head = create_page_buffers(&folio->page, inode, 0);
+	head = folio_create_buffers(folio, inode, 0);
 	blocksize = head->b_size;
 	bbits = block_size_bits(blocksize);
 
@@ -2324,7 +2327,7 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block)
 
 	VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
 
-	head = create_page_buffers(&folio->page, inode, 0);
+	head = folio_create_buffers(folio, inode, 0);
 	blocksize = head->b_size;
 	bbits = block_size_bits(blocksize);