ocfs2: convert ocfs2_map_page_blocks to use a folio

Convert the page argument to a folio and then use the folio APIs
throughout.  Replaces three hidden calls to compound_head() with one
explicit one.

Link: https://lkml.kernel.org/r/20231016201114.1928083-22-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Pankaj Raghav <p.raghav@samsung.com>
Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/ocfs2/aops.c

@@ -568,10 +568,10 @@ static void ocfs2_clear_page_regions(struct page *page,
  * read-in the blocks at the tail of our file. Avoid reading them by
  * testing i_size against each block offset.
  */
-static int ocfs2_should_read_blk(struct inode *inode, struct page *page,
+static int ocfs2_should_read_blk(struct inode *inode, struct folio *folio,
 				 unsigned int block_start)
 {
-	u64 offset = page_offset(page) + block_start;
+	u64 offset = folio_pos(folio) + block_start;
 
 	if (ocfs2_sparse_alloc(OCFS2_SB(inode->i_sb)))
 		return 1;
@@ -593,15 +593,16 @@ int ocfs2_map_page_blocks(struct page *page, u64 *p_blkno,
 			  struct inode *inode, unsigned int from,
 			  unsigned int to, int new)
 {
+	struct folio *folio = page_folio(page);
 	int ret = 0;
 	struct buffer_head *head, *bh, *wait[2], **wait_bh = wait;
 	unsigned int block_end, block_start;
 	unsigned int bsize = i_blocksize(inode);
 
-	if (!page_has_buffers(page))
-		create_empty_buffers(page, bsize, 0);
+	head = folio_buffers(folio);
+	if (!head)
+		head = folio_create_empty_buffers(folio, bsize, 0);
 
-	head = page_buffers(page);
 	for (bh = head, block_start = 0; bh != head || !block_start;
 	     bh = bh->b_this_page, block_start += bsize) {
 		block_end = block_start + bsize;
@@ -613,7 +614,7 @@ int ocfs2_map_page_blocks(struct page *page, u64 *p_blkno,
 		 * they may belong to unallocated clusters.
 		 */
 		if (block_start >= to || block_end <= from) {
-			if (PageUptodate(page))
+			if (folio_test_uptodate(folio))
 				set_buffer_uptodate(bh);
 			continue;
 		}
@@ -630,11 +631,11 @@ int ocfs2_map_page_blocks(struct page *page, u64 *p_blkno,
 			clean_bdev_bh_alias(bh);
 		}
 
-		if (PageUptodate(page)) {
+		if (folio_test_uptodate(folio)) {
 			set_buffer_uptodate(bh);
 		} else if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
 			   !buffer_new(bh) &&
-			   ocfs2_should_read_blk(inode, page, block_start) &&
+			   ocfs2_should_read_blk(inode, folio, block_start) &&
 			   (block_start < from || block_end > to)) {
 			bh_read_nowait(bh, 0);
 			*wait_bh++=bh;
@@ -668,7 +669,7 @@ int ocfs2_map_page_blocks(struct page *page, u64 *p_blkno,
 		if (block_start >= to)
 			break;
 
-		zero_user(page, block_start, bh->b_size);
+		folio_zero_range(folio, block_start, bh->b_size);
 		set_buffer_uptodate(bh);
 		mark_buffer_dirty(bh);