buffer: convert grow_dev_page() to use a folio

Get a folio from the page cache instead of a page, then use the folio API
throughout.  Removes a few calls to compound_head() and may be needed to
support block size > PAGE_SIZE.

Link: https://lkml.kernel.org/r/20230612210141.730128-11-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Bob Peterson <rpeterso@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/buffer.c

@@ -976,7 +976,7 @@ grow_dev_page(struct block_device *bdev, sector_t block,
 	      pgoff_t index, int size, int sizebits, gfp_t gfp)
 {
 	struct inode *inode = bdev->bd_inode;
-	struct page *page;
+	struct folio *folio;
 	struct buffer_head *bh;
 	sector_t end_block;
 	int ret = 0;
@@ -992,42 +992,38 @@ grow_dev_page(struct block_device *bdev, sector_t block,
 	 */
 	gfp_mask |= __GFP_NOFAIL;
 
-	page = find_or_create_page(inode->i_mapping, index, gfp_mask);
-
-	BUG_ON(!PageLocked(page));
+	folio = __filemap_get_folio(inode->i_mapping, index,
+			FGP_LOCK | FGP_ACCESSED | FGP_CREAT, gfp_mask);
 
-	if (page_has_buffers(page)) {
-		bh = page_buffers(page);
+	bh = folio_buffers(folio);
+	if (bh) {
 		if (bh->b_size == size) {
-			end_block = init_page_buffers(page, bdev,
+			end_block = init_page_buffers(&folio->page, bdev,
 						(sector_t)index << sizebits,
 						size);
 			goto done;
 		}
-		if (!try_to_free_buffers(page_folio(page)))
+		if (!try_to_free_buffers(folio))
 			goto failed;
 	}
 
-	/*
-	 * Allocate some buffers for this page
-	 */
-	bh = alloc_page_buffers(page, size, true);
+	bh = folio_alloc_buffers(folio, size, true);
 
 	/*
-	 * Link the page to the buffers and initialise them.  Take the
+	 * Link the folio to the buffers and initialise them.  Take the
 	 * lock to be atomic wrt __find_get_block(), which does not
-	 * run under the page lock.
+	 * run under the folio lock.
 	 */
 	spin_lock(&inode->i_mapping->private_lock);
-	link_dev_buffers(page, bh);
-	end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
-			size);
+	link_dev_buffers(&folio->page, bh);
+	end_block = init_page_buffers(&folio->page, bdev,
+			(sector_t)index << sizebits, size);
 	spin_unlock(&inode->i_mapping->private_lock);
 done:
 	ret = (block < end_block) ? 1 : -ENXIO;
 failed:
-	unlock_page(page);
-	put_page(page);
+	folio_unlock(folio);
+	folio_put(folio);
 	return ret;
 }