btrfs: convert read_key_bytes() to take a folio

The old page API is being gradually replaced and converted to use folio
to improve code readability and avoid repeated conversion between page
and folio. Moreover, use kmap_local_folio() instead of kmap_local_page(),
which is more consistent with folio usage.
Signed-off-by: Li Zetao <lizetao1@huawei.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/verity.c

@@ -284,7 +284,7 @@ static int write_key_bytes(struct btrfs_inode *inode, u8 key_type, u64 offset,
  *              page and ignore dest, but it must still be non-NULL to avoid the
  *              counting-only behavior.
  * @len:        length in bytes to read
- * @dest_page:  copy into this page instead of the dest buffer
+ * @dest_folio: copy into this folio instead of the dest buffer
  *
  * Helper function to read items from the btree.  This returns the number of
  * bytes read or < 0 for errors.  We can return short reads if the items don't
@@ -294,7 +294,7 @@ static int write_key_bytes(struct btrfs_inode *inode, u8 key_type, u64 offset,
  * Returns number of bytes read or a negative error code on failure.
  */
 static int read_key_bytes(struct btrfs_inode *inode, u8 key_type, u64 offset,
-			  char *dest, u64 len, struct page *dest_page)
+			  char *dest, u64 len, struct folio *dest_folio)
 {
 	struct btrfs_path *path;
 	struct btrfs_root *root = inode->root;
@@ -314,7 +314,7 @@ static int read_key_bytes(struct btrfs_inode *inode, u8 key_type, u64 offset,
 	if (!path)
 		return -ENOMEM;
 
-	if (dest_page)
+	if (dest_folio)
 		path->reada = READA_FORWARD;
 
 	key.objectid = btrfs_ino(inode);
@@ -371,15 +371,15 @@ static int read_key_bytes(struct btrfs_inode *inode, u8 key_type, u64 offset,
 		copy_offset = offset - key.offset;
 
 		if (dest) {
-			if (dest_page)
-				kaddr = kmap_local_page(dest_page);
+			if (dest_folio)
+				kaddr = kmap_local_folio(dest_folio, 0);
 
 			data = btrfs_item_ptr(leaf, path->slots[0], void);
 			read_extent_buffer(leaf, kaddr + dest_offset,
 					   (unsigned long)data + copy_offset,
 					   copy_bytes);
 
-			if (dest_page)
+			if (dest_folio)
 				kunmap_local(kaddr);
 		}
 
@@ -762,7 +762,7 @@ static struct page *btrfs_read_merkle_tree_page(struct inode *inode,
 	 * [ inode objectid, BTRFS_MERKLE_ITEM_KEY, offset in bytes ]
 	 */
 	ret = read_key_bytes(BTRFS_I(inode), BTRFS_VERITY_MERKLE_ITEM_KEY, off,
-			     folio_address(folio), PAGE_SIZE, &folio->page);
+			     folio_address(folio), PAGE_SIZE, folio);
 	if (ret < 0) {
 		folio_put(folio);
 		return ERR_PTR(ret);