btrfs: set FMODE_CAN_ODIRECT instead of a dummy direct_IO method

Since commit a2ad63da ("VFS: add FMODE_CAN_ODIRECT file flag") file
systems can just set the FMODE_CAN_ODIRECT flag at open time instead of
wiring up a dummy direct_IO method to indicate support for direct I/O.
Do that for btrfs so that noop_direct_IO can eventually be removed.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/file.c

@@ -3700,7 +3700,8 @@ static int btrfs_file_open(struct inode *inode, struct file *filp)
 {
 	int ret;
 
-	filp->f_mode |= FMODE_NOWAIT | FMODE_BUF_RASYNC | FMODE_BUF_WASYNC;
+	filp->f_mode |= FMODE_NOWAIT | FMODE_BUF_RASYNC | FMODE_BUF_WASYNC |
+		        FMODE_CAN_ODIRECT;
 
 	ret = fsverity_file_open(inode, filp);
 	if (ret)

fs/btrfs/inode.c

@@ -11011,7 +11011,6 @@ static const struct address_space_operations btrfs_aops = {
 	.read_folio	= btrfs_read_folio,
 	.writepages	= btrfs_writepages,
 	.readahead	= btrfs_readahead,
-	.direct_IO	= noop_direct_IO,
 	.invalidate_folio = btrfs_invalidate_folio,
 	.release_folio	= btrfs_release_folio,
 	.migrate_folio	= btrfs_migrate_folio,