Re: FOP_DONTCACHE when btrfs Direct IO fallback to buffered IO

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

> Hi,
> 
> Could we add FOP_DONTCACHE support when btrfs Direct IO fallback to buffered IO?
> 
> I noticed similar logic in zfs-2.4.0 too.
> 
> https://github.com/openzfs/zfs/releases/tag/zfs-2.4.0
> Uncached IO: Direct IO fallback to a light-weight uncached IO when unaligned
> 
> Best Regards
> Wang Yugui (wangyugui@e16-tech.com)
> 2025/12/21

The following dirty patch seems work here.

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2025/12/22


diff --git a/fs/btrfs/direct-io.c b/fs/btrfs/direct-io.c
index 802d4dbe5b38..2642dceb6911 100644
--- a/fs/btrfs/direct-io.c
+++ b/fs/btrfs/direct-io.c
@@ -881,6 +881,7 @@ ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from)
 	 */
 	if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
 		btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
+		iocb->ki_flags |= IOCB_DONTCACHE;
 		goto buffered;
 	}
 
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index fa82def46e39..64eae7417242 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -3843,7 +3843,7 @@ const struct file_operations btrfs_file_operations = {
 #endif
 	.remap_file_range = btrfs_remap_file_range,
 	.uring_cmd	= btrfs_uring_cmd,
-	.fop_flags	= FOP_BUFFER_RASYNC | FOP_BUFFER_WASYNC,
+	.fop_flags	= FOP_BUFFER_RASYNC | FOP_BUFFER_WASYNC | FOP_DONTCACHE,
 };
 
 int btrfs_fdatawrite_range(struct btrfs_inode *inode, loff_t start, loff_t end)