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ext4: Do not fallback to buffered-io for DIO atomic write

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atomic writes is currently only supported for single fsblock and only
for direct-io. We should not return -ENOTBLK for atomic writes since we
want the atomic write request to either complete fully or fail
otherwise. Hence, we should never fallback to buffered-io in case of
DIO atomic write requests.
Let's also catch if this ever happens by adding some WARN_ON_ONCE before
buffered-io handling for direct-io atomic writes. More details of the
discussion [1].

While at it let's add an inline helper ext4_want_directio_fallback() which
simplifies the logic checks and inherently fixes condition on when to return
-ENOTBLK which otherwise was always returning true for any write or directio in
ext4_iomap_end(). It was ok since ext4 only supports direct-io via iomap.

[1]: https://lore.kernel.org/linux-xfs/cover.1729825985.git.ritesh.list@gmail.com/T/#m9dbecc11bed713ed0d7a486432c56b105b555f04
Suggested-by: Darrick J. Wong <djwong@kernel.org> # inline helper
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Ritesh Harjani (IBM)
2024-11-04 16:22:59 -08:00
committed by Darrick J. Wong
parent b7987a7d69
commit 299537e9df
2 changed files with 29 additions and 5 deletions
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7
fs/ext4/file.c
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@@ -599,6 +599,13 @@ out:
ssize_t err;
loff_t endbyte;
/*
* There is no support for atomic writes on buffered-io yet,
* we should never fallback to buffered-io for DIO atomic
* writes.
*/
WARN_ON_ONCE(iocb->ki_flags & IOCB_ATOMIC);
offset = iocb->ki_pos;
err = ext4_buffered_write_iter(iocb, from);
if (err < 0)