Re: [PATCH v5 7/9] iomap: reject atomic writes in iomap_file_buffered_write()

[John Garry <john.garry@linux.dev>]

On 9/24/26 00:56, Tal Zussman wrote:
> Buffered atomic writes are not currently supported. The page cache
> writes folios back independently, so it cannot guarantee that a range is
> written atomically. iomap_file_buffered_write() does not check for
> IOCB_ATOMIC, so a direct write that falls back to it would complete an
> atomic write without atomicity. While no such case currently exists,
> fail IOCB_ATOMIC writes with -EOPNOTSUPP, so that a future fallback
> cannot complete an atomic write non-atomically.
> 
> Suggested-by: John Garry <john.garry@linux.dev>
> Signed-off-by: Tal Zussman <tz2294@columbia.edu>

Reviewed-by: John Garry <john.garry@linux.dev>

> ---
>   fs/iomap/buffered-io.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 0a5ebfda90f1..e6654cfe1cbf 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1304,6 +1304,10 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
>   	};
>   	ssize_t ret;
>   
> +	/* Buffered atomic writes are not supported */
> +	if (iocb->ki_flags & IOCB_ATOMIC)
> +		return -EOPNOTSUPP;
> +
>   	if (iocb->ki_flags & IOCB_NOWAIT)
>   		iter.flags |= IOMAP_NOWAIT;
>   	if (iocb->ki_flags & IOCB_DONTCACHE)
>