On Thu, Nov 30, 2023 at 07:23:09PM +0530, Ojaswin Mujoo wrote:
> Currently, iomap only supports atomic writes for direct IOs and there is
> no guarantees that a buffered IO will be atomic. Hence, if the user has
> explicitly requested the direct write to be atomic and there's a
> failure, return -EIO instead of falling back to buffered IO.
>
> Signed-off-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
> ---
> fs/iomap/direct-io.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 6ef25e26f1a1..3e7cd9bc8f4d 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -662,7 +662,13 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> if (ret != -EAGAIN) {
> trace_iomap_dio_invalidate_fail(inode, iomi.pos,
> iomi.len);
> - ret = -ENOTBLK;
> + /*
> + * if this write was supposed to be atomic,
> + * return the err rather than trying to fall
> + * back to buffered IO.
> + */
> + if (!atomic_write)
> + ret = -ENOTBLK;
This belongs in the caller when it receives an -ENOTBLK from
iomap_dio_rw(). The iomap code is saying "this IO cannot be done
with direct IO" by returning this value, and then the caller can
make the determination of whether to run a buffered IO or not.
For example, a filesystem might still be able to perform an atomic
IO via a COW-based buffered IO slow path. Sure, ext4 can't do this,
but the above patch would prevent filesystems that could from being
able to implement such a fallback....
-Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
