Re: [PATCH v2] iomap: return partial I/O count on error in iomap_dio_bio_actor

David Sterba
2020-02-21T13:14:50Z

On Thu, Feb 20, 2020 at 09:23:55AM -0600, Goldwyn Rodrigues wrote:
> In case of a block device error, written parameter in iomap_end()
> is zero as opposed to the amount of submitted I/O.
> Filesystems such as btrfs need to account for the I/O in ordered
> extents, even if it resulted in an error. Having (incomplete)
> submitted bytes in written gives the filesystem the amount of data
> which has been submitted before the error occurred, and the
> filesystem code can choose how to use it.
>
> The final returned error for iomap_dio_rw() is set by
> iomap_dio_complete().
>
> Partial writes in direct I/O are considered an error. So,
> ->iomap_end() using written == 0 as error must be changed
> to written < length. In this case, ext4 is the only user.
>
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>

> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 41c1e7c20a1f..01865db1bd09 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -264,7 +264,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
> size_t n;
> if (dio->error) {
> iov_iter_revert(dio->submit.iter, copied);
> - copied = ret = 0;
> + ret = 0;
> goto out;
> }

This part fixes problems I saw with the dio-iomap btrfs conversion
patchset, thanks.