linux-ext4 - Re: [PATCH v2] iomap: return partial I/O count on error in iomap_dio_bio

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Date:   Fri, 21 Feb 2020 14:14:29 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Goldwyn Rodrigues <rgoldwyn@...e.com>
Cc:     linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        hch@...radead.org, darrick.wong@...cle.com
Subject: Re: [PATCH v2] iomap: return partial I/O count on error in
 iomap_dio_bio_actor

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@...e.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.