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Date:   Fri, 28 Feb 2020 11:59:54 -0800
From:   Matthew Wilcox <willy@infradead.org>
To:     Goldwyn Rodrigues <rgoldwyn@suse.com>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Ritesh Harjani <riteshh@linux.ibm.com>,
        linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        darrick.wong@oracle.com
Subject: Re: [PATCH v2] iomap: return partial I/O count on error in
 iomap_dio_bio_actor
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On Fri, Feb 28, 2020 at 01:44:01PM -0600, Goldwyn Rodrigues wrote:
> +++ 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;

There's another change here ... look at the out label

out:
        /* Undo iter limitation to current extent */
        iov_iter_reexpand(dio->submit.iter, orig_count - copied);
        if (copied)
                return copied;
        return ret;

so you're also changing by how much the iter is reexpanded.  I
don't know if it's the appropriate amount; I still don't quite get the
iov_iter complexities.