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Date:   Mon, 13 Dec 2021 08:38:08 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Christoph Hellwig <hch@lst.de>, dan.j.williams@intel.com,
        linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
        nvdimm@lists.linux.dev, Dan Carpenter <dan.carpenter@oracle.com>
Subject: Re: [PATCH] iomap: turn the byte variable in iomap_zero_iter into
 a ssize_t
Message-ID: <20211213073808.GA20684@lst.de>
References: <20211208091203.2927754-1-hch@lst.de> <YbTk+1I4VFQpgjM/@casper.infradead.org>
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On Sat, Dec 11, 2021 at 05:50:51PM +0000, Matthew Wilcox wrote:
> On Wed, Dec 08, 2021 at 10:12:03AM +0100, Christoph Hellwig wrote:
> > bytes also hold the return value from iomap_write_end, which can contain
> > a negative error value.  As bytes is always less than the page size even
> > the signed type can hold the entire possible range.
> 
> iomap_write_end() can't return an errno.  I went through and checked as
> part of the folio conversion.  It actually has two return values -- 0
> on error and 'len' on success.  And it can't have an error because
> that only occurs if 'copied' is less than 'length'.
> 
> So I think this should actually be:
> 
> -               bytes = iomap_write_end(iter, pos, bytes, bytes, folio);
> -               if (bytes < 0)
> -                       return bytes;
> +               status = iomap_write_end(iter, pos, bytes, bytes, folio);
> +               if (WARN_ON_ONCE(status == 0))
> +                       return -EIO;
> 
> just like its counterpart loop in iomap_unshare_iter()
> 
> (ok this won't apply to Dan's tree, but YKWIM)

Indeed.  It might make sense to eventually switch to actually return
an errno or a bool as the current calling convention is rather confusing.