[sheepdog] Unreliable error code handling in sheep/plainstore.c

[Roy Yang]

Maybe I miss something here.
sd_err("failed to write object %"PRIx64", path=%s, 
offset=%" PRId32 ", size=%"PRId32", result=%zd, %m", oid, path,
                        iocb->offset, iocb->length, size);

6 format positions with %, but only 5 values.
This looks a bug, and maybe the root cause why sd_err set errno?

Reset errno inside log_write will hide such errors if this is a 
real bug.
Roy

> Date: Wed, 4 Mar 2015 16:31:52 +0800
> From: namei.unix at gmail.com
> To: skypexu at gmail.com
> CC: sheepdog at lists.wpkg.org
> Subject: Re: [sheepdog] Unreliable error code handling in sheep/plainstore.c
> 
> On Wed, Mar 04, 2015 at 04:21:46PM +0800, Xu Yifeng wrote:
> > I found some unreliable error handling in plainstore.c, reason is
> > combination of
> > sd_err() and err_to_sderr(), because it is not guaranteed that
> > sd_err() does not
> > muck errno, it is possible passing an mucked errno to
> > err_to_sderr(), see following
> > code in plain_store.c, line 758:
> >    if (unlikely(size != len)) {
> >                 sd_err("failed to write object %"PRIx64", path=%s,
> > offset=%"
> >                        PRId32", size=%"PRId32", result=%zd, %m", oid, path,
> >                        iocb->offset, iocb->length, size);
> >                 ret = err_to_sderr(path, oid, errno);
> >                 goto out;
> >         }
> > 
> > it is possible that sd_err() may muck the errno, causing an
> > irrelevant errno to be passed to
> > err_to_sderr!
> 
> Good catch!
> 
> It is really a hidden bug for a long time. This might explain why I sometimes saw
> strange logs in the past!
> 
> Could you please cook a decent patch for this problem? The fix looks good to me.
> 
> Thanks,
> Yuan
> -- 
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> sheepdog at lists.wpkg.org
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