linux-ext4 - Re: ll_ver_fs data verification failure

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Message-id: <20090806221927.GI3340@webber.adilger.int>
Date:	Thu, 06 Aug 2009 16:19:27 -0600
From:	Andreas Dilger <adilger@....com>
To:	Nick Dokos <nicholas.dokos@...com>
Cc:	Valerie Aurora <vaurora@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: ll_ver_fs data verification failure - 96TB fs

On Aug 06, 2009  17:28 -0400, Nick Dokos wrote:
> > On Aug 06, 2009  16:37 -0400, Nick Dokos wrote:
> > Can you have a look at the error handling in ll_ver_fs at that point?
> > It seems that it might just have re-used the previous 1MB buffer, but
> > didn't detect/report the error from the read, which would itself be bad.
> 
> It looks right to me:
> 
> ,----
> |               ...
> | 		if (read(fd, chunk_buf, chunksize) < 0) {
> | 			fprintf(stderr, "\n%s: read %s+%llu failed: %s\n",
> | 				progname, file, offset, strerror(errno));
> | 			return 1;
> | 		}
> | 		if (verify_chunk(chunk_buf, chunksize, offset, time_st,
> | 				 inode_st, file) != 0)
> | 			return 1;
> |               ...
> `----
> 
> The read() should have failed (and I should have gotten a different error
> message) but somehow it didn't - instead, verify_chunk() was called and
> *that* detected the mismatch.

Well, it seems possible that read() returned less than chunksize bytes,
and the buffer compared correctly up to the 4kB chunk that is beyond the
read data.  That looks like a small bug in llverfs, since it is legal
for read() to return less than the requested bytes.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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