linux-ext4 - Re: ll_ver_fs data verification failure

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Date:	Thu, 06 Aug 2009 17:28:08 -0400
From:	Nick Dokos <nicholas.dokos@...com>
To:	Andreas Dilger <adilger@....com>
Cc:	Nick Dokos <nicholas.dokos@...com>,
	Valerie Aurora <vaurora@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: ll_ver_fs data verification failure - 96TB fs 

> On Aug 06, 2009  16:37 -0400, Nick Dokos wrote:
> > I did that to begin with but the problem turns out to be much more
> > mundane: there was an IO error on one of the volumes. It wasn't quite
> > obvious (no red lights going off) but there *was* a message in
> > /var/log/messages - unfortunately I missed it. I eventually recreated
> > the error by trying to read the file with ``od -c'' and then went back
> > and found the original error. I don't know why/how ll_ver_fs managed to
> > read the offset and come up with a 1M difference[1] -- ``od -c'' failed with
> > a big thud.
> 
> 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.

Thanks,
Nick



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