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Subject2.6.21-git10/11: files getting truncated on xfs? or maybe an nlink problem?
I've had a couple of instances of a linux-2.6 mercurial repo getting
corrupted in some odd way this morning. It looks like files are being
truncated; not to size 0, but losing something off the end.

This is on an xfs filesystem. I haven't had any crashes/oops, and I
don't think its the normal files getting filled with 0 problem. I saw
this before the most recent set of xfs updates, but it happened again
afterwards too.

Mercurial uses a strictly append-only model for updating its repo files,
but it looks like maybe an append operation didn't stick.

I'm repulling a fresh copy of the repo; I'll be able to compare
before/after. Update: yep, definitely truncated:

$ ls -l .hg-new/store/data/_documentation/pi-futex.txt.i .hg-broken/store/data/_documentation/pi-futex.txt.i
4 -rw-rw-r-- 1 jeremy jeremy 3309 May 9 09:43 .hg-broken/store/data/_documentation/pi-futex.txt.i
4 -rw-rw-r-- 1 jeremy jeremy 3797 May 9 13:38 .hg-new/store/data/_documentation/pi-futex.txt.i

also
3476 -rw-rw-r-- 1 jeremy jeremy 3558208 May 9 13:55 00manifest.i
3476 -rw-rw-r-- 1 jeremy jeremy 3555200 May 9 09:41 00manifest.i~


where 00manifest.i~ is the broken one. The files are identical up to the
truncation point.

The repo passed "hg verify" just after I pulled it, so this corruption
came about after a while.

Hm, the other possibility is that nlinks is being misreported. When
cloning a repo, mercurial will generally hard-link files where possible,
and then break the link if it sees nlink > 1. If xfs is mis-reporting
the link count, then this will cause havok. Is that possible? Seems
unlikely, but it would also explain the symptoms. I just did a linking
clone with an older kernel, and the link count is as expected.

xfs_check passes without any output, which I presume is good.

J
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