Hi,
Jeffrey J. Kosowsky wrote on 2011-10-06 22:09:52 -0400 [Re: [BackupPC-users]
Bad md5sums due to zero size (uncompressed) cpool files - WEIRD BUG]:
> Holger Parplies wrote at about 02:45:56 +0200 on Friday, October 7, 2011:
> > Jeffrey J. Kosowsky wrote on 2011-10-06 19:28:38 -0400 [Re:
> [BackupPC-users] Bad md5sums due to zero size (uncompressed)?cpool files -
> WEIRD BUG]:
> > >
> > > Actually this could be made even faster since there seem to be 2
> > > cases:
> > > 1. Files of length 8 bytes with first byte = 78 [no rsync checksums]
> > > 2. Files of length 57 bytes with first byte = d7 [rsync checksums]
> > >
> > > So, all you need to do is to stat the size and then test the
> > > first-byte
> > [...]
> > An additionally running 'find' does report some 57-byte files, but they
> > don't seem to decompress to "".
>
> Do those 57 byte files have rsync checksums or are they just
> compressed files that happen to be 57 bytes long?
well, I implemented your suggestion quoted above to determine whether they
would decompress empty, so they are just compressed files that happen to be 57
bytes long. Actually, I included a debug option to output 57 byte files
with a first byte \x78, and they seem to show up there (I didn't check if all
do, I was only interested in checking my implementation).
My point was that 'find cpool \( -size 8c -o -size 57c \)' does show quite a
number of hits - so many that it's hard to see whether there are any 8-byte
files in between - and the 57-byte ones are pointless, because you'd have to
individually determine whether they are just compressed files that happen to
be 57 bytes long or empty compressed files with checksums. I simply hadn't
expected that. 'find cpool -size 8c' should still be useful as a lightweight
check for your first case.
> Given that the rsync checksums have both block and file checksums,
> it's hard to believe that a 57 byte file including rsync checksums
> would have much if any data.
I thought you were positive that it can't. Actually, your reasoning seems to
say that it can't, but what about an 8-byte file without checksums? There's
not much point in looking for 8-byte files with a \x78 if it's uncertain that
they're really empty - at least we'd need to decompress to check.
Regards,
Holger
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