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SubjectQuota file format [2.3 issue]
Date
Hi!

I recently realized the format of quota.user and quota.group is both endian
and archsize dependant. I think that's very wrong, because when you have a
nicely portable ext2 filesystem on some disk and you want to move it to
another computer, you loose if you have quotas on it (in the best case
quotaon will not succeed and you won't have quotas on it, in the worst case
it will succeed and do strange things, you'll probably loose all your quota
information etc.).
Sparc64 solves this by doing userland format translation in quota utilities,
but that means it is not even possible to exchange quota enabled disks
between 32bit and 64bit SPARC boxes.
Now, what do you think about starting to use a new quota.user/quota.group
format in 2.3, which will be both endian independent and will use 64bit
values for timestamps in it (ie. change similar to old/new swap style)?
It would probably not need many kernel changes in dquot.c.
One problem is quota.user is completely header-less and in its whole size
contains data which can have any value, so it is not easy to distinguish old
format from some new one. The only thing which comes to my mind is file
size: current kernel requires quota.user (group) to be non-zero size and
some multiple of struct dqblk size. That's for sure divisible by 4. So what
about if we attach a 10 byte header before the whole data lot, which will
include some magic number and format version, so that's its extensible and
then follow it by lets say little endian structures with 64bit times.
That would mean the size of the file is always some multiple of 4 plus 2,
hence the kernel and utilities can easily find out.

Comments?

Cheers,
Jakub
___________________________________________________________________
Jakub Jelinek | jj@sunsite.mff.cuni.cz | http://sunsite.mff.cuni.cz
Administrator of SunSITE Czech Republic, MFF, Charles University
___________________________________________________________________
UltraLinux | http://ultra.linux.cz/ | http://ultra.penguin.cz/
Linux version 2.2.5 on a sparc64 machine (3958.37 BogoMips)
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