From jgarzik@mandrakesoft.com Fri Jan 4 01:13:34 2002
reiserfs is blindly storing the kernel's kdev_t value raw to disk.
AFAICS this will need a policy decision not just cleanup, before it
works in 2.5.2 properly. If we switch the kernel to 12:20 major:minor
numbers, suddenly the reiserfs disk format changes based on kernel
version, and earlier kernels see corrupted major:minor numbers.
No, not really. For how to do this, see a fragment of example code
that Linus removed from kdev_t.h in pre6, it went something like
(adapted for 12+20 instead of 16+16):
int major(dev_t dev) {
int ma;
ma = (dev >> 20);
if (!ma)
ma = (dev >> 8);
return ma;
}
int minor(dev_t dev) {
if (dev >> 20)
return (dev & 0xfffff);
else
return (dev & 0xff);
}
dev_t mkdev(int ma, int mi) {
if (mi & ~0xff)
return ((ma << 20) + mi);
else
return ((ma << 8) + mi);
}
(with the correctness conditions that ma is 12-bit,
mi is 20-bit, and major 0 has only 8-bit minors).
You see that the representation of old values does not change.
No disk corruption.
Andries
[I didnt spell it out, but you understand: the dev_t is the on-disk
format, the conversion finds the major and minor, and these are
combined again into a kdev_t for use by the kernel]
[Similar code occurs is isofs/rock.c, where a 64-bit dev
must be converted.]
[I don't know whether reiserfs is a Linux-only filesystem.
If it is not, and has a disk format that is OS-independent,
a third struct stat_data might be needed, since the 12+20
is not universal, so 32+32 would be the better choice.]
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This archive was generated by hypermail 2b29 : Mon Jan 07 2002 - 21:00:23 EST