lkml.org 
[lkml]   [2002]   [Jan]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: 2.5.2-pre7 still missing bits of kdev_t
    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.]
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:15    [W:0.024 / U:0.568 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site