Messages in this thread | | | From | Andries.Brouwer@cwi ... | Date | Fri, 4 Jan 2002 01:47:52 GMT | Subject | Re: 2.5.2-pre7 still missing bits of kdev_t |
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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/
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