Re: [PATCH] kdevt-diff

["H. Peter Anvin" <hpa@zytor.com>]

Andries Brouwer wrote:
> On Wed, Apr 16, 2003 at 09:48:16AM -0700, H. Peter Anvin wrote:
> 
> 
>>Not really, but it's certainly a nice capability.  However, iso9660
>>(RockRidge, actually) has 64 bits of dev_t space; it's actually split
>>into two 32-bit entries specified as "high 32 bits" and "low 32 bits."
>>
>>I'm not positive if Linux expects those to contain major:minor or
>>0:<16-bit-dev_t>.
> 
>       case SIG('P','N'):
>         { int high, low;
>           high = isonum_733(rr->u.PN.dev_high);
>           low = isonum_733(rr->u.PN.dev_low);
>           /*
>            * The Rock Ridge standard specifies that if sizeof(dev_t) <= 4,
>            * then the high field is unused, and the device number is completely
>            * stored in the low field.  Some writers may ignore this subtlety,
>            * and as a result we test to see if the entire device number is
>            * stored in the low field, and use that.
>            */
>           if((low & ~0xff) && high == 0) {
>             inode->i_rdev = mk_kdev(low >> 8, low & 0xff);
>           } else {
>             inode->i_rdev = mk_kdev(high, low);
>           }
>         }
>         break;
> 
> (Here isonum_733 gets 32 bits.)

OK, in other words, it accepts either format, either:

0x000000000000MMmm or 0x000000MM000000mm

This is perfectly consistent with what dev_t does for a 32:32 split; the
previous form would be the "backwards compatibility" format and the
second the "new" format.

	-hpa