Date: Sun, 4 May 1997 06:31:18 +1000 From: Bruce Evans <bde@zeta.org.au> To: imp@village.org, thorpej@nas.nasa.gov Cc: bde@zeta.org.au, hackers@freebsd.org Subject: Re: Mounting other people's disks? Message-ID: <199705032031.GAA18770@godzilla.zeta.org.au>
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>In message <199705031641.JAA04537@lestat.nas.nasa.gov> Jason Thorpe writes: >: The other port that uses MBR partitions, NetBSD/powerpc, uses the >: "absolute" approach (no "slices" of any sort); if a NetBSD disklabel I think this thread was originally about OpenBSD labels vs FreeBSD label handling and I wrote `NetBSD' instead of `OpenBSD' by mistake. >: is found, its partition information is used, else the information from >: the MBR is used. The MBR and the NetBSD disklabel must be consistent >: for partitions that both OpenFirmware and NetBSD share (such as the >: FAT where the boot program is loaded from). >OpenBSD/arc seems to do exactly the same thing. 'c' is the whole >disk, and there must be an MBR if you wanna use that disk to load the >OS off of. I don't think it's the same. There is no `whole disk' partition in the i386 MBR (or in secondary BRs), so there is no way for a `whole disk' `c' partition to be consistent with the MBR. This is probably why the whole OpenBSD label is rejected. FreeBSD does a consistency check that the 'c' partition is fairly consistent with the slice (it must have the same offset and must not be larger). If the `c' partition starts at absolute offset 0, then there are serious problems locating the label. The label can't always be in absolute sector LABELSECTOR=1 (except when the slice starts at absolute sector 0) since there may be something else there. If the label is in absolute sector (start_of_slice + LABELSECTOR), the everything that deals with labels needs to have machine-dependent code to locate it. The general case, with Disk Manager(s) and extended partitions, is quite complicated. Bruce
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