Date: Sat, 03 May 1997 19:51:41 -0600 From: Warner Losh <imp@village.org> To: Bruce Evans <bde@zeta.org.au> Cc: thorpej@nas.nasa.gov, hackers@freebsd.org Subject: Re: Mounting other people's disks? Message-ID: <E0wNqSk-0000kN-00@rover.village.org> In-Reply-To: Your message of "Sun, 04 May 1997 06:31:18 %2B1000." <199705032031.GAA18770@godzilla.zeta.org.au> References: <199705032031.GAA18770@godzilla.zeta.org.au>
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In message <199705032031.GAA18770@godzilla.zeta.org.au> Bruce Evans writes: : 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). Umm, the OpenBSD/arc port basically ignores the MBR. It is interesting, yes, but not very interesting to it. All of the disk splitting up is done with respect to the disk label. Many disks have overlapping MBR partitions to deal with the FAT file systems. : 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. While this is a desirable goal, I don't think that OpenBSD/arc can change. There are too many legacy systems to make it worth while. This is basically the "bogus MBR" problem that FreeBSD has had in the past. The MBR is just there for the bios to load the boot loader. Once the boot loader was loaded, it didn't matter any more. The rules in place for FreeBSD are good ones. However, I want and need a way to short circuit them from time to time. So far the best approach that I've been able to come up with is to have the OpenBSD slice take up the entire disk if I need to make it work on FreeBSD at any point in the future. Warner
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