Re: kern/59783: Can't mount the "special" SGI volume formatted cd9660

["Michael van Elst via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR kern/59783; it has been noted by GNATS.

From: mlelstv%serpens.de@localhost (Michael van Elst)
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/59783: Can't mount the "special" SGI volume formatted cd9660
Date: Sat, 22 Nov 2025 22:13:32 -0000 (UTC)

 gnats-admin%NetBSD.org@localhost ("Izumi Tsutsui via gnats") writes:
 
 > Ah, I see, even on sgimips itself?
 > (Other ports cannot mount sgimips install CD)
 
 The install CD is not an ISO image, but a hacked SGI volume. Other
 ports don't support the SGI volume label, but you can create a
 wedge manually at offset 2MB and then mount it.
 
 On sgimips, the SGI volume label is translated into a fictitious
 BSD label, which reports the ISO9660 partition as "4.2BSD" with
 non-zero fsize/bsize/cpg parameters.
 
 If you try to mount this with cd9660, it ignores the partition type
 and interprets 'fsize' as a bad session offset. It probably works
 with something like:
 
 Index: sys/fs/cd9660/cd9660_vfsops.c
 ===================================================================
 RCS file: /cvsroot/src/sys/fs/cd9660/cd9660_vfsops.c,v
 retrieving revision 1.105
 diff -p -u -r1.105 cd9660_vfsops.c
 --- sys/fs/cd9660/cd9660_vfsops.c       16 Feb 2025 18:38:58 -0000      1.105
 +++ sys/fs/cd9660/cd9660_vfsops.c       22 Nov 2025 08:13:38 -0000
 @@ -419,7 +419,8 @@ iso_mountfs(struct vnode *devvp, struct 
         error = VOP_IOCTL(devvp, DIOCGDINFO, &label, FREAD, FSCRED);
         if (!error) {
                 /* XXX more sanity checks? */
 -               sess = label.d_partitions[DISKPART(dev)].p_cdsession;
 +               if (label.d_partitions[DISKPART(dev)].p_fstype == FS_ISO9660)
 +                       sess = label.d_partitions[DISKPART(dev)].p_cdsession;
         } else {
                 /* fallback to old method */
                 error = VOP_IOCTL(devvp, CDIOREADMSADDR, &sess, 0, FSCRED);