Date: Sat, 21 Jul 2001 19:31:01 -0700 (PDT) From: Ed Alley <alley1@llnl.gov> To: Mike Meyer <mwm@mired.org> Cc: <wea@llnl.gov>, <freebsd-questions@freebsd.org> Subject: Re: Why panic when mounting bad CD? Message-ID: <20010721191608.U4095-100000@jordan.llnl.gov> In-Reply-To: <15193.48484.879754.875650@guru.mired.org>
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So fixating a disk is the same as writing and/or validating the file system descriptor tables for the ISO filesystem on the CD. I see the problem. Thanks for the explanation Mike, I learned alot; if I knew anything about ISO9660 I would try to figure something out myself. :( Ed On Sat, 21 Jul 2001, Mike Meyer wrote: > Ed Alley <alley1@llnl.gov> types: > > I am running FreeBSD 4.3 with an HP 9500 ide CD-RW. > > > > My question is why does the kernel panic > > under these conditions? Does it get lost > > trying to find the disklabel or does the > > kernel think that the numbers it picked > > up are the disklabel and merrily goes > > off into some other world looking for > > the superblock? > > CD's generally use the ISO 9660 file system, not UFS. They don't have > superblocks or disklabels, they have volume descriptors. And yes, if a > file system has bogus description data in it, the system tends to > crash while trying to deal with it. This is true for most file > systems. > > > Wouldn't it be a good idea to have a > > magic number in with the disklabel > > that the kernel could test against > > before it believes what it finds? > > UFS has a magic number in the superblock, and it's checked. ISO 9660 > file systems also have a magic number in the volume descriptor, and > that's checked. The code in -stable check for either the ISO 9660 or > the ISO SIERRA magic numbers, as it understands both formats. > > Neither of these guarantee that the file system descriptor tables are > actually correct. Mounting a file system with a valid magic number and > bogus descriptor tables is generally a bad idea. It appears that an > unfixated CD meets that description. There may be a way to detect that > the CD is unfixated; if so, submitting a patch to the > /usr/src/sys/isofs/cd9660_vfsops.c via a PR would be appreciated. > > <mike > -- > Mike Meyer <mwm@mired.org> http://www.mired.org/home/mwm/ > Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information. > > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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