Date: Sun, 14 Dec 2003 16:33:18 -0800 (PST) From: Don Lewis <truckman@FreeBSD.org> To: scottl@FreeBSD.org Cc: mb@imp.ch Subject: Re: HAVE TRACE & DDB Re: FreeBSD 5.2-RC1 released Message-ID: <200312150033.hBF0XIeF066055@gw.catspoiler.org> In-Reply-To: <3FDC887D.9060605@freebsd.org>
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On 14 Dec, Scott Long wrote:
> Don Lewis wrote:
>> Following up to myself ...
>>
>> It looks like we're trying to recycle this vnode because of the
>> following sysinstall code, in distExtractTarball():
>>
>> if (is_base && RunningAsInit && !Fake) {
>> unmounted_dev = 1;
>> unmount("/dev", MNT_FORCE);
>> } else
>> unmounted_dev = 0;
>>
>> I'm guessing that the purpose of this code is to unmount devfs from /dev
>> so that when the base distribution is unpacked it can populate /dev from
>> the tarball. This seems wrong, because it looks like the root file
>> system is mounted on /mnt, and devfs is also mounted on /mnt/dev ...
>>
>> What happens if we forceably umount /dev while /dev/whatever holds a
>> mounted file system? It looks like this is handled by vgonechrl(). It
>> looks to me like vclean() is going to do some scary stuff to this vnode.
>>
>
> As Jeff pointed out, vfs_subr.c rev 1.461 might be the immediate problem
> here. However, I can't believe that umounting devfs while it is in use
> can possibly be the right thing to do. Does devfs have to be mounted in
> the /mnt? Is it a chroot issue?
I think it might have something to do with chroot. In that case we
might need devfs mounted in /mnt/dev in order to mount the installation
media. In that case we are really unmounting /mnt/dev and remounting it
again. In that case, we may not be getting hurt by the file system
mounted on /mnt, but possibly /mnt/usr, since all the file systems
except /mnt are mounted using the devices found in /mnt/dev.
A quick test would be to not partition the disk and install into one
large file system.
I don't know why sysinstall wants to use the /mnt/dev devices for the
destination file systems anyway. It could just use the /dev devices
before it chroots. It would probably still need /mnt/dev for the
installation media, and we may still need to fix vfs_subr.c or whatever.
>> BTW, I think the root vnode is the root of the md file system, not the
>> root of the file system being populated by sysinstall. I don't know why
>> there would be anything to sync at this point, though.
>>
>> I suspect that removing the above sysinstall code will fix the immediate
>> problem, but there is still much I don't understand.
>
> Removing this code will likely result in sysinstall reporting errors to
> the user about not being able to unpack the files into /dev. Or even
> worse, it might succeed and temporarily replace the valid entries with
> invalid ones.
>
> Scott
>
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