Date: Sat, 03 Feb 2001 09:48:56 -0800 From: Peter Wemm <peter@netplex.com.au> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: Warner Losh <imp@harmony.village.org>, Jordan Hubbard <jkh@winston.osd.bsdi.com>, John Indra <john@naver.co.id>, freebsd-current@FreeBSD.ORG Subject: Re: DEVFS newbie... Message-ID: <200102031748.f13HmuW44694@mobile.wemm.org> In-Reply-To: <14457.981221808@critter>
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Poul-Henning Kamp wrote:
> In message <200102031729.f13HTL960996@harmony.village.org>, Warner Losh write
s:
> >In message <82167.981191888@winston.osd.bsdi.com> Jordan Hubbard writes:
> >: Couldn't you also do "mount -t devfs -o nonewdev devfs /home/jail/dev"
> >: and then cd /home/jail/dev ; rm $devices_i_dont_want_in_my_jails ? It
> >: seems that "read my lips: no new devices" should be an option you can
> >: set from the very initial mount so that people can't also figure out
> >: how to get root, remove a /dev entry and replace it with one of their
> >: own. Come to think of it, there should also be a -o staticdev option
> >: to disallow *any* changes after the initial mount. That would make
> >: some of our more paranoid sysadmins happy.
> >
> >My concern is that I usually know what devices I want (/dev/null,
> >/dev/zero, /dev/tty). That makes it harder to delete all of them not
> >on the list.
>
> I have seriously been thinking about some way to say something like
> mount -t devfs -o jailset /home/jail/dev
> but an elegant implementation evades me at this moment.
As bizzare as it sounds, I like Julian's hack for populating this stuff...
ie: use a hard link to propagate nodes to the jailed /dev.
eg: mount -t devfs -o empty /home/jail/dev
ln /dev/null /home/jail/dev/null
ln /dev/zero /home/jail/dev/zero
...
mount -u -o ro /home/jail/dev
It solves several problems, but is kinda odd as it involves a
cross-filesystem hard link. This is another way oround the "oops, I didn't
mean to rm /dev/null" - ie:
mount -t devfs /mnt
ln /mnt/null /dev
umount /mnt
The VOP_LINK() stuff has access to the source and destination, so it doesn't
have to guess what do do on incomplete information (eg: fake major number).
On the other hand... Suppose whiteouts were implemented...
mount -t devfs -o empty /home/jail/dev
cd /home/jail/dev
rm -W null zero log ....
mount -u -o ro /home/jail/dev
ie: start with the initial state as "whiteouts on everything" and then
selectively remove the whiteout for things you actually want... Then freeze
it by flipping on the readonly bit.
> And again, it hinges on an extensible set of mount options.
Yeah. Maybe pass in arbitary strins "empty" instead of trying to convert
everything to a flag bit? I've been bothered about this for a while.
Cheers,
-Peter
--
Peter Wemm - peter@FreeBSD.org; peter@yahoo-inc.com; peter@netplex.com.au
"All of this is for nothing if we don't go to the stars" - JMS/B5
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