DEVFS in a chroot?

[M. Warner Losh]

In message: <6695.1083331489 at critter.freebsd.dk>
            "Poul-Henning Kamp" <phk at phk.freebsd.dk> writes:
: In message <20040430.070341.26991317.imp at bsdimp.com>, "M. Warner Losh" writes:
: >In message: <5473.1083327210 at critter.freebsd.dk>
: >            "Poul-Henning Kamp" <phk at phk.freebsd.dk> writes:
: >: >Should I mount /var/chroot/dev as type devfs?
: >: 
: >: Yes:
: >: 
: >: 	mount -t devfs randomargument	/var/chroot/dev
: >
: >What if I have hundreds of these chroots?  We build our product inside
: >a chroot right now and I'm worried what the overhead of
: >mounting/unmounting this for every build would be...
: 
: As far as I recall, our mountlist handling is not optimised for
: hundreds of simultaneous mountpoints: we basically walk the list.
: That said, I belive we only do so during the actual mount/unmount
: operations, so I do not think there is a performance issue as such.

Would the performance issues be mitigated by mounting/unmounting devfs
all the time?  Eg, only mount it while it is actively being used?

Also, the devices that the chroot needs to access are best
characterized as simple: null, random, tty.  It looks like most of the
issues can be delt with, but like you say, there appear to be problems
with things like /dev/tty.  One alternative would be to tar up /dev
and extract it into the chroot.  However, this appears to have
problems with /dev/tty being wrong for users on other ttys.  I've not
yet investigated the problems that might accrue with things like ptys
and people doing a chroot outside of the build system.

Warner