Quoting Eric W. Biederman (ebiederm@xxxxxxxxxxxx): > Al Viro <viro@xxxxxxxxxxxxxxxxxx> writes: > > > On Mon, Jan 23, 2012 at 04:41:25PM -0800, Linus Torvalds wrote: > > > >> Right. I think the opportunity for problems should be pretty small. > >> > >> And it's not like the pty itself wouldn't continue to work - it's just > >> that programs like /usr/bin/tty wouldn't be able to *find* it. > >> > >> Although who knows - maybe there is some other subtle interaction. > > > > FWIW, the subtle and nasty part in all that is that you can mknod /dev/ptmx > > and it *will* work, refering to the "initial" instance. That's what > > concerns me about the chroot scenarios - > > mknod /jail/dev/ptmx c 5 2 > > mkdir /jail/dev/pts > > mount -t devpts /jail/dev/pts > > chroot /jail > > works fine right now, but with that change behaviour will be all wrong - > > opening /dev/ptmx inside of jail will grab you a pts, all right, but > > it will *not* show up in (jail) /dev/pts/* as it does with the current > > kernel. > > > > Note that if you replace that mknod with symlink pts/ptmx /jail/dev/ptmx > > the things will keep working. However, that will _only_ work for kernels > > with DEVPTS_MULTIPLE_INSTANCES - without it you won't get ptmx inside > > devpts (which is arguably wrong, BTW) > > For testing I would recommend looking at the distro chroot build cases. Do you have a specific example in mind? I would expect build chroots generally don't mount a devpts. > It looks like relatively recent udev still creates /dev/ptmx and does Boy, it does, and it's stubborn about it. Removing the /lib/udev/rules.d entry doesn't stop it. (this is after I've had an init job replace the devtmpfs-created ptmx entry with a symlink) So current distros (well, Ubuntu and Fedora at least) would need to at least (a) fix udev, (b) change the default devpts mount (done from initramfs) to add ptmxmode=666, (c) (if not done in udev) create the /dev/ptmx symlink. For safety I'd recommend creating /dev/pts/ptmx with DEVPTS_MULTIPLE_INSTANCES=n (or dropping that support), and by default setting ptmxmode to 666 as that's what udev does. > not create the symlink. So we might get into the awkward situation of > /dev/ptmx not matching /dev/pts/ptmx with something as simple as > initramfs mounting /dev/pts and then initscripts mounting /dev/pts. That shouldn't matter with a symlink, though it is sloppy. -serge _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
