Messages in this thread | | | Date | Wed, 9 Apr 2008 20:59:55 -0500 | From | "Serge E. Hallyn" <> | Subject | Re: [RFC][PATCH 0/7] Clone PTS namespace |
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Quoting Eric W. Biederman (ebiederm@xmission.com): > On Tue, 2008-04-08 at 17:53 -0700, H. Peter Anvin wrote: > > sukadev@us.ibm.com wrote: > > > Devpts namespace patchset > > > > > > In continuation of the implementation of containers in mainline, we need to > > > support multiple PTY namespaces so that the PTY index (ie the tty names) in > > > one container is independent of the PTY indices of other containers. For > > > instance this would allow each container to have a '/dev/pts/0' PTY and > > > refer to different terminals. > > > > > > > Why do we "need" this? There isn't a fundamental need for this to be a > > dense numberspace (in fact, there are substantial reasons why it's a bad > > idea; the only reason the namespace is dense at the moment is because of > > the hideously bad handing of utmp in glibc.) Other than indicies, this > > seems to be a more special case of device isolation across namespaces, > > would that be a more useful problem to solve across the board? > > In short application migration. When you move a running applicaiton > from one machine to another you want to be able to keep the same pseudo > devices. > > The isolation that you have noticed is also an important application and > like the rest of the namespaces if we can solve the duplicate identifier > problem needed to restore checkpoints we also largely solve the > isolation problem. > > This problem is much larger then ptys. ptys are the really in your face > aspect of it. There are a more pseudo devices in the kernel and it is > the device number to device mapping that we are abstracting. So this > really should be done as a device namespace not a pty namespace. > > I would be happy if the first version of the device namespace could not > map anything but pty's (assuming an incremental implementation path). I > really don't think we should do a special case for each kind of device.
Sounds like we're all agreed on this and just doing s/CLONE_NEWPTS/CLONE_NEWDEV/ on the current patchset suffices for now. But,
> Oh and just skimming the patch summary I'm pretty certain this > implementation breaks /sys/class/tty/ptyXX/uevent. Which is another > reason why it would be good to have a single device namespace. So we > only to capture one more namespace and figure out how to deal with it > when mounting sysfs.
Feh, so of course sysfs would have the most interactions for a device namespace, but now we have pty, network, and user namespace all needing some sort of sysfs solution. For a quickfix for CONFIG_USER_SCHED+CONFIG_USER_NS, I just moved /sys/kernel/uids/<uid> to /sys/kernel/uids/<userns_address>/<uid>. But what would be a *good* general solution?
ln -s /sys /proc/self/sys?
-serge
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