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    SubjectRe: [RFC][PATCH 0/7] Clone PTS namespace
    Quoting Eric W. Biederman (
    > On Tue, 2008-04-08 at 17:53 -0700, H. Peter Anvin wrote:
    > > 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.

    > 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?


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