This patchset includes the patches to cleanup get_node() I had
sent earlier,  with the Sign-off added. No other changes were
made to those patches since I last sent.

Enable multiple mounts of devpts filesystem so each container can allocate
ptys independently.

User interface:

        Since supporting multiple mounts of devpts can break user-space, this
        feature is enabled only under a new mount option (-o newinstance).

        If this option is never specified, this patchset should not change
        any behavior.  i.e existing single-namespace semantics are preserved
        across any remounts of /dev/pts (as long as none of them use the new
        option).  So old startup scripts should continue to work.

        If the '-o newinstance' option is specified, then a new 'private' mount
        of devpts is created. Ptys in this private instance are independent
        of ptys created in other devpts instances. For this to be fully
        functional, /dev/ptmx must be a bind-mount of '/dev/pts/ptmx'

                mount -t devpts -o newinstance lxcpts /dev/pts
                mount -o bind /dev/pts/ptmx /dev/ptmx

        See [PATCH 11/11] for more details on usage.

Implementation notes:

        1. To enable multiple mounts of /dev/pts, (most) devpts interfaces
           need to know which instance of devpts is being accessed. This
           patchset uses the 'struct inode' or 'struct tty_struct' of the
           device being accessed to identify the appropriate devpts instance.
           Hence the need for the /dev/pts/ptmx bind-mount.

        2. See comments in get_sb_ref() in fs/super.c (could not find
           existing interfaces that accomplish it) Or is there a better
           way ?

        3. Mount options must be parsed twice during mount (once to determine
           the mode of mount (single/multi-instance) and once to actually
           save the options. There does not seem to be an easy way to 
           parse once and reuse (See 'safe_process_mount_opts()' in
           PATCH 11/11)

        [PATCH 1/11]: Move tty lookup/reopen to tty_open
        [PATCH 2/11]: Add an instance parameter to devpts interfaces
        [PATCH 3/11]: Simplify devpts_get_tty()
        [PATCH 4/11]: Simplify devpts_pty_new()
        [PATCH 5/11]: Simplify devpts_pty_kill
        [PATCH 6/11]: Remove devpts_root global
        [PATCH 7/11]: Per-mount allocated_ptys
        [PATCH 8/11]: Per-mount 'config' object
        [PATCH 9/11]: Extract option parsing to new function
        [PATCH 10/11]: Ability to internally create ptmx 
        [PATCH 11/11]: Enable multiple instances of devpts

Changelog [v3]:

        - Port to 2008-08-28 ttydev tree
        - Rename new mount options to 'ptmxmode' and 'newinstance'.
        - [Alan Cox] Use tty driver data to identify devpts (this is used to
          cleanup get_node() in devpts_pty_kill()).
        - [H. Peter Anvin] get_node() cleanup in devpts (which was enabled by
          the inode/tty parameter to devpts interfaces)
        - Bugfix in multi-mount mode (see Patch 11/11).
        - Executed pty tests in LTP (in both single-instance and multi-instance
        - Should be bisect-safe :-)

Changelog [v2]:

        - New mount option '-o newmnt' added (patch 8/8)
        - Support both single-mount and multi-mount semantics (patch 8/8)
        - Automatically create ptmx node when devpts is mounted (patch 7/8)
        - Extract option parsing code to new function (patch 6/8)
        - Make 'config' params per-mount variables (patch 5/8)
        - Slightly re-ordered existing patches in set (patches 1/8, 2/8)

        - Do we need a '-o ptmxuid' and '-o ptmxgid' options as well ?
        - Add a config option to enable multiple-mounts of devpts.
        - (Sometime in future) Remove even initial kernel mount of devpts 
        - Any other good test suites to test this (besides LTP, sshd).
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