Link LXC with USERCR

Resending patches after fixing whitespace damage and the typo in configure.ac. Add a section to patch-0 (below) to describe the kernel build (commit-id, config tokens etc).

---
Following set of patches, when applied to LXC 0.6.5 and built with usercr, enable lxc_checkpoint and lxc_restart of some simple containers.

TODO:
- Determine if lxc_checkpoint needs a --container option (see TODOs in src/lxc/checkpoint.c)
- This patchset was tested using lxc-nonetns.conf. I ran into a problem creating a bridge with lxc-veth.conf and lxc-macvlan.conf. I have not debugged the problem with VNC and lxc-macvlan.conf.
- 'global_send_sigint' is still a global variable in USERCR. We need to define a better interface to expose its functionality to callers of app_restart().
- Choose better names and API for USERCR :-)
- Additional TODOs specific to checkpoint/restart are listed in their specific patches.

Changelog[v3]:
- Renamed --image option to --statefile
- Added --with-libcr configuration option to specify the path to usercr (see usage below).
- lxc-checkpoint now implicitly freezes before and unfreezes after checkpoint.
- Implemented the --pause options to lxc-checkpoint and lxc-restart and the --kill option to lxc-checkpoint.
- Ported to ckpt-v20-dev (required adding CHECKPOINT_NONETNS flag to app_checkpoint() to work around)

Changelog[v2]:

(Based on feedback from Oren Laadan, Serge Hallyn, Daniel Lezcano and Cedric Le Goater)

- Rather than drop --directory option to lxc_checkpoint/lxc_restart add a new option (--image).
- Integrate lxc_checkpoint to work with USERCR
- USERCR renamed usercr.h to "app-checkpoint.h"
- USERCR does not create/install libcheckpoint.a and usercr.h for now. So link directly with app-checkpoint.h, restart.o and checkpoint.o
- USERCR renames the interfaces to app_checkpoint() and app_restart() 'struct app_checkpoint_args' 'struct app_restart_args'.

USAGE:

1. Build C/R-enabled Linux kernel

	$ cd /root

	$ git-clone  git://www.linux-cr.org/pub/git/linux-cr.git linux-cr

	$ cd linux-cr

	$ git-checkout ckpt-v20-dev

I tested with commit 3522c57a9ec6f08a129a78322318abcb4467db28 as HEAD.

# Ensure following tokens are set in .config

CONFIG_CHECKPOINT_SUPPORT=y
CONFIG_SYSVIPC_CHECKPOINT=y
CONFIG_CHECKPOINT=y
CONFIG_CHECKPOINT_NETNS=y
CONFIG_CHECKPOINT_DEBUG=y

CONFIG_CGROUPS=y
CONFIG_CGROUP_FREEZER=y
CONFIG_NAMESPACES=y
CONFIG_CGROUP_NS=y
CONFIG_UTS_NS=y

CONFIG_IPC_NS=y
CONFIG_USER_NS=y
CONFIG_PID_NS=y
CONFIG_NET_NS=y

# Build, install, reboot on new kernel

# After every reboot, ensure '-o newinstance' mount option to /dev/pts
works (see Documentation/filesystems/devpts.txt for details). In short, run following commands on each reboot:

$ rm /dev/ptmx

$ ln -s pts/ptmx /dev/ptmx

$ chmod 666 /dev/pts/ptmx

1. Build USERCR

	$ cd /root

	$ git-clone git://git.ncl.cs.columbia.edu/pub/git/user-cr.git user-cr

	$ cd user-cr

	$ git-checkout ckpt-v20-dev

Tested with commit e275f77e4a82d228c1df14dbeb691342e32cdac2 as HEAD.

# Apply following two patches:

https://lists.linux-foundation.org/pipermail/containers/2010-March/024037.html
https://lists.linux-foundation.org/pipermail/containers/2010-March/024038.html

$ KERNELSRC=/root/linux-cr make

Build USERCR by pointing to corresponding kernel-source. This should create restart.o and checkpoint.o needed by LXC.

I did not need to, but you may need to compile checkpoint.o and restart.o with -fPIC compiler option.

$ make install

2. Build/install LXC

	$ cd /root

	$ git-clone git://lxc.git.sourceforge.net/gitroot/lxc/lxc lxc.git

	$ cd lxc.git

# Apply attached patches to LXC (I tested with these patches applied to commit 9ea8066aa67b808f71f46e346bd7a215e2a355f3)

$ autogen.sh

$ ./configure --with-libcr=/root/user-cr

This will fail if /root/user-cr does not container checkpoint.o, restart.o and app-checkpoint.h files
$ make

$ make install

3. Checkpoint/restart a simple LXC container

	$ lxc-execute --name foo --rcfile lxc-no-netns.conf -- /bin/sleep 1000

	$ lxc-checkpoint --name foo --statefile /root/lxc-foo.ckpt

	$ lxc-stop --name foo

	$ lxc-restart --name foo --statefile /root/lxc-foo.ckpt

4. Checkpoint/restart other LXC containers such as:

- a file-io session (see run-fileio1 in cr-tests[1])

- process-tree (see run-ptree1 in cr-tests[1])

- A vi session inside a VNC Server using "twm". i.e

$ cat /root/.vnc/xstartup
#!/bin/sh

xsetroot -solid grey
vncconfig -iconic &
xterm -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" & twm &

$ lxc-execute --name foo --rcfile lxc-no-netns.conf -- \
/usr/bin/vncserver :1

$ vncviewer :1

# Open a vi session

$ lxc-checkpoint --name foo --statefile /root/vnc.ckpt

$ lxc-stop --name foo

$ lxc-restart --pause --name foo --statefile /root/vnc.ckpt

# Leaves the server frozen due to --pause

$ lxc-unfreeze --name foo

$ vncviewer :1

# Should bring up the old VNC session with vi window

[1]: cr-tests: git://git.sr71.net/~hallyn/cr_tests.git