RFC : Link with USERCR

Link lxc_checkpoint, lxc_restart with USERCR[2]

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:
- For simplicity, this patchset currently links *statically* with USERCR. We should eventually build checkpoint.o and restart.o in USERCR as shared objects and link lxc_checkpoint/lxc_restart with these shared objects and liblxc.so. (This also required rebuilding lxc-execute statically, so lxc_checkpoint can communicate with lxc-execute to get the root-pid of container).

- Determine if lxc_checkpoint needs a --container option (see TODOs in src/lxc/checkpoint.c)

- This patchset was tested using lxc-macvlan.conf. But for the VNC server testing I ran into a problem with lxc-macvlan.conf. I switched to 'lxc-no-netns.conf' and was able to C/R the VNC server. 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 :-)

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 USERCR

	$ cd /root

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

	$ git-checkout ckpt-v20 

# Apply patches in the following set:

# https://lists.linux-foundation.org/pipermail/containers/2010-March/023793.html

$ cd /root/user-cr

$ make

This should create restart.o and checkpoint.o

2. Build/install lxc_checkpoint and lxc_restart

# Do normal LXC build/install of 0.6.5.

# Then replace 'lxc-execute', 'lxc-checkpoint', 'lxc-restart' with # new version. i.e Apply attached patches and:

$ cd src/lxc

$ USERCR=/root/user-cr \
make -f Makefile2 lxc_checkpoint lxc_restart lxc_execute

$ cp lxc_checkpoint lxc_restart lxc-execute /usr/local/bin

3. Checkpoint/restart a simple LXC container

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

	$ lxc-freeze --name foo

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

	$ lxc-unfreeze --name foo

	$ lxc-stop --name foo

	$ lxc-restart --name foo --image /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-freeze --name foo

etc

[1]: cr-tests: git://git.sr71.net/~hallyn/cr_tests.git
[2]: USERCR: git://git.ncl.cs.columbia.edu/pub/git/user-cr.git