lxclock: Replace named sempahore with flock

The problem: if a task is killed while holding a posix semaphore,
there appears to be no way to have the semaphore be reliably
autmoatically released.  The only trick which seemed promising
is to store the pid of the lock holder in some file and have
later lock seekers check whether that task has died.

Instead of going down that route, this patch switches from a
named posix semaphore to flock.  The advantage is that when
the task is killed, its fds are closed and locks are automatically
released.

The disadvantage of flock is that we can't rely on it to exclude
threads.  Therefore c->slock must now always be wrapped inside
c->privlock.

This patch survived basic testing with the lxcapi_create patchset,
where now killing lxc-create while it was holding the lock did
not lock up future api commands.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
locking: update per Dwight's comment

Create three pairs of functions:
	int process_lock(void);
	void process_unlock(void);
	int container_mem_lock(struct lxc_container *c)
	void container_mem_unlock(struct lxc_container *c)
	int container_disk_lock(struct lxc_container *c);
	void container_disk_unlock(struct lxc_container *c);

and use those in lxccontainer.c

process_lock() is to protect the process state among multiple threads.
container_mem_lock() is to protect a struct container among multiple
threads.  container_disk_lock is to protect a container on disk.

Also remove the lock in lxcapi_init_pid() as Dwight suggested.

Fix a typo (s/container/contain) spotted by Dwight.

More locking fixes are needed, but let's first the the fundamentals
right.  How close does this get us?

Changelog: v2:
	fix lxclock compile

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Dwight Engen <dwight.engen@oracle.com>
lxc-stop: use api, remove lxc_shutdown, extend lxc-stop functionality

implement c->reboot(c) in the api.

Also if the container is not running, return -2.  Currently
lxc-stop will return 0, so you cannot tell the difference
between successfull stopping and noop.

Per stgraber's email:

 - Remove lxc-shutdown
 - Change lxc-stop so that:
   * Default behaviour is to call shutdown(), wait 15s for STOPPED, if
not STOPPED, print a message to the user and call stop() [ NOTE:
actually 60 seconds per followup thread]
   * We have a -r option to reboot the container (with proper check that
the container indeed rebooted within the next 15s)
   * We have a -s option to shutdown the container without the automatic
fallback to stop()
   * Add a -k option allowing a user to just kill a container
(equivalent to old lxc-stop, no shutdown() call and no delay).

and update manpages.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
destroy: implement in the api

This requires implementing bdev->ops->destroy() for each of the backing
store types.  Then implementing lxcapi_clone(), writing lxc_destroy.c
using the api, and removing the lxc-destroy.in script.

(this also has a few other cleanups, like marking some functions
static)

Changelog:
	fold into destroy: fix zfs destroy
	destroy: use correct program name in help

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Move container creation fully into the api

1. implement bdev->create:

python and lua: send NULL for bdevtype and bdevspecs.
They'll want to be updated to pass those in in a way that makes
sense, but I can't think about that right now.

2. templates: pass --rootfs

If the container is backed by a device which must be mounted (i.e.
lvm) then pass the actual rootfs mount destination to the
templates.

Note that the lxc.rootfs can be a mounted block device.  The template
should actually be installing the rootfs under the path where the
lxc.rootfs is *mounted*.

Still, some people like to run templates by hand and assume purely
directory backed containers, so continue to support that use case
(i.e. if no --rootfs is listed).

Make sure the templates don't re-write lxc.rootfs if it is
already in the config.  (Most were already checking for that)

3. Replace lxc-create script with lxc_create.c program.

Changelog:
May 24: when creating a container, create $lxcpath/$name/partial,
and flock it.  When done, close that file and unlink it.  In
lxc_container_new() and lxcapi_start(), check for this file.  If
it is locked, create is ongoing.  If it exists but is not locked,
create() was killed - remove the container.

May 24: dont disk-lock during lxcapi_create.  The partial lock
is sufficient.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>