This patchset is a prototype using the container infrastructure and
the swsusp freezer to freeze a group of tasks.

2 files are defined by the freezer subsystem in the container
filesystem :

   * "freezer.freeze"

     writing 1 will freeze all tasks and 0 unfreeze
     reading will return the status of the freezer
 
   * "freezer.kill"

     writing <n> will send signal number <n> to all tasks

* Usage :

   # mkdir /containers/freezer
   # mount -t container -ofreezer freezer  /containers/freezer
   # mkdir /containers/freezer/0
   # echo $some_pid > /containers/freezer/0/tasks

to get status of the freezer subsystem :

   # cat /containers/freezer/0/freezer.freeze
   RUNNING

to freeze all tasks in the container :

   # echo 1 > /containers/freezer/0/freezer.freeze
   # cat /containers/freezer/0/freezer.freeze
   FREEZING
   # cat /containers/freezer/0/freezer.freeze
   FROZEN

to unfreeze all tasks in the container :

   # echo 1 > /containers/freezer/0/freezer.freeze
   # cat /containers/freezer/0/freezer.freeze
   RUNNING

to kill all tasks in the container :

   # echo 9 > /containers/freezer/0/freezer.kill

* Caveats: 

  - the FROZEN status is calculated and changed when the container
    file "freezer.freeze" is read.
  - frozen containers will be unfreeze when a system is resumed after 
    a suspend. This is addressed by the last patch.

* Series

  The first patches make the freezer available to all architectures
  before implementing the freezer subsystem.

  - add the TIF_FREEZE flag to all archs
  - make refrigerator() available to all archs
  - implement freezer subsystem 
  - do not unfreeze a frozen container when the system is resumed 

Comments are welcome.

Thanks,

C.
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