1. 20 Oct, 2008 1 commit
    • Matt Helsley's avatar
      container freezer: implement freezer cgroup subsystem · dc52ddc0
      Matt Helsley authored
      This patch implements a new freezer subsystem in the control groups
      framework.  It provides a way to stop and resume execution of all tasks in
      a cgroup by writing in the cgroup filesystem.
      
      The freezer subsystem in the container filesystem defines a file named
      freezer.state.  Writing "FROZEN" to the state file will freeze all tasks
      in the cgroup.  Subsequently writing "RUNNING" will unfreeze the tasks in
      the cgroup.  Reading will return the current state.
      
      * Examples of usage :
      
         # mkdir /containers/freezer
         # mount -t cgroup -ofreezer freezer  /containers
         # mkdir /containers/0
         # echo $some_pid > /containers/0/tasks
      
      to get status of the freezer subsystem :
      
         # cat /containers/0/freezer.state
         RUNNING
      
      to freeze all tasks in the container :
      
         # echo FROZEN > /containers/0/freezer.state
         # cat /containers/0/freezer.state
         FREEZING
         # cat /containers/0/freezer.state
         FROZEN
      
      to unfreeze all tasks in the container :
      
         # echo RUNNING > /containers/0/freezer.state
         # cat /containers/0/freezer.state
         RUNNING
      
      This is the basic mechanism which should do the right thing for user space
      task in a simple scenario.
      
      It's important to note that freezing can be incomplete.  In that case we
      return EBUSY.  This means that some tasks in the cgroup are busy doing
      something that prevents us from completely freezing the cgroup at this
      time.  After EBUSY, the cgroup will remain partially frozen -- reflected
      by freezer.state reporting "FREEZING" when read.  The state will remain
      "FREEZING" until one of these things happens:
      
      	1) Userspace cancels the freezing operation by writing "RUNNING" to
      		the freezer.state file
      	2) Userspace retries the freezing operation by writing "FROZEN" to
      		the freezer.state file (writing "FREEZING" is not legal
      		and returns EIO)
      	3) The tasks that blocked the cgroup from entering the "FROZEN"
      		state disappear from the cgroup's set of tasks.
      
      [akpm@linux-foundation.org: coding-style fixes]
      [akpm@linux-foundation.org: export thaw_process]
      Signed-off-by: default avatarCedric Le Goater <clg@fr.ibm.com>
      Signed-off-by: default avatarMatt Helsley <matthltc@us.ibm.com>
      Acked-by: default avatarSerge E. Hallyn <serue@us.ibm.com>
      Tested-by: default avatarMatt Helsley <matthltc@us.ibm.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      dc52ddc0