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Matt Helsley dc52ddc0e6 container freezer: implement freezer cgroup subsystem 
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: Cedric Le Goater <clg@fr.ibm.com>
Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
Acked-by: Serge E. Hallyn <serue@us.ibm.com>
Tested-by: Matt Helsley <matthltc@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-10-20 08:52:34 -07:00
..
alpha container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
arm container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
avr32 container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
blackfin container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
cris container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
frv container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
h8300 container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
ia64 container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
m32r container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
m68k container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
m68knommu container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
mips container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
mn10300 container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
parisc container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
powerpc container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
s390 container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
sh container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
sparc container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
sparc64 container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
um container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
x86 container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
xtensa container freezer: implement freezer cgroup subsystem 2008-10-20 08:52:34 -07:00
.gitignore arch: Ignore arch/i386 and arch/x86_64 2008-01-19 21:29:39 -08:00
Kconfig Kconfig: eliminate "def_bool n" constructs 2008-10-16 11:21:31 -07:00