linux-kernel - Re: [Devel] [RFC PATCH 0/4] Container Freezer: Reuse Suspend Freezer

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Date:	Fri, 4 Apr 2008 09:11:06 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Paul Menage <menage@...gle.com>
Cc:	matthltc@...ibm.com,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [Devel] [RFC PATCH 0/4] Container Freezer: Reuse Suspend
	Freezer

Quoting Paul Menage (menage@...gle.com):
> On Thu, Apr 3, 2008 at 2:03 PM,  <matthltc@...ibm.com> wrote:
> >
> >    * "freezer.kill"
> >
> >      writing <n> will send signal number <n> to all tasks
> >
> 
> My first thought (not having looked at the code yet) is that sending a
> signal doesn't really have anything to do with freezing, so it
> shouldn't be in the same subsystem. Maybe a separate subsystem called
> "signal"?
> 
> And more than that, it's not something that requires any particular
> per-process state, so there's no reason that the subsystem that
> provides the "kill" functionality shouldn't be able to be mounted in
> multiple hierarchies.
> 
> How about if I added support for stateless subsystems, that could
> potentially be mounted in multiple hierarchies at once? They wouldn't
> need an entry in the css set, since they have no state.
> 
> >  * 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
> 
> Could we separate this out into two files? One called "freeze" that's
> a 0/1 for whether we're intending to freeze the subsystem, and one
> called "frozen" that indicates whether it is frozen? And maybe a
> "state" file to report the RUNNING/FREEZING/FROZEN distinction in a
> human-readable way?

One thing Oren had mentioned for checkpoint/restart was having more
states - i.e. restoring, checkpointing...  So then (assuming we used
this subsys for that) we'd have more than the two files.  Which is
probably fine, just wanted to point that out.

-serge
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