Re: Re: [RFC] How to handle the rules engine for cgroups

[kamezawa . hiroyu]

----- Original Message -----
>On Fri, Jul 11, 2008 at 09:55:01AM +0900, KAMEZAWA Hiroyuki wrote:
>> On Thu, 10 Jul 2008 11:40:35 -0400
>> Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
>> 
>> > On Thu, Jul 10, 2008 at 10:48:52AM -0400, Rik van Riel wrote:
>> > > On Thu, 10 Jul 2008 02:23:52 -0700
>> > > "Paul Menage" <menage@xxxxxxxxxx> wrote:
>> > > 
>> > > > I don't see the rule-based approach being all that useful for our nee
ds.
>> > > 
>> > > Agreed, there really is no need for a rule-based approach in kernel spa
ce.
>> > > 
>> > > There are basically three different cases:
>> > > 
>> > > 1) daemons get started up in their own process groups, this can
>> > >    be handled by the initscripts
>> > > 
>> > > 2) user sessions (ssh, etc) start in their own process groups,
>> > >    this can be handled by PAM
>> > > 
>> > > 3) users fork processes that should go into special process
>> > >    groups - this could be handled by having a small ruleset
>> > >    in userspace handle things, right before calling exec(),
>> > 
>> > That means application launcher (ex, shell) is aware of the right cgroup
>> > targeted application should go in and then move forked pid to right
>> > cgroup and call exec? Or you had something else in mind?
>> >  
>> > >    it can even be hidden from the application by hooking into
>> > >    the exec() call
>> > > 
>> > 
>> > This means hooking into libc. So libc will parse rules file, determine
>> > the right cgroup, place application there and then call exec?
>> > 
>> 
>> Hmm, as I wrote, the rule that the child inherits its own parent't is very
>> strong rule. (Most of case can be handle by this.) So, what I think of is
>> 
>> 1. support a new command (in libcg.)
>>   - /bin/change_group_exec ..... read to /etc/cgroup/config and move cgroup
>>                                  and call exec.
>> 2. and libc function
>>   - if necessary.
>> 
>> 1. is enough because admin/user can write a wrapper script for their
>> applications if "child inherits parent's" isn't suitable.
>> 
>> no ?
>> 
>
>If admin has decided to group applications and has written the rules for
>it then applications should not know anything about grouping. So I think
>application writing an script for being placed into the right group should
>be out of question. Now how does an admin write a wrapper around existing
>application without breaking anything else.
>
Sure.

>One thing could be creating soft links where admin created alias points
>to wrapper and wrapper inturn invokes the executable. But this will not
>solve the problem if some user decides to invoke the application
>executable directly and not use admin created alias. 
>
yes. It's a hole.

>Did you have something else in mind when it came to creating wrappers
>around applications?
>

I have no strong idea around this but now it seems

 - handling complicated rules under the kernel will got amount of Nacks.
   (and it seems to add some latency.)
 - We cannot avoid the problem discussed here if we handle the rule in 
   userland daemon/process-event-connector.

So, I wonder adding some limitation may make things simple.

  - application under wrapper will be executed under a group defined by admin.
  - application without wrapper will be executed under a group where exec()
    called.

A point is that application-without-wrapper is also under Admin's control beca
use it's executed under a group which calls exec.

But this is not strict control..this is very loose ;)

Thanks,
-Kame

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