linux-kernel - Re: Notifying on empty cgroup

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Message-Id: <409331389795100@web18j.yandex.ru>
Date:	Wed, 15 Jan 2014 16:11:40 +0200
From:	Victor Porton <porton@...od.ru>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	cgroups mailinglist <cgroups@...r.kernel.org>
Subject: Re: Notifying on empty cgroup

15.01.2014, 15:59, "Michal Hocko" <mhocko@...e.cz>:
> [CCing cgroups mailing list]
> On Wed 15-01-14 06:12:45, Victor Porton wrote:
>
>>  I want to write software which needs to receive a signal when the cgroup
>>  created by it becomes empty. (After this the empty cgroup should be deleted
>>  just not to clutter the memory.)
>>
>>  If the kernel does not support such notifications, it should be improved.
>>  This functionality is crucial for some kinds of software.
>>
>>  There is /sys/fs/cgroup/systemd/release_agent but I don't understand how to
>>  use it. I don't understand why we would need it at all.
>
> "1.4 What does notify_on_release do ?" in
> Documentation/cgroups/cgroups.txt the kernel source doesn't help?

I've read it. I understand what it does. I don't understand how to use it in practice nor why it is done this way.

>>  Starting a binary on emptying a cgroup with the purpose to notify an other
>>  binary looks like a big overkill.
>
> the binary can do rmdir which is what you want, no?

I suppose a base package should do that, not my specific software. Do I understand right?

>>  Also my program should work in userspace without the need to use
>>  release_agent which can be accessed only by root.
>
> The release_agent is global for all groups so the program doesn't have
> to care.

Again: What MY program should do?

>>  Note that my work is related with sandboxing software (running a program in
>>  closed environment, so that it would be unable for example to remove user's
>>  files).
>>
>>  See also
>>  http://portonsoft.wordpress.com/2014/01/11/toward-robust-linux-sandbox/
>>
>>  --
>>  Victor Porton - http://portonvictor.org
>>  --
>>  To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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>
> --
> Michal Hocko
> SUSE Labs

-- 
Victor Porton - http://portonvictor.org
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