From: Tejun Heo <tj@kernel.org>
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Cgroups <cgroups@vger.kernel.org>,
Lennart Poettering <mzxreary@0pointer.de>,
Kay Sievers <kay.sievers@vrfy.org>
Subject: Re: [PATCH 2/2] cgroup: add xattr support
Date: Tue, 17 Jan 2012 09:53:22 -0800 [thread overview]
Message-ID: <20120117175322.GC6762@google.com> (raw)
In-Reply-To: <4F13DAA9.4070703@cn.fujitsu.com>
Hello,
On Mon, Jan 16, 2012 at 04:07:05PM +0800, Li Zefan wrote:
> This is one of the items in the plumber's wish list.
>
> For use cases:
>
> >> What would the use case be for this?
> >
> > Attaching meta information to services, in an easily discoverable
> > way. For example, in systemd we create one cgroup for each service, and
> > could then store data like the main pid of the specific service as an
> > xattr on the cgroup itself. That way we'd have almost all service state
> > in the cgroupfs, which would make it possible to terminate systemd and
> > later restart it without losing any state information. But there's more:
> > for example, some very peculiar services cannot be terminated on
> > shutdown (i.e. fakeraid DM stuff) and it would be really nice if the
> > services in question could just mark that on their cgroup, by setting an
> > xattr. On the more desktopy side of things there are other
> > possibilities: for example there are plans defining what an application
> > is along the lines of a cgroup (i.e. an app being a collection of
> > processes). With xattrs one could then attach an icon or human readable
> > program name on the cgroup.
> >
> > The key idea is that this would allow attaching runtime meta information
> > to cgroups and everything they model (services, apps, vms), that doesn't
> > need any complex userspace infrastructure, has good access control
> > (i.e. because the file system enforces that anyway, and there's the
> > "trusted." xattr namespace), notifications (inotify), and can easily be
> > shared among applications.
> >
> > Lennart
>
> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Ummm... I don't feel too good about this. Why can't those extra
information be kept somewhere else? Overloading cgroupfs as storage
for essentially opaque userland information doesn't seem like a good
idea to me.
Thanks.
--
tejun
next prev parent reply other threads:[~2012-01-17 17:53 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-16 8:06 [PATCH 1/2] cgroup: revise how we re-populate root directory Li Zefan
2012-01-16 8:07 ` [PATCH 2/2] cgroup: add xattr support Li Zefan
2012-01-17 17:53 ` Tejun Heo [this message]
2012-01-18 8:27 ` Li Zefan
2012-01-18 17:47 ` Tejun Heo
2012-01-19 1:49 ` Lennart Poettering
2012-01-18 21:28 ` Kay Sievers
2012-01-18 21:36 ` Tejun Heo
2012-01-19 1:47 ` Lennart Poettering
2012-01-19 2:20 ` Tejun Heo
2012-01-19 2:40 ` Tejun Heo
2012-01-21 3:02 ` Lennart Poettering
2012-01-21 4:00 ` Hugh Dickins
2012-01-21 2:59 ` Lennart Poettering
2012-01-18 7:23 ` [PATCH 1/2] cgroup: revise how we re-populate root directory Sha
2012-01-18 7:59 ` Li Zefan
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