[Devel] Re: [ckrm-tech] [PATCH 0/2] resource control file system - aka containers on top of nsproxy!

[Herbert Poetzl]

On Mon, Mar 12, 2007 at 03:00:25AM -0700, Paul Menage wrote:
> On 3/11/07, Paul Jackson <pj at sgi.com> wrote:
> >
> > My current understanding of Paul Menage's container patch is that it is
> > a useful improvement for some of the metered classes - those that could
> > make good use of a file system like hierarchy for their interface.
> > It probably doesn't benefit all metered classes, as they won't all
> > benefit from a file system like hierarchy, or even have a formal name
> > space, and it doesn't seem to benefit the name space implementation,
> > which happily remains flat.
> 
> Well, what I was aiming at was a generic mechanism that can handle
> "namespaces", "metered classes" and other ways of providing
> per-task-group behaviour. So a system-call API doesn't necessarily
> have the right flexibility to implement the possible different kinds
> of subsystems I envisage.
> 
> For example, one way to easily tie groups of processes to different
> network queues is to have a tag associated with a container, allow
> that to propagate to the socket/skbuf priority field, and then use
> standard Linux traffic control to pick the appropriate outgoing queue
> based on the skbuf's tag.
> 
> This isn't really a namespace, and it isn't really a "metered class".
> It's just a way of associating a piece of data (the network tag) with
> a group of processes.
> 
> With a filesystem-based interface, it's easy to have a file as the
> method of reading/writing the tag; with a system call interface, then
> either the interface is sufficiently generic to allow this kind of
> data association (in which case you're sort of implementing a
> filesystem in the system call) or else you have to shoehorn into an
> unrelated API (e.g. if your system call talks about "resource limits"
> you might end up having to specify the network tag as a "maximum
> limit" since there's no other useful configuration data available).
> 
> As another example, I'd like to have a subsystem that shows me all the
> sockets that processes in the container have opened; again, easy to do
> in a filesystem interface, but hard to fit into a
> resource-meteting-centric or namespace-centric system call API.

why? you simply enter that specific space and
use the existing mechanisms (netlink, proc, whatever)
to retrieve the information with _existing_ tools,
no need to do anything unusual via the syscall API

and if you support a 'spectator' context or capability
(which allows to see the _whole_ truth) you can also
get this information for _all_ sockets with existing
tools like netstat or lsof ...

best,
Herbert

> Paul
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