[pulseaudio-discuss] rtkit: add pid as argument

[Lennart Poettering]

On Sat, 24.04.10 01:18, Maarten Lankhorst (m.b.lankhorst at gmail.com) wrote:

> I'm not sure if I have the right mailing list, since there doesn't
> appear to be a a mailing list for rtkit.
> 
> This is a patch that would allow you to set the realtime priority
> for another process then the one calling rtkit over dbus. This can
> be useful for a 'setsched' like utility, or for wine. Extra
> validation on the given pid isn't needed, since verify_process_user
> will do this anyhow.

Hmm, while I am not strictly against this I don't really see the use for
this. The primary reason I came up with rtkit was to allow us to ship PA
and similar software with RT privs out-of-the-box and strictly control
access to RT for that. A command line tool like you seem to suggest does
not really fit into that "out-of-the-box" scheme.

What concerns me a bit here is that RT programs must be written in an
RT specific style to make sense. That means they must internally know
which threads to make RT and which ones not, and when. From the
"outside" of the codebase that is difficult to control, especially since
information about threads in processes is not really available from the
outside on Linux (yes, you can find out about them, but you don't really
know which one is which...).

Also, RT programs must be RT from beginning of their RT code to the
end. If you control their RT scheduling only from the outside this is
almost definitely racy. If you want to control RT privs from outside of the
process, then the only non-racy way would be to use inheriting across an
exec(), which however is something rtkit explcitily prohibits.

I am also wondering how many people would use this functionality instead
of the lower level, chrt(1) command?

So, as mentioned I am not strictly against this, but I'd be interested
to hear some good use cases for this, simply because I fear that people
might otherwise be invited to write improper RT code.

So, convince me!

Lennart

-- 
Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net
http://0pointer.net/lennart/           GnuPG 0x1A015CC4