[ sorry for the bogus original subject ]
Alan Cox <alan@lxorguk.ukuu.org.uk> wrote
>> perhaps you can explain how an audio application with a GUI that needs
>> to take advantage of SCHED_FIFO in some subset of its threads, and/or
>> mlock(2), can be run without suid (or sudo, though it seems that the
>> problems there are pretty similar) ?
>
>Capabilities let you control which you get. The normal approach is to run
>the X11 interface unpriviledged - after all it is just display not real time
>tied. When you get to video playback you get X and stuff involved and it
>does get harder.
What do I start reading to catch up on capabilities ?
---------
Aaron Denney < wnoise@ugcs.caltech.edu> wrote:
>SCHED_FIFO can be done with a 18-line suid helper wrapper. I don't
Sorry, it can't. You're assuming that the target app is single
threaded. The apps I'm talking about are multithreaded, and only some
of them should run SCHED_FIFO.
>see why it couldn't fork() and exec() a helper app to mlock() a shared
>memory segment for audio data buffering.
Unfortunately, I didn't mean what I said: mlockall(2), not
mlock(2). Locking down the audio buffer when the text can still be
paged tends to not accomplish the desired effect.
And using IPC for low latency real-time audio tends to not work very
well. I think you're confusing apps like xmms with the demands of
multichannel disk recording, heavy duty software synthesis, etc.
>(No, that won't let you mlock in the code, etc. For that, you do need
>suid.)
Exactly.
--p
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