[arch-proaudio] Introducing: dedicated realtime group (not only for jack/jack2)

Jimi Bove jimijames.bove at gmail.com
Mon Jul 30 17:44:30 UTC 2018

So, I don't mean to butt into this discussion or anything, but I was
investigating the files the realtime-privileges package added to my system
to make sure I was doing everything right, and I found what may be a typo?

In /usr/lib/udev/rules.d/40-realtime-privileges.rules, line 4:
KERNEL=="rtc0", GROUP="realtimrealtimee"

That's supposed to say "realtime", not "realtimrealtimee", right?

On Mon, Jul 30, 2018 at 4:34 AM, David Runge <dave at sleepmap.de> wrote:

> On 2018-07-29 18:52:36 (-0400), bill-auger wrote:
> > can you explain why a new group was needed? why remove functionality
> > from the audio group - that is the commonly expected purpose of the
> > audio group on every distro i have used that caters to A/V use-cases -
> > conversely, what purpose would the audio group now serve?
> The audio group is installed via syusers.d with the systemd package
> (defined in /usr/lib/sysusers.d/basic.conf).
> It's one of the system's default groups, which grants access to
> /dev/audio and /dev/snd/* [1] (/dev/rtc0, mentioned last, got dropped in
> by jack/jack2 a few years back). The accompanying udev rule can be found
> in /usr/lib/udev/rules.d/50-udev-default.rules (also part of the systemd
> package). Traditionally, other software installing own rules, relies on
> this group and its settings (e.g. libffado, as found in
> /usr/lib/udev/rules.d/60-ffado.rules).
> The compromise introduced a long time ago for the jack and jack2
> packages (as described upstream on the realtime topic [2]) also relies
> on the audio group.
> However, acquiring realtime privileges and accessing audio hardware are
> two separate things. Note, that while acquiring realtime privileges can
> be benificial for pro-audio applications, it is not the only use-case!
> To make things more clear:
> audio - access specific audio hardware
> realtime - acquire realtime privileges (which you can use for pro-audio)
> > most such distros (including the arch derivative i use) also have a
> > package which is usually named similarly to 'proaudio-settings', that
> > depends on JACK and the kernel-rt and provides optimizations for
> > real-time audio use - but the JACK package should not require the
> > kernel-rt nor any privileges or optimizations; simply because JACK
> > itself does not require those and is intended to be fully usable
> > without them
> That's exactly why the realtime group will exist and realtime-privileges
> will become an optional dependency for jack and jack2.
> It doesn't make any sense to have realtime-privileges depend on linux-rt
> and or jack/jack2, as realtime-privileges is meant to extend the
> capabilities of what a certain user group is allowed to achieve with the
> system (and the system's hardware) and therefore is an extension of what
> said group can achieve with linux-rt and/or jack/jack2.
> > i proposed before the idea of maintaining a consistent
> > 'proaudio-settings' optimizations package in the arch upstream - does
> > this 'realtime-privilege' package do nothing more than create
> > 'realtime' group, with no other optimizations? - if it also has other
> > general optimizations for real-time audio, then i suggest it be
> > renamed to a commonly recognizable name like: 'proaudio-settings' - if
> > not, then i still propose such a 'proaudio-settings' optimization
> > package - such a package would necessarily depend on JACK and the
> > 'realtime-privilege' package - but that would make it clear that it is
> > the optimization package that provides realtime privileges and not the
> > JACK package
> The "optimizations" (which are more capabilities given to the realtime
> group) are now all in the realtime-privileges package, instead of
> redundantly packaged in jack/jack2 and being bound to the audio group
> (which is there for accessing audio hardware, not for acquiring realtime
> privileges).
> Again: Acquiring realtime is not a pro-audio only thing.
> jack/jack2 can work without acquiring realtime (mind [2]). However, one
> can extend reliability of some software by acquiring realtime
> privileges. Therefore it makes no sense to have separate settings for
> pro-audio, as realtime-privileges is a more general approach to whatever
> one wants to achieve with that.
> In other words: You wouldn't want to have to install jack/jack2 just to
> acquire realtime privileges for another piece of software, that is non
> pro-audio related, but you can now optionally extend jack/jack2's
> capabilities by using realtime-privileges (with a more clear
> distinction as to what the groups you're in actually stand for).
> I hope this answers your questions.
> Best,
> David
> [1] https://wiki.archlinux.org/index.php/Users_and_groups#
> Pre-systemd_groups
> [2] http://jackaudio.github.io/faq/linux_rt_config.html
> --
> https://sleepmap.de
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