Re: [Jack-Devel] Multi-user desktop integration

It will be better with the PPA's URL :
https://launchpad.net/~cschieli/+archive/ubuntu/jackaudio

2014-11-02 17:59 GMT+01:00 Cédric Schieli <[hidden]>:

> Hi all,
>
> Nowadays it's quite easy to make PulseAudio and Jack work together, mostly
> thanks to the dbus api, but as soon as a second user enters the scene, by
> means of the user switcher applet, it's once again an inferior user
> experience as compared to what a PulseAudio-only system gives. Generally
> the second user will get no sound at all, other problems arise when the
> second user wants to make use of some Jack applications...
>
> So I've been working lately on making it easier to use Jack as the default
> sound system on a shared workstation, with PulseAudio as a helper for
> desktop sounds. I've investigated 3 solutions which I'll present here.
>
> In all cases it was necessary to have a system-wide Jack server launched
> at boot time. First problem: there is no session dbus available at boot
> time. There are basically 3 ways of solving this:
> 1. use the system dbus instead by faking the DBUS_SESSION_BUS_ADDRESS.
> This will require some modification of system policies to allow the owning
> of the org.freedesktop.ReserveDevice1.Audio0 name
> 2. launch a session bus, which will be used only for this purpose
> 3. hack Jack to allow bypassing the whole thing
> I've chosen 3, the formers do no really reserve anything anyway as the
> buses are not connected to each other. By passing the
> JACK_NO_AUDIO_RESERVATION environment variable I can now disable the
> audio_acquire/audio_release callbacks.
>
> The first solution that comes to mind is to make this system-wide server
> run in promiscuous mode, so I've exported JACK_PROMISCUOUS_SERVER globally
> (in /etc/environment). Problem: for this to work, the server and every
> single Jack application (including the pulse-jack bridge) must be running
> with a 0000 umask, which sounds a bit scary to me. So I've hacked a little
> enhancement to the promiscuous mode which makes it possible to pass the
> name or gid of a group through the JACK_PROMISCUOUS_SERVER variable. In
> that case, the sockets, shared memory segments and semaphores have their
> permissions tightened so only members of that group will get access to
> them. More importantly, it is not needed anymore to fiddle with the umask,
> even if no group is given.
> With that in place, and after having changed the default PulseAudio
> configuration (/etc/pulse/default.pa) to statically load the pulse-jack
> bridge, each user session has its shiny desktop sounds working, and every
> user is able to run Jack applications whenever they want.
>
> One (big) con is that as everybody share the same Jack server the graph
> may easily become incomprehensible (jack_keyboard, jack_keyboard-01,
> jack_keyboard-02, all belonging to different users...). Also, if a user
> start the Jack transport, it will be started for all users !
>
> That's where the two other solutions comes into play (they really are to
> variants of the same solution).
> The idea is to have a main system-wide Jack server in charge of the
> hardware driver, and a second per-user Jack server launched through dbus
> api, connected by some way to the former, and handling the connections with
> the various Jack applications of that user session.
>
> This can easily be implemented by using NetJack bound to the loopback
> interface.
> In this solution, the promiscuous mode is not necessary anymore. The
> netmanager have to be loaded in the main server at boot time, bound to the
> 127.0.0.1 address, with the auto-connect feature enabled. The default.pa
> should use jackdbus-detect and a .config/jack/conf.xml must be put in each
> user's HOME so the net driver is loaded when a Jack server is spawned by
> the user.
>
> Now, each user will only see his/her own applications in the graph, but
> the Jack transport is still unique across the NetJack network. Another
> problem is the overhead introduced by NetJack.
>
> To address these, I've hacked a new JackProxyDriver which is similar to
> the JackNetDriver, but only uses plain Jack API to talk to its upstream
> server so the overhead is reduced to its minimum.
> In this solution, the promiscuous mode is again necessary, but only for
> the main server. The per-user server will run in normal mode toward its
> clients, and will use a promiscuous connection to talk to the main server.
> The .config/jack/conf.xml must be changed to load the proxy driver.
>
> Now that I'm happy with the state of my shared desktop I've sent two pull
> request for all the bits described above.
> https://github.com/jackaudio/jack2/pull/77 contains the reservation
> bypass and the promiscuous mode enhancement,
> https://github.com/jackaudio/jack2/pull/78 contains the JackProxyDriver.
>
> If someone is interested to try it out, I've setup a PPA (currently only
> for 14.04) with a jackd2 package based on KXStudio's one.
>
> Comments and suggestions are welcome.
>
> Regards,
>
> Sdrik
>

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