On Thursday 02 May 2013 16:37:47 David Henningsson wrote: > On 05/02/2013 04:28 PM, Tvrtko Ursulin wrote: > > Hi David, > > > > On Thursday 02 May 2013 12:55:05 David Henningsson wrote: > >> Just had an idea which I'll write down here before I forget it > >> again...and I'm not saying I'll implement this anytime soon either, but > >> here goes: > >> > >> There is a device reserve protocol between PulseAudio and JACK2 - when > >> JACK needs the sound card, it'll send a dbus message to PulseAudio and > >> grab a name in D-Bus. > >> > >> However, there are plenty of applications who like to access ALSA > >> directly, without going through JACK2 or PulseAudio. By making a > >> "reserve" plugin, we could have this functionality for those apps too. > >> > >> In practice, if the app usually opens "plughw:0" or "hw:0", it could > >> instead open "reserve:plughw:0" or "reserve:hw:0" to also reserve the > >> device from PulseAudio usage while the device is open. Meanwhile, > >> PulseAudio is free to use other audio devices (which is not the case > >> when using e g pasuspender). > >> > >> How does that sound? > > > > If I understand correctly you are saying essentially this: > > > > 1. There is an existing device control protocol which works over DBus. > > 2. Your idea is to add a equivalent device control protocol using ALSA PCM > > plugin (well in fact not add but create a new proxy interface to it). > > > > Is that right? If so, how do you provide this functionality to existing > > applications without teaching them about the reserve plugin? > > Many ALSA applications lets you specify the device string on e g the > command line or through a configuration interface. So the end user would > configure the application to use "reserve:plughw:0" instead of "plughw:0". > > The applications that do not follow this will have to be taught, and > they have a extremely simple way to implement it - just add "reserve:" > do the device string. Ah yes I forgot about this configurability. Which also means the question of central policy is sorted since it is explicit user configuration to steal a device. It is still a bit kludgy for a PCM plugin to do this, but, it solves a real problem and does it cheaply so I think the result justifies the means in this case. Regards, Tvrtko P.S. I am not active in this field but just dropping in due personal interest in this functionality.
