On Tue, 2011-11-01 at 10:11 -0400, Konrad Rzeszutek Wilk wrote: > On Tue, Nov 01, 2011 at 10:19:45AM +0530, Arun Raghavan wrote: > > On Mon, 2011-10-31 at 17:33 +0100, George Boutsioukis wrote: > > > Hello PulseAudio people! > > > > > > > > > As part of a Google Summer of code project for Xen during this summer, > > > I wrote a PulseAudio module that acts as the frontend part of a Xen > > > paravirtualized audio driver. Basically what it does is push audio > > > frames over a ring buffer placed in memory shared between different > > > Xen domains, using Xen's interrupt-like events to notify the playback > > > backend that audio data is available. > > > > Incidentally, Is there a reason you chose not to do this by exposing the > > host server over the network[1] instead of having to invent your own > > protocol for host/guest communication? > > Couple of things: > - security (firewall rules might will to open on the guest/host) > - traffic is mungled along with the other traffic that might have nothing > to do with audio. > - extra configuration setup of making it work - you would need to pass > to the guest the IP of the host, and the host would need to dynamically > add an ACL for the guest. > > One way to make some of these issues disappear is to create a second interface > between host and guest that is private and will only be used for audio traffic. > It won't solve the 'extra configuration' issue. It also will be complex to setup - > both the guest and host have to know which of the interfaces is used for normal > traffic vs audio traffic. > > Making it use the XenBus and using a ring-buffer bypasses a bunch of these > issues - the configuration is negotiated with the XenBus. This means that the host > and guest know where each is (they only have to negotiate the event channel (think > IRQ), and ring reference (think virtual memory for shared page)). > > In regards to the ring implementation the idea behind it is to be the standard > for PV audio. Which means that you can have different backends and frontends using > a different implementation. For Windows, you could write the frontend using DSound > and it would "pass" the audio frames on the ring, while the backend (host) would > pick them up and feed them in PulseAudio. Thanks for the explanation -- does make more sense to make a virtual card and support arbitrary guests. -- Arun
