Re: [PATCH v8 10/12] virtio-sound: implement audio output (TX)

["Alex Bennée" <alex.bennee@linaro.org>]

Emmanouil Pitsidianakis <manos.pitsidianakis@linaro.org> writes:

> Handle output IO messages in the transmit (TX) virtqueue.
>
> It allocates a VirtIOSoundPCMBlock for each IO message and copies the
> data buffer to it. When the IO buffer is written to the host's sound
> card, the guest will be notified that it has been consumed.
>
> The lifetime of an IO message is:
>
> 1. Guest sends IO message to TX virtqueue.
> 2. QEMU adds it to the appropriate stream's IO buffer queue.
> 3. Sometime later, the host audio backend calls the output callback,
>    virtio_snd_pcm_out_cb(), which is defined with an AUD_open_out()
>    call. The callback gets an available number of bytes the backend can
>    receive. Then it writes data from the IO buffer queue to the backend.
>    If at any time a buffer is exhausted, it is returned to the guest as
>    completed.
> 4. If the guest releases the stream, its buffer queue is flushed by
>    attempting to write any leftover data to the audio backend and
>    releasing all IO messages back to the guest. This is how according to
>    the spec the guest knows the release was successful.
>
> Based-on: https://github.com/OpenSynergy/qemu/commit/5a2f350eec5d157b90d9c7b40a8e603f4da92471
> Signed-off-by: Igor Skalkin <Igor.Skalkin@opensynergy.com>
> Signed-off-by: Anton Yakovlev <Anton.Yakovlev@opensynergy.com>
> Signed-off-by: Emmanouil Pitsidianakis
> <manos.pitsidianakis@linaro.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro