Re: [RFC] ALSA: vsnd: Add Xen para-virtualized frontend driver

From: Takashi Sakamoto
Date: Thu Nov 02 2017 - 05:44:16 EST


On Oct 30 2017 15:33, Oleksandr Andrushchenko wrote:
This is an attempt to summarize previous discussions on Xen para-virtual
sound driver.

A first attempt has been made to upstream the driver [1] which brought number
of fundamental questions, one of the biggest ones was that the frontend driver
has no means to synchronize its period elapsed event with the host driver,
but uses software emulation on the guest side [2] with a timer.
In order to address this a change to the existing Xen para-virtual sound
protocol [3] was proposed to fill this gap [4] and remove emulation:
1. Introduced a new event channel from back to front
2. New event with number of bytes played/captured (XENSND_EVT_CUR_POS,
to be used for sending snd_pcm_period_elapsed at frontend
(in Linux implementation, sent in bytes, not frames to make the protocol
generic and consistent)
3. New request for playback/capture control (XENSND_OP_TRIGGER) with
start/pause/stop/resume sub-ops.

Along with these changes other comments on the driver were addressed,
e.g. split into smaller chunks, moved the driver from misc to xen etc. [5].

Hope, this helps to get the full picture of what was discussed and makes it
possible to move forward: if the approach seems ok, then I'll start
upstreaming the changes to the sndif protocol and then will send the updated
version of the driver for the further review.

This message has below line in its header.

> In-Reply-To: <e56a09e9-da66-b748-4e82-4b96a18cef32@xxxxxxxxx>

This field is defined in RFC822[1], and recent mail clients use this header field to associate the message to a message which the field indicates. This results in a series of messages, so-called 'message thread'. Iwai-san would like you to start a new message thread for your topic. Would you please post this message again without the header field?

Generally, receiving no reactions means that readers/reviewers don't get enough information for your idea yet. (Of course, there's a probability that your work attracts no one...) In this case, submitting more resources is better, rather than requesting comments to them. For instance, you can point links to backend/frontend implementation as para-virtualization drivers which use the new feature of interface, if you did work for it. Indicating procedure to use a series of your work is better for test, if possible.

[1] https://www.ietf.org/rfc/rfc0822.txt

Regards

Takashi Sakamoto