Re: [Qemu-devel] [PATCH v2 1/6] qapi: qapi for audio backends

[Kővágó Zoltán]

2015-06-17 09:46 keltezéssel, Markus Armbruster írta:
> Copying Eric for additional QAPI schema expertise.
>
> My questions inline, pretty sure they show my ignorance.
>
> "Kővágó, Zoltán" <address@hidden> writes:
>
> > This patch adds structures into qapi to replace the existing configuration
> > structures used by audio backends currently. This qapi will be the base of the
> > -audiodev command line parameter (that replaces the old environment variables
> > based config).
> >
> > This is not a 1:1 translation of the old options, I've tried to make them much
> > more consistent (e.g. almost every backend had an option to specify buffer size,
> > but the name was different for every backend, and some backends required usecs,
> > while some other required frames, samples or bytes). Also tried to reduce the
> > number of abbreviations used by the config keys.
> >
> > Some of the more important changes:
> > * use `in` and `out` instead of `ADC` and `DAC`, as the former is more user
> >    friendly imho
> > * moved buffer settings into the global setting area (so it's the same for all
> >    backends that support it. Backends that can't change buffer size will simply
> >    ignore them). Also using usecs, as it's probably more user friendly than
> >    samples or bytes.
> > * try-poll is now an alsa and oss backend specific option (as all other backends
> >    currently ignore it)
> >
> > Signed-off-by: Kővágó, Zoltán <address@hidden>
> >
> > ---
> >
> > Changes from v1 patch:
> > * every time-related field now take usecs (and removed -usecs, -millis suffixes)
> > * fixed inconsisten optional marking, language issues
> >
> > Changes from v2 RFC patch:
> > * in, out are no longer optional
> > * try-poll: moved to alsa and oss (as no other backend used them)
> > * voices: added (env variables had this option)
> > * dsound: removed primary buffer related fields
> >
> > Changes from v1 RFC patch:
> > * fixed style issues
> > * moved definitions into a separate file
> > * documented undocumented options (hopefully)
> > * removed plive option. It was useless even years ago so it can probably safely
> >    go away: 
> > https://lists.nongnu.org/archive/html/qemu-devel/2012-03/msg02427.html
> > * removed verbose, debug options. Backends should use trace events instead.
> > * removed *_retries options from dsound. It's a kludge.
> > * moved buffer_usecs and buffer_count to the global config options. Some driver
> >    might ignore it (as they do not expose API to change them).
> > * wav backend: removed frequecy, format, channels as AudiodevPerDirectionOptions
> >    already have them.
> >
> > Makefile         |   4 +-
> >   qapi-schema.json |   3 +
> >   qapi/audio.json  | 223 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >   3 files changed, 228 insertions(+), 2 deletions(-)
> >   create mode 100644 qapi/audio.json
> >
> > diff --git a/Makefile b/Makefile
> > index 3f97904..ac566fa 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -257,8 +257,8 @@ $(SRC_PATH)/qga/qapi-schema.json 
> > $(SRC_PATH)/scripts/qapi-commands.py $(qapi-py)
> >                 "  GEN   $@")
> >
> >   qapi-modules = $(SRC_PATH)/qapi-schema.json $(SRC_PATH)/qapi/common.json \
> > -               $(SRC_PATH)/qapi/block.json $(SRC_PATH)/qapi/block-core.json \
> > -               $(SRC_PATH)/qapi/event.json
> > +               $(SRC_PATH)/qapi/audio.json  $(SRC_PATH)/qapi/block.json \
> > +               $(SRC_PATH)/qapi/block-core.json $(SRC_PATH)/qapi/event.json
> >
> >   qapi-types.c qapi-types.h :\
> >   $(qapi-modules) $(SRC_PATH)/scripts/qapi-types.py $(qapi-py)
> > diff --git a/qapi-schema.json b/qapi-schema.json
> > index 106008c..e751ea3 100644
> > --- a/qapi-schema.json
> > +++ b/qapi-schema.json
> > @@ -5,6 +5,9 @@
> >   # QAPI common definitions
> >   { 'include': 'qapi/common.json' }
> >
> > +# QAPI audio definitions
> > +{ 'include': 'qapi/audio.json' }
> > +
> >   # QAPI block definitions
> >   { 'include': 'qapi/block.json' }
> >
> > diff --git a/qapi/audio.json b/qapi/audio.json
> > new file mode 100644
> > index 0000000..2851689
> > --- /dev/null
> > +++ b/qapi/audio.json
> > @@ -0,0 +1,223 @@
> > +# -*- mode: python -*-
> > +#
> > +# Copyright (C) 2015 Zoltán Kővágó <address@hidden>
> > +#
> > +# This work is licensed under the terms of the GNU GPL, version 2 or later.
> > +# See the COPYING file in the top-level directory.
> > +
> > +##
> > +# @AudiodevNoOptions
> > +#
> > +# The none, coreaudio, sdl and spice audio backend have no options.
> > +#
> > +# Since: 2.4
> > +##
> > +{ 'struct': 'AudiodevNoOptions',
> > +  'data': { } }
> > +
> > +##
> > +# @AudiodevAlsaPerDirectionOptions
> > +#
> > +# Options of the alsa backend that are used for both playback and recording.
> > +#
> > +# @dev: #optional the name of the alsa device to use
>
> Who picks the default, QEMU or ALSA?

It defaults to "default", which tells alsa to use the default device...

> > +#
> > +# @try-poll: #optional attempt to use poll mode
>
> What happens when the attempt fails?

It falls back to non polling (timer based) mode.

> > +#
> > +# Since: 2.4
> > +##
> > +{ 'struct': 'AudiodevAlsaPerDirectionOptions',
> > +  'data': {
> > +    '*dev':      'str',
> > +    '*try-poll': 'bool' } }
> > +
> > +##
> > +# @AudiodevAlsaOptions
> > +#
> > +# Options of the alsa audio backend.
> > +#
> > +# @in: options of the capture stream
> > +#
> > +# @out: options of the playback stream
> > +#
> > +# @threshold: #optional set the threshold (in frames) when playback starts
> > +#
> > +# Since: 2.4
> > +##
> > +{ 'struct': 'AudiodevAlsaOptions',
> > +  'data': {
> > +    'in':         'AudiodevAlsaPerDirectionOptions',
> > +    'out':        'AudiodevAlsaPerDirectionOptions',
> > +    '*threshold': 'int' } }
>
> Do we have an established term for a "direction"?
>
> If not: the use with 'in' and 'out' tempts me to name the type
> AudiodevAlsaIOOptions.
>
> Just rambling, use what you think is best.

I don't know, so far nobody rambled about my naming...

> > +
> > +##
> > +# @AudiodevDsoundOptions
> > +#
> > +# Options of the dsound audio backend.
> > +#
> > +# @latency: #optional add extra latency to playback (in microseconds)
>
> We already use seconds, milliseconds and nanoseconds.  You make the zoo
> complete.

Hmm. The audio backend previously used microseconds, milliseconds, 
Hertz, frames, samples and bytes as time measurement, now at least 
everything use microseconds. Milliseconds precision is not enough, while 
nanosecond precision doesn't really make sense imho.

> > +#
> > +# Since: 2.4
> > +##
> > +{ 'struct': 'AudiodevDsoundOptions',
> > +  'data': {
> > +    '*latency': 'int' } }
> > +
> > +##
> > +# @AudiodevOssPerDirectionOptions
> > +#
> > +# Options of the oss backend that are used for both playback and recording.
> > +#
> > +# @dev: #optional path of the oss device
>
> Who picks the default, QEMU or OSS?

It defaults to "/dev/dsp".

> For ALSA, you documented @dev to be "the name", here it's "path".
> Intentional difference?

Yes. For oss you have to provide a filesystem path of the audio device 
(like /dev/dsp), for alsa you provide an alsa specific name, like 
"default", "hw:1,0", "hdmi:CARD=NVidia,DEV=1", whatever.

> > +#
> > +# @try-poll: #optional attempt to use poll mode
> > +#
> > +# Since: 2.4
> > +##
> > +{ 'struct': 'AudiodevOssPerDirectionOptions',
> > +  'data': {
> > +    '*dev':      'str',
> > +    '*try-poll': 'bool' } }
>
> Same as for ALSA.  Keeping them separate is fine with me.

This is the same as alsa's try-poll. They're separate because only these 
two backend use this setting.
> > +
> > +##
> > +# @AudiodevOssOptions
> > +#
> > +# Options of the oss audio backend.
> > +#
> > +# @in: options of the capture stream
> > +#
> > +# @out: options of the playback stream
> > +#
> > +# @mmap: #optional try using memory mapped access
>
> What happens when the attempt fails?

It should fall back to non-mmapped access (should because when I 
checked, it was buggy, at least on linux with alsa emulated oss on 
pulseaudio alsa device...)

> Should this be called try-mmap?
Agree.

> > +#
> > +# @exclusive: #optional open device in exclusive mode (vmix won't work)
> > +#
> > +# @dsp-policy: #optional set the timing policy of the device, -1 to use 
> > fragment
> > +#              mode (option ignored on some platforms)
>
> What are the possible values besides -1?

It should be a number between 0 and 10 (according to this page: 
http://manuals.opensound.com/developer/SNDCTL_DSP_POLICY.html)

> > +#
> > +# Since: 2.4
> > +##
> > +{ 'struct': 'AudiodevOssOptions',
> > +  'data': {
> > +    'in':          'AudiodevOssPerDirectionOptions',
> > +    'out':         'AudiodevOssPerDirectionOptions',
> > +    '*mmap':       'bool',
> > +    '*exclusive':  'bool',
> > +    '*dsp-policy': 'int' } }
> > +
> > +##
> > +# @AudiodevPaOptions
> > +#
> > +# Options of the pa (PulseAudio) audio backend.
> > +#
> > +# @server: #optional PulseAudio server address
> > +#
> > +# @sink: #optional sink device name
> > +#
> > +# @source: #optional source device name
>
> Who picks the defaults, QEMU or PA?

PA

> > +#
> > +# Since: 2.4
> > +##
> > +{ 'struct': 'AudiodevPaOptions',
> > +  'data': {
> > +    '*server': 'str',
> > +    '*sink':   'str',
> > +    '*source': 'str' } }
> > +
> > +##
> > +# @AudiodevWavOptions
> > +#
> > +# Options of the wav audio backend.
> > +#
> > +# @path: #optional path of the wav file to record
> > +#
> > +# Since: 2.4
> > +##
> > +{ 'struct': 'AudiodevWavOptions',
> > +  'data': {
> > +    '*path': 'str' } }
>
> Who picks the default?

It defaults to "qemu.wav"

> > +
> > +
> > +##
> > +# @AudiodevBackendOptions
> > +#
> > +# A discriminated record of audio backends.
> > +#
> > +# Since: 2.4
> > +##
> > +{ 'union': 'AudiodevBackendOptions',
> > +  'data': {
> > +    'none':      'AudiodevNoOptions',
> > +    'alsa':      'AudiodevAlsaOptions',
> > +    'coreaudio': 'AudiodevNoOptions',
> > +    'dsound':    'AudiodevDsoundOptions',
> > +    'oss':       'AudiodevOssOptions',
> > +    'pa':        'AudiodevPaOptions',
> > +    'sdl':       'AudiodevNoOptions',
> > +    'spice':     'AudiodevNoOptions',
> > +    'wav':       'AudiodevWavOptions' } }
> > +
> > +##
> > +# @AudioFormat
> > +#
> > +# An enumeration of possible audio formats.
> > +#
> > +# Since: 2.4
> > +##
> > +{ 'enum': 'AudioFormat',
> > +  'data': [ 'u8', 's8', 'u16', 's16', 'u32', 's32' ] }
> > +
> > +##
> > +# @AudiodevPerDirectionOptions
> > +#
> > +# General audio backend options that are used for both playback and recording.
> > +#
> > +# @fixed-settings: #optional use fixed settings for host DAC/ADC
> > +#
> > +# @frequency: #optional frequency to use when using fixed settings
> > +#
> > +# @channels: #optional number of channels when using fixed settings
> > +#
> > +# @format: #optional sample format to use when using fixed settings
>
> Are these guys used when @fixed-settings is off?

No.

> > +#
> > +# @buffer: #optional the buffer size (in microseconds)
>
> @buffer suggests this is a buffer, not a buffer length given as time
> span.  @buffer-len?

Ok. (It used to be called buffer-usecs before I changed everything to 
microseconds.)

> > +#
> > +# @buffer-count: #optional number of buffers
> > +#
> > +# Since: 2.4
> > +##
> > +{ 'struct': 'AudiodevPerDirectionOptions',
> > +  'data': {
> > +    '*fixed-settings': 'bool',
> > +    '*frequency':      'int',
> > +    '*channels':       'int',
> > +    '*voices':         'int',
> > +    '*format':         'AudioFormat',
> > +    '*buffer':         'int',
> > +    '*buffer-count':   'int' } }
> > +
> > +##
> > +# @Audiodev
> > +#
> > +# Captures the configuration of an audio backend.
> > +#
> > +# @id: identifier of the backend
> > +#
> > +# @in: options of the capture stream
> > +#
> > +# @out: options of the playback stream
> > +#
> > +# @timer-period: #optional timer period (in microseconds, 0: use lowest
> > +#                possible)
> > +#
> > +# @opts: audio backend specific options
> > +#
> > +# Since: 2.4
> > +##
> > +{ 'struct': 'Audiodev',
> > +  'data': {
> > +    '*id':           'str',
> > +    'in':            'AudiodevPerDirectionOptions',
> > +    'out':           'AudiodevPerDirectionOptions',
> > +    '*timer-period': 'int',
> > +    'opts':          'AudiodevBackendOptions' } }
>
> Have you considered making this a flat union, similar ro
> BlockdevOptions?

Not really. If you qapi masters out there think it's better, then I will 
convert it.

> Don't get deceived by the number of my questions, this is solid work.