Re: [Qemu-devel] [RFC PATCH] qapi for audio backends

[Eric Blake]

On 06/03/2015 10:48 AM, Kővágó, Zoltán wrote:
> This is a proposal to add structures into qapi-schema.json to replace the
> existing configuration structures used by audio backends currently. I'm going 
> to
> use it to implement a new way to specify audio backend options (an -audiodev
> command line option, instead of environment variables. This will also allow us
> to use multiple audio backends in one qemu instance), so the structure used 
> here
> will be the basis of the command line syntax.
> 
> This is currently more or less a direct translation of the current audio 
> backend
> options. I've changed some names, trying to accomplish a more consistent 
> naming
> scheme. I wouldn't be surprised if there were options that doesn't work if you
> set their value to anything other than the default (for example, log to 
> monitor
> can crash qemu, QEMU_DSOUND_RESTOURE_RETRIES has a typo, so probably nobody 
> used
> it, etc). I've also tried to reduce copy-paste, when the same set of options 
> can
> be given to output and input (QEMU_*_DAC_* and QEMU_*_ADC_* options), also 
> using
> in and out instead of ADC and DAC, as in the world of SPDIF and HDMI it's
> completely possible that your computer has nothing to do with analog 
> converters.
> Plus a non technician user probably has no idea what ADC and DAC stands for.
> 
> Any comment is appreciated.
> 
> Signed-off-by: Kővágó, Zoltán <address@hidden>
> ---
>  qapi-schema.json | 330 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 330 insertions(+)
> 
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 0662a9b..ff67d5a 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -3769,3 +3769,333 @@
>  # Since: 2.1
>  ##
>  { 'command': 'rtc-reset-reinjection' }
> +
> +##
> +# @AudiodevNoneOptions
> +#
> +# The dummy audio backend has no options.
> +#
> +# Since: XXX

It's okay to tentatively put 2.4 here, if you are aiming for 2.4.  If
you think it will be a big enough project to miss the current release
window, put 2.5.

> +##
> +{ 'struct': 'AudiodevNoneOptions',
> +  '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.
> +#
> +# @period_size_usec: #optional the period size in microseconds. Must not be
> +#                    specified with @period_size_frames.
> +#
> +# @period_size_frames: #optional the period size in frames. Must not be
> +#                      specified with @period_size_usec.
> +#
> +# @buffer_size_usec: #optional the buffer size in microseconds. Must not be
> +#                    specified with @buffer_size_frames.
> +#
> +# @buffer_size_frames: #optional the buffer size in frames. Must not be
> +#                      specified with @buffer_size_usec.

Can we name these with s/_/-/?  We've documented that QMP prefers dash
unless there is compelling reason or consistency to worry about, and I
don't see the compelling reason here.

> +#
> +# Since: XXX
> +##
> +{ 'struct': 'AudiodevAlsaPerDirectionOptions',
> +  'data': {
> +    '*dev':                'str',
> +    '*period_size_usec':   'int',
> +    '*period_size_frames': 'int',
> +    '*buffer_size_usec':   'int',
> +    '*buffer_size_frames': 'int' } }
> +
> +##
> +# @AudiodevAlsaOptions
> +#
> +# Options of the alsa audio backend.
> +#
> +# @in: #optional options of the capture stream.
> +#
> +# @out: #optional options of the playback stream.
> +#
> +# @threshold: #optional

Document this.

> +#
> +# @verbose: #optional behave in a more verbose way
> +#
> +# Since: XXX
> +##
> +{ 'struct': 'AudiodevAlsaOptions',
> +  'data': {
> +    '*in':  'AudiodevAlsaPerDirectionOptions',
> +    '*out': 'AudiodevAlsaPerDirectionOptions',
> +    '*threshold': 'int',
> +    '*verbose':   'bool' } }
> +
> +##
> +# @AudiodevCoreaudioOptions
> +#
> +# Options of the coreaudio backend.
> +#
> +# @buffer_size: #optional size of the buffer in frames
> +#
> +# @buffer_count: #optional number of buffers

Again, dashes would be nicer, if there is no compelling reason otherwise
(I'll quit repeating it).

> +#
> +# Since: XXX

(and I'll quit pointing out XXX in Since lines)

> +##
> +{ 'struct': 'AudiodevCoreaudioOptions',
> +  'data': {
> +    '*buffer_size':  'int',
> +    '*buffer_count': 'int' } }
> +
> +##
> +# @AudiodevDsoundPerDirectionOptions
> +#
> +# Options of the dsound backend that are used for both playback and 
> recording.
> +#
> +# @bufsize: #optional

Document this

> +#
> +# Since: XXX
> +##
> +{ 'struct': 'AudiodevDsoundPerDirectionOptions',
> +  'data' : {
> +    '*bufsize': 'int' } }
> +
> +##
> +# @AudiodevDsoundOptions
> +#
> +# Options of the dsound audio backend.
> +#
> +# @in: #optional options of the capture stream.
> +#
> +# @out: #optional options of the playback stream.
> +#
> +# @lock_retries: #optional number of times to attempt locking the buffer
> +#
> +# @restore_retries: #optional number of times to attempt restoring the buffer
> +#
> +# @getstatus_retries: #optional number of times to attempt getting status of 
> the

Borders on being a long line (yes, it's exactly 80, but I tend to stick
to < 80)

> +#                     buffer
> +#
> +# @set_primary: #optional set the parameters of primary buffer
> +#
> +# @latency_millis: #optional
> +#
> +# @primary_freq: #optional primary buffer frequency
> +#
> +# @primary_channels: #optional primary buffer number of channels
> +#
> +# @primary_format: #optional primary buffer format
> +#
> +# Since: XXX
> +##
> +{ 'struct': 'AudiodevDsoundOptions',
> +  'data': {
> +    '*in':                'AudiodevDsoundPerDirectionOptions',
> +    '*out':               'AudiodevDsoundPerDirectionOptions',
> +    '*lock_retries':      'int',
> +    '*restore_retries':   'int',
> +    '*getstatus_retries': 'int',
> +    '*set_primary':       'bool',
> +    '*latency_millis':    'int',
> +    '*primary_freq':      'int',
> +    '*primary_channels':  'int',
> +    '*primary_format':    'AudioFormat' } }
> +
> +##
> +# @AudiodevOssPerDirectionOptions
> +#
> +# Options of the oss backend that are used for both playback and recording.
> +#
> +# @dev: #optional path of the oss device
> +#
> +# Since: XXX
> +##
> +{ 'struct': 'AudiodevOssPerDirectionOptions',
> +  'data': {
> +    '*dev': 'str' } }
> +
> +##
> +# @AudiodevOssOptions
> +#
> +# Options of the oss audio backend.
> +#
> +# @in: #optional options of the capture stream.
> +#
> +# @out: #optional options of the playback stream.
> +#
> +# @fragsize: #optional fragment size in bytes
> +#
> +# @frags: #optional number of fragments
> +#
> +# @mmap: #optional try using memory mapped access
> +#
> +# @exclusive: #optional open device in exclusive mode (vmix wont work)
> +#
> +# @dsp_policy: #optional set the timing policy of the device, -1 to use 
> fragment
> +#              mode (option ignored on some platforms)
> +#
> +# @debug: #optional turn on some debugging messages
> +#
> +# Since: XXX
> +##
> +{ 'struct': 'AudiodevOssOptions',
> +  'data': {
> +    '*in':         'AudiodevOssPerDirectionOptions',
> +    '*out':        'AudiodevOssPerDirectionOptions',
> +    '*fragsize':   'int',
> +    '*frags':      'int',
> +    '*mmap':       'bool',
> +    '*exclusive':  'bool',
> +    '*dsp_policy': 'int',
> +    '*debug':      'bool' } }
> +
> +##
> +# @AudiodevPaOptions
> +#
> +# Options of the pa audio backend.
> +#
> +# @samples: #optional buffer size in samples
> +#
> +# @server: #optional PulseAudio server address

Worth mentioning that 'pa' == PulseAudio earlier in the docs?

> +#
> +# @sink: #optional sink device name
> +#
> +# @source: #optional source device name
> +#
> +# Since: XXX
> +##
> +{ 'struct': 'AudiodevPaOptions',
> +  'data': {
> +    '*samples': 'int',
> +    '*server':  'str',
> +    '*sink':    'str',
> +    '*source':  'str' } }
> +
> +##
> +# @AudiodevSdlOptions
> +#
> +# Options of the sdl audio backend. (Note that most options are only 
> changeable
> +# through SDL's environment variables).
> +#
> +# @samples: #optional size of SDL buffer in samples
> +#
> +# Since: XXX
> +##
> +{ 'struct': 'AudiodevSdlOptions',
> +  'data': {
> +    '*samples': 'int' } }
> +
> +##
> +# @AudiodevSpiceOptions
> +#
> +# The spice audio backend has no options.
> +#
> +# Since: XXX
> +##
> +{ 'struct': 'AudiodevSpiceOptions',
> +  'data': { } }
> +
> +##
> +# @AudiodevWavOptions
> +#
> +# Options of the wav audio backend.
> +#
> +# @frequency: #optional frequency of the wav file
> +#
> +# @format: #optional sample format of the wav file
> +#
> +# @channels: #optional number of channels of the wav file
> +#
> +# @path: #optional path of the wav file to record.
> +#
> +# Since: XXX
> +##
> +{ 'struct': 'AudiodevWavOptions',
> +  'data': {
> +    '*frequency': 'int',
> +    '*format':    'AudioFormat',
> +    '*channels':  'int',
> +    '*path':       'str' } }

Inconsistent indentation.

> +
> +
> +##
> +# @AudiodevBackendOptions
> +#
> +# A discriminated record of audio backends.
> +#
> +# Since: XXX
> +##
> +{ 'union': 'AudiodevBackendOptions',
> +  'data': {
> +    'none':      'AudiodevNoneOptions',
> +    'alsa':      'AudiodevAlsaOptions',
> +    'coreaudio': 'AudiodevCoreaudioOptions',
> +    'dsound':    'AudiodevDsoundOptions',
> +    'oss':       'AudiodevOssOptions',
> +    'pa':        'AudiodevPaOptions',
> +    'sdl':       'AudiodevSdlOptions',
> +    'spice':     'AudiodevSpiceOptions',
> +    'wav':       'AudiodevWavOptions' } }

AudiodevNoneOptions and AudiodevSpiceOptions are identical; you could
consolidate them into one struct.  I'd also (someday) like to get to the
point of using anonymous structures in a union, particularly when the
variant adds no additional fields, so that you could do:

'data': {
  'none': {},
  'alsa': 'AudiodevAlsaOptions', ...

but don't know if that is worth doing any sooner than Markus can land
his introspection patches.

> +
> +##
> +# @AudioFormat
> +#
> +# An enumeration of possible audio formats.
> +#
> +# Since: XXX
> +##
> +{ '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 fortmat to use when using fixed settings
> +#
> +# @try_poll: #optional attempt to use poll mode
> +#
> +# Since: XXX
> +##
> +{ 'struct': 'AudiodevPerDirectionOptions',
> +  'data': {
> +    '*fixed_settings': 'bool',
> +    '*frequency':      'int',
> +    '*channels':       'int',
> +    '*format':         'AudioFormat',
> +    '*try_poll':       'bool' } }
> +
> +##
> +# @Audiodev
> +#
> +# Captures the configuration of an audio backend.
> +#
> +# @id: identifier of the backend.

Inconsistent on whether you end with '.' (but the whole file is already
that inconsistent, so not too much of a worry)

> +#
> +# @in: #optional options of the capture stream.
> +#
> +# @out: #optional options of the playback stream.
> +#
> +# @timer_period: #optional timer period in HZ (0 - use lowest possible)
> +#
> +# @plive: #optional
> +#
> +# @opts: audio backend specific options
> +#
> +# Since XXX
> +##
> +{ 'struct': 'Audiodev',
> +  'data': {
> +    'id':            'str',
> +    '*in':           'AudiodevPerDirectionOptions',
> +    '*out':          'AudiodevPerDirectionOptions',
> +    '*timer_period': 'int',
> +    '*plive':        'bool',
> +    'opts':          'AudiodevBackendOptions' } }
> 

Overall looks fairly reasonable. Is it enough structures to be worth
splitting into a new qapi/audio.json file and merely touch
qapi-schema.json to add an include?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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