Re: [PATCH PoC 1/7] QAPI: gpio JSON

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Mar 19, 2025 at 10:57:51AM +0300, Nikita Shubin via B4 Relay wrote:
> From: Nikita Shubin <nshubin@yadro.com>
> 
> Signed-off-by: Nikita Shubin <nshubin@yadro.com>
> ---
>  qapi/gpio.json        | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  qapi/meson.build      |  1 +
>  qapi/qapi-schema.json |  1 +
>  3 files changed, 70 insertions(+)
> 
> diff --git a/qapi/gpio.json b/qapi/gpio.json
> new file mode 100644
> index 0000000000000000000000000000000000000000..1c2b7af36813ff52cbb3a44e64a2e5a5d8658d62
> --- /dev/null
> +++ b/qapi/gpio.json
> @@ -0,0 +1,68 @@
> +# -*- Mode: Python -*-
> +# vim: filetype=python
> +#
> +
> +##
> +# = Gpio devices
> +##
> +
> +##
> +# @GpiodevInfo:
> +#
> +# Information about a gpio device.
> +#
> +# @label: the label of the gpio device
> +#
> +# Since: 9.2
> +##
> +{ 'struct': 'GpiodevInfo',
> +  'data': { 'label': 'str' } }
> +
> +##
> +# @GpiodevBackendKind:
> +#
> +# @chardev: chardevs
> +#
> +# Since: 9.2
> +##
> +{ 'enum': 'GpiodevBackendKind',
> +  'data': [ 'chardev' ] }
> +
> +##
> +# @GpiodevChardev:
> +#
> +# Configuration info for chardev gpiodevs.
> +#
> +# @chardev: chardev id
> +#
> +# @size: buffer size, default is 65536
> +#
> +# Since: 9.2
> +##
> +  { 'struct': 'GpiodevChardev',
> +    'data': { 'chardev': 'str',
> +              '*size': 'int' } }
> +
> +##
> +# @GpiodevChardevWrapper:
> +#
> +# @data: Configuration info for chardev gpiodevs
> +#
> +# Since: 9.2
> +##
> +{ 'struct': 'GpiodevChardevWrapper',
> +  'data': { 'data': 'GpiodevChardev' } }
> +
> +##
> +# @GpiodevBackend:
> +#
> +# Configuration info for the new chardev backend.
> +#
> +# @type: backend type
> +#
> +# Since: 9.2
> +##
> +{ 'union': 'GpiodevBackend',
> +  'base': { 'type': 'GpiodevBackendKind' },
> +  'discriminator': 'type',
> +  'data': { 'chardev': 'GpiodevChardevWrapper' } }

While historically we've just wired things up to chardevs in QEMU,
in most cases this is just a hack to get the ability too configure
a socket, with the other chardev backends being never used. The
downside of this is that chardev APIs internally are not very nice
to work with, especally if you want/need to be aware of client
connection establishment/closure.

These days we've got common socket APIs and QAPI schema available
and can bypass the chardevs (which have a pretty unpleasant
internal API) if all we need is a socket backend connecting to
an external server. This would let code directly work with the
QIOChannelSocket object, instead of that object being hidden
behind the chardev APIs.

 { 'enum': 'GpiodevBackendKind',
   'data': [ 'socket' ] }

 { 'struct': 'GpiodevSocket',
   'data': { 'addr': 'SocketAddress',
             '*size': 'int'} }

 { 'struct': 'GpiodevSocketWrapper',
   'data': { 'data': 'GpiodevSocket' } }


 { 'union': 'GpiodevBackend',
   'base': { 'type': 'GpiodevBackendKind' },
   'discriminator': 'type',
   'data': { 'socket': 'GpiodevSocketWrapper' } }

if you need to switch between client/server mode some further
additions would be needed.


With regards,
Daniel
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