Re: [PATCH v9 2/4] chardev/char-hub: implement backend chardev aggregator

[Markus Armbruster <armbru@redhat.com>]

Roman Penyaev <r.peniaev@gmail.com> writes:

> This patch implements a new chardev backend `hub` device, which
> aggregates input from multiple backend devices and forwards it to a
> single frontend device. Additionally, `hub` device takes the output
> from the frontend device and sends it back to all the connected
> backend devices. This allows for seamless interaction between
> different backend devices and a single frontend interface.
>
> The idea of the change is trivial: keep list of backend devices
> (up to 4), init them on demand and forward data buffer back and
> forth.
>
> The following is QEMU command line example:
>
>    -chardev pty,path=/tmp/pty,id=pty0 \
>    -chardev vc,id=vc0 \
>    -chardev hub,id=hub0,chardevs.0=pty0,chardevs.1=vc0 \
>    -device virtconsole,chardev=hub0 \
>    -vnc 0.0.0.0:0
>
> Which creates 2 backend devices: text virtual console (`vc0`) and a
> pseudo TTY (`pty0`) connected to the single virtio hvc console with
> the backend aggregator (`hub0`) help. `vc0` renders text to an image,
> which can be shared over the VNC protocol.  `pty0` is a pseudo TTY
> backend which provides biderectional communication to the virtio hvc
> console.
>
> 'chardevs.N' list syntax is used for the sake of compatibility with
> the representation of JSON lists in 'key=val' pairs format of the
> util/keyval.c, despite the fact that modern QAPI way of parsing,
> namely qobject_input_visitor_new_str(), is not used. Choice of keeping
> QAPI list syntax may help to smoothly switch to modern parsing in the
> future.
>
> Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
> Reviewed-by: "Marc-André Lureau" <marcandre.lureau@redhat.com>
> Cc: qemu-devel@nongnu.org

[...]

> diff --git a/qapi/char.json b/qapi/char.json
> index e04535435034..f02b66c06b3e 100644
> --- a/qapi/char.json
> +++ b/qapi/char.json
> @@ -332,6 +332,19 @@
>    'data': { 'chardev': 'str' },
>    'base': 'ChardevCommon' }
>  
> +##
> +# @ChardevHub:
> +#
> +# Configuration info for hub chardevs.
> +#
> +# @chardevs: List of chardev IDs, which should be added to this hub

Suggest "IDs to be added".

According to the commit message, there's a limit of four chardevs.
Better document that here.

> +#
> +# Since: 10.0
> +##
> +{ 'struct': 'ChardevHub',
> +  'data': { 'chardevs': ['str'] },
> +  'base': 'ChardevCommon' }
> +
>  ##
>  # @ChardevStdio:
>  #
> @@ -479,6 +492,8 @@
>  #
>  # @mux: (since 1.5)
>  #
> +# @hub: (since 10.0)
> +#
>  # @msmouse: emulated Microsoft serial mouse (since 1.5)
>  #
>  # @wctablet: emulated Wacom Penpartner serial tablet (since 2.9)
> @@ -521,6 +536,7 @@
>              'pty',
>              'null',
>              'mux',
> +            'hub',
>              'msmouse',
>              'wctablet',
>              { 'name': 'braille', 'if': 'CONFIG_BRLAPI' },
> @@ -595,6 +611,16 @@
>  { 'struct': 'ChardevMuxWrapper',
>    'data': { 'data': 'ChardevMux' } }
>  
> +##
> +# @ChardevHubWrapper:
> +#
> +# @data: Configuration info for hub chardevs
> +#
> +# Since: 10.0
> +##
> +{ 'struct': 'ChardevHubWrapper',
> +  'data': { 'data': 'ChardevHub' } }
> +
>  ##
>  # @ChardevStdioWrapper:
>  #
> @@ -703,6 +729,7 @@
>              'pty': 'ChardevPtyWrapper',
>              'null': 'ChardevCommonWrapper',
>              'mux': 'ChardevMuxWrapper',
> +            'hub': 'ChardevHubWrapper',
>              'msmouse': 'ChardevCommonWrapper',
>              'wctablet': 'ChardevCommonWrapper',
>              'braille': { 'type': 'ChardevCommonWrapper',

With the doc nits addressed
Acked-by: Markus Armbruster <armbru@redhat.com>