Re: [PATCH v8 03/12] virtio-sound: handle control messages and streams

[Philippe Mathieu-Daudé]

Hi Emmanouil,

On 28/8/23 21:55, Emmanouil Pitsidianakis wrote:
> Receive guest requests in the control (CTRL) queue of the virtio sound
> device and reply with a NOT SUPPORTED error to all control commands.
>
> The receiving handler is virtio_snd_handle_ctrl(). It stores all control
> messages in the queue in the device's command queue. Then it calls
> virtio_snd_process_cmdq() to handle each message.
>
> The handler is process_cmd() which replies with VIRTIO_SND_S_NOT_SUPP.
>
> Based-on: 
> https://github.com/OpenSynergy/qemu/commit/5a2f350eec5d157b90d9c7b40a8e603f4da92471
> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
> Signed-off-by: Igor Skalkin <Igor.Skalkin@opensynergy.com>
> Signed-off-by: Anton Yakovlev <Anton.Yakovlev@opensynergy.com>
> Signed-off-by: Emmanouil Pitsidianakis <manos.pitsidianakis@linaro.org>
> ---
>   hw/virtio/trace-events         |   4 +
>   hw/virtio/virtio-snd.c         | 227 ++++++++++++++++++++++++++++++++-
>   include/hw/virtio/virtio-snd.h |  70 +++++++++-
>   3 files changed, 292 insertions(+), 9 deletions(-)


>   /*
> - * Queue handler stub.
> + * The actual processing done in virtio_snd_process_cmdq().
> + *
> + * @s: VirtIOSound device
> + * @cmd: control command request
> + */
> +static inline void
> +process_cmd(VirtIOSound *s, virtio_snd_ctrl_command *cmd)
> +{
> +    size_t sz = iov_to_buf(cmd->elem->out_sg,
> +                           cmd->elem->out_num,
> +                           0,
> +                           &cmd->ctrl,
> +                           sizeof(cmd->ctrl));
> +    if (sz != sizeof(cmd->ctrl)) {
> +        qemu_log_mask(LOG_GUEST_ERROR,
> +                "%s: virtio-snd command size incorrect %zu vs \
> +                %zu\n", __func__, sz, sizeof(cmd->ctrl));
> +        return;
> +    }
> +
> +    trace_virtio_snd_handle_code(cmd->ctrl.code,
> +                                 print_code(cmd->ctrl.code));
> +
> +    switch (cmd->ctrl.code) {
> +    case VIRTIO_SND_R_JACK_INFO:
> +    case VIRTIO_SND_R_JACK_REMAP:
> +        qemu_log_mask(LOG_UNIMP,
> +                     "virtio_snd: jack functionality is unimplemented.");
> +        cmd->resp.code = VIRTIO_SND_S_NOT_SUPP;
> +        break;
> +    case VIRTIO_SND_R_PCM_INFO:
> +    case VIRTIO_SND_R_PCM_SET_PARAMS:
> +    case VIRTIO_SND_R_PCM_PREPARE:
> +    case VIRTIO_SND_R_PCM_START:
> +    case VIRTIO_SND_R_PCM_STOP:
> +    case VIRTIO_SND_R_PCM_RELEASE:
> +        cmd->resp.code = VIRTIO_SND_S_NOT_SUPP;
> +        break;
> +    case VIRTIO_SND_R_CHMAP_INFO:
> +        qemu_log_mask(LOG_UNIMP,
> +                     "virtio_snd: chmap info functionality is unimplemented.");
> +        trace_virtio_snd_handle_chmap_info();
> +        cmd->resp.code = VIRTIO_SND_S_NOT_SUPP;
> +        break;
> +    default:
> +        /* error */
> +        error_report("virtio snd header not recognized: %"PRIu32,
> +                     cmd->ctrl.code);
> +        cmd->resp.code = VIRTIO_SND_S_BAD_MSG;
> +    }
> +
> +    iov_from_buf(cmd->elem->in_sg,
> +                 cmd->elem->in_num,
> +                 0,
> +                 &cmd->resp,
> +                 sizeof(cmd->resp));
> +    virtqueue_push(cmd->vq, cmd->elem, sizeof(cmd->elem));
> +    virtio_notify(VIRTIO_DEVICE(s), cmd->vq);

I have very few understanding of virtio, but I'm wondering here,
since this function is called under cmdq_mutex(), could it be
useful to batch the queue by calling virtio_notify() only once
in the caller once the whole cmdq is processed ...

> +}
> +
> +/*
> + * Consume all elements in command queue.
> + *
> + * @s: VirtIOSound device
> + */
> +static void virtio_snd_process_cmdq(VirtIOSound *s)
> +{
> +    virtio_snd_ctrl_command *cmd;
> +
> +    if (unlikely(qatomic_read(&s->processing_cmdq))) {
> +        return;
> +    }
> +
> +    WITH_QEMU_LOCK_GUARD(&s->cmdq_mutex) {
> +        qatomic_set(&s->processing_cmdq, true);
> +        while (!QTAILQ_EMPTY(&s->cmdq)) {
> +            cmd = QTAILQ_FIRST(&s->cmdq);
> +
> +            /* process command */
> +            process_cmd(s, cmd);
> +
> +            QTAILQ_REMOVE(&s->cmdq, cmd, next);
> +
> +            g_free(cmd);
> +        }

... here?

> +        qatomic_set(&s->processing_cmdq, false);
> +    }
> +}