Re: Question about virtio_alloc_virtqueues

Hi,
  Looking at the code, it looks like that comment was written at a time
where per-virtqueue MSIX interrupts were not available, and
virtio_alloc_virtqueues() API was already designed to receive a flag to
indicate that per-virtqueue MSIX interrupts were requested. The code you
quoted would likely have been a simple placeholder, to be replaced with
something like "flags |= VIRTIO_PERVQ_INTR" once the support had come. It's
a very common pattern to start with setting flags = 0, and then bitwise or
|= flags depending on the situation.

However:

   - per-virtqueue MSIX interrupts are now available (e.g. look at
   vtpci_setup_interrupts()), and
   - virtiqueues interrupt setup happens in a separate API, i.e.
   virtio_setup_intr(), which takes care all the possible cases

So as far as I can tell that comment is not relevant anymore and can be
removed together with the flags.
Unless I'm wrong, ofc.

Cheers,
  Vincenzo

Il giorno ven 8 set 2023 alle ore 21:05 Mina Galić <freebsd@igalic.co> ha
scritto:

> Hi folks,
>
> for the past two or so weeks, I've been trying to document the
> virtio functions: You can see some of my progress here:
>
> https://codeberg.org/meena/freebsd-src/commits/branch/improve/virtio
>
> I'm currently trying to document virtio_alloc_virtqueues.
> The second argument, flags, is only ever called with 0, and
> never passed on to anything. So I thought I'd remove it.
> However, there *is* this comment in if_vtnet.c:
>
>         /*
>          * TODO: Enable interrupt binding if this is multiqueue. This will
>          * only matter when per-virtqueue MSIX is available.
>          */
>         if (sc->vtnet_flags & VTNET_FLAG_MQ)
>                 flags |= 0;
>
>
> after which flags are still set to 0. for now??
> What does this mean?
>
> Kind regards,
>
> Mina Galić
>
>