Re: [PATCH 3/8] virtio_blk_process_queued_requests: always run in a bh

[Stefan Hajnoczi]

On Thu, Jun 09, 2022 at 10:37:22AM -0400, Emanuele Giuseppe Esposito wrote:
> diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
> index f9224f23d2..03e10a36a4 100644
> --- a/hw/block/dataplane/virtio-blk.c
> +++ b/hw/block/dataplane/virtio-blk.c
> @@ -234,8 +234,16 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
>          goto fail_aio_context;
>      }
>  
> +    blk_inc_in_flight(s->conf->conf.blk);

Missing comment explaining why the in-flight counter is incremented and
where the matching decrement operation is located.

I think you can get away without a comment if blk_inc_in_flight() is
right next to aio_bh_new(), but in this case there are a few lines of
code in between and it becomes unclear if there is a connection.

> +    /*
> +     * vblk->bh is only set in virtio_blk_dma_restart_cb, which
> +     * is called only on vcpu start or stop.
> +     * Therefore it must be null.
> +     */
> +    assert(vblk->bh == NULL);
>      /* Process queued requests before the ones in vring */

This comment makes an assumption about the order of file descriptor
handlers vs BHs in the event loop. I suggest removing the comment. There
is no reason for processing queued requests first anyway since
virtio-blk devices can complete requests in any order.

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