linux-kernel - Re: [RFC v4 5/5] virtio

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Date:   Wed, 16 May 2018 20:26:21 +0800
From:   Tiwei Bie <tiwei.bie@...el.com>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:     mst@...hat.com, jasowang@...hat.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        wexu@...hat.com, jfreimann@...hat.com
Subject: Re: [RFC v4 5/5] virtio_ring: enable packed ring

On Wed, May 16, 2018 at 02:42:53PM +0300, Sergei Shtylyov wrote:
> On 05/16/2018 01:21 PM, Tiwei Bie wrote:
> 
> >>> Signed-off-by: Tiwei Bie <tiwei.bie@...el.com>
> >>> ---
> >>>   drivers/virtio/virtio_ring.c | 2 ++
> >>>   1 file changed, 2 insertions(+)
> >>>
> >>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> >>> index de3839f3621a..b158692263b0 100644
> >>> --- a/drivers/virtio/virtio_ring.c
> >>> +++ b/drivers/virtio/virtio_ring.c
> >>> @@ -1940,6 +1940,8 @@ void vring_transport_features(struct virtio_device *vdev)
> >>>   			break;
> >>>   		case VIRTIO_F_IOMMU_PLATFORM:
> >>>   			break;
> >>> +		case VIRTIO_F_RING_PACKED:
> >>> +			break;
> >>
> >>    Why not just add this *case* under the previous *case*?
> > 
> > Do you mean fallthrough? Something like:
> > 
> > 		case VIRTIO_F_IOMMU_PLATFORM:
> > 		case VIRTIO_F_RING_PACKED:
> > 			break;
> 
>    Yes, exactly. :-)

Using fallthrough in this case will make the code more
compact. I like such coding style. But unfortunately,
it's not consistent with the existing code. :(

The whole function will become something like this:

void vring_transport_features(struct virtio_device *vdev)
{
	unsigned int i;

	for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
		switch (i) {
		case VIRTIO_RING_F_INDIRECT_DESC:
			break;
		case VIRTIO_RING_F_EVENT_IDX:
			break;
		case VIRTIO_F_VERSION_1:
			break;
		case VIRTIO_F_IOMMU_PLATFORM:
		case VIRTIO_F_RING_PACKED:
			break;
		default:
			/* We don't understand this bit. */
			__virtio_clear_bit(vdev, i);
		}
	}
}

Best regards,
Tiwei Bie

> 
> > Best regards,
> > Tiwei Bie
> 
> [...]
> 
> MBR, Sergei
>