netdev - Re: [PATCH v9 08/32] virtio_ring: split: extract the logic of attach vring

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Date:   Wed, 13 Apr 2022 14:44:04 +0800
From:   Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Jeff Dike <jdike@...toit.com>, Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        Vadim Pasternak <vadimp@...dia.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Cornelia Huck <cohuck@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        linux-um@...ts.infradead.org, netdev@...r.kernel.org,
        platform-driver-x86@...r.kernel.org,
        linux-remoteproc@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, bpf@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v9 08/32] virtio_ring: split: extract the logic of attach vring

On Tue, 12 Apr 2022 11:31:08 +0800, Jason Wang <jasowang@...hat.com> wrote:
>
> 在 2022/4/6 上午11:43, Xuan Zhuo 写道:
> > Separate the logic of attach vring, subsequent patches will call it
> > separately.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > ---
> >   drivers/virtio/virtio_ring.c | 20 ++++++++++++++------
> >   1 file changed, 14 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 6de67439cb57..083f2992ba0d 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -916,6 +916,19 @@ static void *virtqueue_detach_unused_buf_split(struct virtqueue *_vq)
> >   	return NULL;
> >   }
> >
> > +static void vring_virtqueue_attach_split(struct vring_virtqueue *vq,
> > +					 struct vring vring,
> > +					 struct vring_desc_state_split *desc_state,
> > +					 struct vring_desc_extra *desc_extra)
> > +{
> > +	vq->split.vring = vring;
> > +	vq->split.queue_dma_addr = 0;
> > +	vq->split.queue_size_in_bytes = 0;
>
>
> Any reason to add the above two assignment in attach? It seems belong to
> free or reset.

As discussed in patch 11, since there is no dma_addr in __vring_new_virtqueue(),
the corresponding vq->split.queue_dma_addr cannot be set, so the purpose here
is just to initialize it.

In the next version, struct vring_virtqueue_split will be passed to
vring_virtqueue_attach_split() to make the logic here look more reasonable.

Thanks.


>
> Thanks
>
>
> > +
> > +	vq->split.desc_state = desc_state;
> > +	vq->split.desc_extra = desc_extra;
> > +}
> > +
> >   static int vring_alloc_state_extra_split(u32 num,
> >   					 struct vring_desc_state_split **desc_state,
> >   					 struct vring_desc_extra **desc_extra)
> > @@ -2262,10 +2275,6 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
> >   	if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
> >   		vq->weak_barriers = false;
> >
> > -	vq->split.queue_dma_addr = 0;
> > -	vq->split.queue_size_in_bytes = 0;
> > -
> > -	vq->split.vring = vring;
> >   	vq->split.avail_flags_shadow = 0;
> >   	vq->split.avail_idx_shadow = 0;
> >
> > @@ -2283,8 +2292,7 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
> >   		return NULL;
> >   	}
> >
> > -	vq->split.desc_state = state;
> > -	vq->split.desc_extra = extra;
> > +	vring_virtqueue_attach_split(vq, vring, state, extra);
> >
> >   	/* Put everything in free lists. */
> >   	vq->free_head = 0;
>