netdev - Re: [PATCH v11 14/40] virtio_ring: split: introduce virtqueue_resize

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Date:   Fri, 1 Jul 2022 17:09:13 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        virtualization@...ts.linux-foundation.org
Cc:     Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        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>,
        Eric Farman <farman@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...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>,
        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,
        kangjie.xu@...ux.alibaba.com
Subject: Re: [PATCH v11 14/40] virtio_ring: split: introduce
 virtqueue_resize_split()


在 2022/6/29 14:56, Xuan Zhuo 写道:
> virtio ring split supports resize.
>
> Only after the new vring is successfully allocated based on the new num,
> we will release the old vring. In any case, an error is returned,
> indicating that the vring still points to the old vring.
>
> In the case of an error, re-initialize(virtqueue_reinit_split()) the
> virtqueue to ensure that the vring can be used.
>
> In addition, vring_align, may_reduce_num are necessary for reallocating
> vring, so they are retained for creating vq.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>   drivers/virtio/virtio_ring.c | 32 ++++++++++++++++++++++++++++++++
>   1 file changed, 32 insertions(+)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 9c83c5e6d5a9..1aaa1e5f9991 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -212,6 +212,7 @@ struct vring_virtqueue {
>   };
>   
>   static struct vring_desc_extra *vring_alloc_desc_extra(unsigned int num);
> +static void vring_free(struct virtqueue *_vq);
>   
>   /*
>    * Helpers.
> @@ -1114,6 +1115,37 @@ static struct virtqueue *vring_create_virtqueue_split(
>   	return vq;
>   }
>   
> +static int virtqueue_resize_split(struct virtqueue *_vq, u32 num)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	struct vring_virtqueue_split vring = {};
> +	struct virtio_device *vdev = _vq->vdev;
> +	int err;
> +
> +	err = vring_alloc_queue_split(&vring, vdev, num, vq->split.vring_align,
> +				      vq->split.may_reduce_num);
> +	if (err)
> +		goto err;


It's better to have decouple the allocation future more to avoid any 
rewind here in the future.

But the patch should be fine.

So

Acked-by: Jason Wang <jasowang@...hat.com>


> +
> +	err = vring_alloc_state_extra_split(&vring);
> +	if (err) {
> +		vring_free_split(&vring, vdev);
> +		goto err;
> +	}
> +
> +	vring_free(&vq->vq);
> +
> +	virtqueue_init(vq, vring.vring.num);
> +	virtqueue_vring_attach_split(vq, &vring);
> +	virtqueue_vring_init_split(vq);
> +
> +	return 0;
> +
> +err:
> +	virtqueue_reinit_split(vq);
> +	return -ENOMEM;
> +}
> +
>   
>   /*
>    * Packed ring specific functions - *_packed().