Re: [PATCH v7 04/26] virtio_ring: split: extract the logic of creating vring

From: Jason Wang <jasowang@redhat.com>
To: Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
	virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org
Cc: Jeff Dike <jdike@addtoit.com>,
	Richard Weinberger <richard@nod.at>,
	Anton Ivanov <anton.ivanov@cambridgegreys.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Hans de Goede <hdegoede@redhat.com>,
	Mark Gross <markgross@kernel.org>,
	Vadim Pasternak <vadimp@nvidia.com>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Mathieu Poirier <mathieu.poirier@linaro.org>,
	Cornelia Huck <cohuck@redhat.com>,
	Halil Pasic <pasic@linux.ibm.com>,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Christian Borntraeger <borntraeger@linux.ibm.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	Sven Schnelle <svens@linux.ibm.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	John Fastabend <john.fastabend@gmail.com>,
	Johannes Berg <johannes.berg@intel.com>,
	Vincent Whitchurch <vincent.whitchurch@axis.com>,
	linux-um@lists.infradead.org,
	platform-driver-x86@vger.kernel.org,
	linux-remoteproc@vger.kernel.org, linux-s390@vger.kernel.org,
	kvm@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH v7 04/26] virtio_ring: split: extract the logic of creating vring
Date: Wed, 9 Mar 2022 14:46:01 +0800	[thread overview]
Message-ID: <4b32d0b4-b794-cc1c-25f7-50b5ea6ac25e@redhat.com> (raw)
In-Reply-To: <20220308123518.33800-5-xuanzhuo@linux.alibaba.com>

在 2022/3/8 下午8:34, Xuan Zhuo 写道:
> Separate the logic of split to create vring queue.
>
> For the convenience of passing parameters, add a structure
> vring_split.
>
> This feature is required for subsequent virtuqueue reset vring.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
>   drivers/virtio/virtio_ring.c | 74 +++++++++++++++++++++++++-----------
>   1 file changed, 51 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index b87130c8f312..d32793615451 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -85,6 +85,13 @@ struct vring_desc_extra {
>   	u16 next;			/* The next desc state in a list. */
>   };
>   
> +struct vring_split {
> +	void *queue;
> +	dma_addr_t dma_addr;
> +	size_t queue_size_in_bytes;
> +	struct vring vring;
> +};

So this structure will be only used in vring_create_vring_split() which 
seems not that useful.

More see below.

> +
>   struct vring_virtqueue {
>   	struct virtqueue vq;
>   
> @@ -915,28 +922,21 @@ static void *virtqueue_detach_unused_buf_split(struct virtqueue *_vq)
>   	return NULL;
>   }
>   
> -static struct virtqueue *vring_create_virtqueue_split(
> -	unsigned int index,
> -	unsigned int num,
> -	unsigned int vring_align,
> -	struct virtio_device *vdev,
> -	bool weak_barriers,
> -	bool may_reduce_num,
> -	bool context,
> -	bool (*notify)(struct virtqueue *),
> -	void (*callback)(struct virtqueue *),
> -	const char *name)
> +static int vring_create_vring_split(struct vring_split *vring,
> +				    struct virtio_device *vdev,
> +				    unsigned int vring_align,
> +				    bool weak_barriers,
> +				    bool may_reduce_num,
> +				    u32 num)

I'd rename this as vring_alloc_queue_split() and let it simply return 
the address of queue like vring_alloc_queue().

And let it simple accept dma_addr_t *dma_adder instead of vring_split.

>   {
> -	struct virtqueue *vq;
>   	void *queue = NULL;
>   	dma_addr_t dma_addr;
>   	size_t queue_size_in_bytes;
> -	struct vring vring;
>   
>   	/* We assume num is a power of 2. */
>   	if (num & (num - 1)) {
>   		dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
> -		return NULL;
> +		return -EINVAL;
>   	}
>   
>   	/* TODO: allocate each queue chunk individually */
> @@ -947,11 +947,11 @@ static struct virtqueue *vring_create_virtqueue_split(
>   		if (queue)
>   			break;
>   		if (!may_reduce_num)
> -			return NULL;
> +			return -ENOMEM;
>   	}
>   
>   	if (!num)
> -		return NULL;
> +		return -ENOMEM;
>   
>   	if (!queue) {
>   		/* Try to get a single page. You are my only hope! */
> @@ -959,21 +959,49 @@ static struct virtqueue *vring_create_virtqueue_split(
>   					  &dma_addr, GFP_KERNEL|__GFP_ZERO);
>   	}
>   	if (!queue)
> -		return NULL;
> +		return -ENOMEM;
>   
>   	queue_size_in_bytes = vring_size(num, vring_align);
> -	vring_init(&vring, num, queue, vring_align);
> +	vring_init(&vring->vring, num, queue, vring_align);

It's better to move this to its caller (vring_create_virtqueue_split), 
so we have rather simple logic below:

> +
> +	vring->dma_addr = dma_addr;
> +	vring->queue = queue;
> +	vring->queue_size_in_bytes = queue_size_in_bytes;
> +
> +	return 0;
> +}
> +
> +static struct virtqueue *vring_create_virtqueue_split(
> +	unsigned int index,
> +	unsigned int num,
> +	unsigned int vring_align,
> +	struct virtio_device *vdev,
> +	bool weak_barriers,
> +	bool may_reduce_num,
> +	bool context,
> +	bool (*notify)(struct virtqueue *),
> +	void (*callback)(struct virtqueue *),
> +	const char *name)
> +{
> +	struct vring_split vring;
> +	struct virtqueue *vq;
> +	int err;
> +
> +	err = vring_create_vring_split(&vring, vdev, vring_align, weak_barriers,
> +				       may_reduce_num, num);
> +	if (err)
> +		return NULL;

queue = vring_alloc_queue_split(vdev, &dma_addr, ...);

if (!queue)

     return -ENOMEM;

vring_init();

...

Thanks

>   
> -	vq = __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
> +	vq = __vring_new_virtqueue(index, vring.vring, vdev, weak_barriers, context,
>   				   notify, callback, name);
>   	if (!vq) {
> -		vring_free_queue(vdev, queue_size_in_bytes, queue,
> -				 dma_addr);
> +		vring_free_queue(vdev, vring.queue_size_in_bytes, vring.queue,
> +				 vring.dma_addr);
>   		return NULL;
>   	}
>   
> -	to_vvq(vq)->split.queue_dma_addr = dma_addr;
> -	to_vvq(vq)->split.queue_size_in_bytes = queue_size_in_bytes;
> +	to_vvq(vq)->split.queue_dma_addr = vring.dma_addr;
> +	to_vvq(vq)->split.queue_size_in_bytes = vring.queue_size_in_bytes;
>   	to_vvq(vq)->we_own_ring = true;
>   
>   	return vq;