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

Agree for all.

Thanks.

On Wed, 9 Mar 2022 14:46:01 +0800, Jason Wang [off-list ref] wrote:

在 2022/3/8 下午8:34, Xuan Zhuo 写道:

quoted

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.

quoted

+
  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.

quoted

  {
-	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:

quoted

+
+	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

quoted

-	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;

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