Re: [PATCH v12 08/40] virtio_ring: split: extract the logic of alloc queue

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在 2022/7/20 11:04, Xuan Zhuo 写道:
Separate the logic of split to create vring queue.

This feature is required for subsequent virtuqueue reset vring.

Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
  drivers/virtio/virtio_ring.c | 68 ++++++++++++++++++++++--------------
  1 file changed, 42 insertions(+), 26 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index c94c5461e702..c7971438bb2c 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -950,28 +950,19 @@ static void vring_free_split(struct vring_virtqueue_split *vring_split,
  	kfree(vring_split->desc_extra);
  }
-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_alloc_queue_split(struct vring_virtqueue_split *vring_split,
+				   struct virtio_device *vdev,
+				   u32 num,
+				   unsigned int vring_align,
+				   bool may_reduce_num)
  {
-	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 */
@@ -982,11 +973,11 @@ 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! */
@@ -994,21 +985,46 @@ static struct virtqueue *vring_create_virtqueue_split(
  					  &dma_addr, GFP_KERNEL|__GFP_ZERO);
  	}
  	if (!queue)
-		return NULL;
+		return -ENOMEM;
+
+	vring_init(&vring_split->vring, num, queue, vring_align);
- queue_size_in_bytes = vring_size(num, vring_align);
-	vring_init(&vring, num, queue, vring_align);
+	vring_split->queue_dma_addr = dma_addr;
+	vring_split->queue_size_in_bytes = vring_size(num, vring_align);
+
+	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_virtqueue_split vring_split = {};
+	struct virtqueue *vq;
+	int err;
+
+	err = vring_alloc_queue_split(&vring_split, vdev, num, vring_align,
+				      may_reduce_num);
+	if (err)
+		return NULL;
- vq = __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
-				   notify, callback, name);
+	vq = __vring_new_virtqueue(index, vring_split.vring, vdev, weak_barriers,
+				   context, notify, callback, name);
  	if (!vq) {
-		vring_free_queue(vdev, queue_size_in_bytes, queue,
-				 dma_addr);
+		vring_free_split(&vring_split, vdev);
  		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_split.queue_dma_addr;
+	to_vvq(vq)->split.queue_size_in_bytes = vring_split.queue_size_in_bytes;


This still seems a little bit redundant since the current logic is a little bit complicated since the vq->split is not initialized in a single place.

I wonder if it's better to:

vring_alloc_queue_split()
vring_alloc_desc_extra() (reorder to make patch 9 come first)

then we can simply assign vring_split to vq->split in __vring_new_virtqueue() since it has:

    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;

This seems to simplify the logic and task of e.g virtqueue_vring_attach_split() to a simple:

vq->split= vring_split;

And if this makes sense, we can do something similar to packed ring.

Thanks


  	to_vvq(vq)->we_own_ring = true;
return vq;




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