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

[Jason Wang]

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 <xuanz...@linux.alibaba.com>
---
  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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