linux-kernel - [RFC PATCH 03/16] virtio_ring: split: extract virtqueue_update

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Date:   Sun, 24 Apr 2022 10:40:31 +0800
From:   Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To:     linux-kernel@...r.kernel.org
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: [RFC PATCH 03/16] virtio_ring: split: extract virtqueue_update_split()

Separate the logic for updating the vq state from virtqueue_add_split().

In this way, when the subsequent patch implements the logic of reusing
the buffer when resize, we can share this function.

Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
---
 drivers/virtio/virtio_ring.c | 95 ++++++++++++++++++++----------------
 1 file changed, 54 insertions(+), 41 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index f3ad9322b512..6fd45c9a3517 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -507,6 +507,51 @@ static inline unsigned int virtqueue_add_desc_split(struct virtqueue *vq,
 	return next;
 }
 
+static inline void virtqueue_update_split(struct vring_virtqueue *vq,
+					  u32 descs_used,
+					  u32 next,
+					  struct vring_desc *desc,
+					  void *data)
+{
+	struct virtqueue *_vq = &vq->vq;
+	u32 avail, head;
+
+	head = vq->free_head;
+
+	/* We're using some buffers from the free list. */
+	vq->vq.num_free -= descs_used;
+
+	/* Update free pointer */
+	vq->free_head = next;
+
+	/* Store token and indirect buffer state. */
+	vq->split.desc_state[head].data = data;
+	vq->split.desc_state[head].indir_desc = desc;
+
+	/* Put entry in available array (but don't update avail->idx until they
+	 * do sync).
+	 */
+	avail = vq->split.avail_idx_shadow & (vq->split.vring.num - 1);
+	vq->split.vring.avail->ring[avail] = cpu_to_virtio16(_vq->vdev, head);
+
+	/* Descriptors and available array need to be set before we expose the
+	 * new available array entries.
+	 */
+	virtio_wmb(vq->weak_barriers);
+	vq->split.avail_idx_shadow++;
+	vq->split.vring.avail->idx = cpu_to_virtio16(_vq->vdev,
+						vq->split.avail_idx_shadow);
+	vq->num_added++;
+
+	pr_debug("Added buffer head %i to %p\n", head, vq);
+
+	/* This is very unlikely, but theoretically possible.  Kick
+	 * just in case.
+	 */
+	if (unlikely(vq->num_added == (1 << 16) - 1))
+		virtqueue_kick(_vq);
+}
+
 static inline int virtqueue_add_split(struct virtqueue *_vq,
 				      struct scatterlist *sgs[],
 				      unsigned int total_sg,
@@ -519,7 +564,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 	struct vring_virtqueue *vq = to_vvq(_vq);
 	struct scatterlist *sg;
 	struct vring_desc *desc;
-	unsigned int i, n, avail, descs_used, prev, err_idx;
+	unsigned int i, n, descs_used, prev, err_idx;
 	int head;
 	bool indirect;
 
@@ -619,50 +664,18 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 		if (vring_mapping_error(vq, addr))
 			goto unmap_release;
 
-		virtqueue_add_desc_split(_vq, vq->split.vring.desc,
-					 head, addr,
-					 total_sg * sizeof(struct vring_desc),
-					 VRING_DESC_F_INDIRECT,
-					 false);
+		i = virtqueue_add_desc_split(_vq, vq->split.vring.desc,
+					     head, addr,
+					     total_sg * sizeof(struct vring_desc),
+					     VRING_DESC_F_INDIRECT,
+					     false);
+	} else {
+		desc = ctx;
 	}
 
-	/* We're using some buffers from the free list. */
-	vq->vq.num_free -= descs_used;
-
-	/* Update free pointer */
-	if (indirect)
-		vq->free_head = vq->split.desc_extra[head].next;
-	else
-		vq->free_head = i;
-
-	/* Store token and indirect buffer state. */
-	vq->split.desc_state[head].data = data;
-	if (indirect)
-		vq->split.desc_state[head].indir_desc = desc;
-	else
-		vq->split.desc_state[head].indir_desc = ctx;
-
-	/* Put entry in available array (but don't update avail->idx until they
-	 * do sync). */
-	avail = vq->split.avail_idx_shadow & (vq->split.vring.num - 1);
-	vq->split.vring.avail->ring[avail] = cpu_to_virtio16(_vq->vdev, head);
-
-	/* Descriptors and available array need to be set before we expose the
-	 * new available array entries. */
-	virtio_wmb(vq->weak_barriers);
-	vq->split.avail_idx_shadow++;
-	vq->split.vring.avail->idx = cpu_to_virtio16(_vq->vdev,
-						vq->split.avail_idx_shadow);
-	vq->num_added++;
-
-	pr_debug("Added buffer head %i to %p\n", head, vq);
+	virtqueue_update_split(vq, descs_used, i, desc, data);
 	END_USE(vq);
 
-	/* This is very unlikely, but theoretically possible.  Kick
-	 * just in case. */
-	if (unlikely(vq->num_added == (1 << 16) - 1))
-		virtqueue_kick(_vq);
-
 	return 0;
 
 unmap_release:
-- 
2.31.0