[PATCH v9 18/32] virtio_ring: introduce virtqueue_resize()

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

Introduce virtqueue_resize() to implement the resize of vring.
Based on these, the driver can dynamically adjust the size of the vring.
For example: ethtool -G.

virtqueue_resize() implements resize based on the vq reset function. In
case of failure to allocate a new vring, it will give up resize and use
the original vring.

During this process, if the re-enable reset vq fails, the vq can no
longer be used. Although the probability of this situation is not high.

The parameter recycle is used to recycle the buffer that is no longer
used.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
 drivers/virtio/virtio_ring.c | 69 ++++++++++++++++++++++++++++++++++++
 include/linux/virtio.h       |  3 ++
 2 files changed, 72 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 06f66b15c86c..6250e19fc5bf 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -2554,6 +2554,75 @@ struct virtqueue *vring_create_virtqueue(
 }
 EXPORT_SYMBOL_GPL(vring_create_virtqueue);
 
+/**
+ * virtqueue_resize - resize the vring of vq
+ * @_vq: the struct virtqueue we're talking about.
+ * @num: new ring num
+ * @recycle: callback for recycle the useless buffer
+ *
+ * When it is really necessary to create a new vring, it will set the current vq
+ * into the reset state. Then call the passed callback to recycle the buffer
+ * that is no longer used. Only after the new vring is successfully created, the
+ * old vring will be released.
+ *
+ * Caller must ensure we don't call this with other virtqueue operations
+ * at the same time (except where noted).
+ *
+ * Returns zero or a negative error.
+ */
+int virtqueue_resize(struct virtqueue *_vq, u32 num,
+		     void (*recycle)(struct virtqueue *vq, void *buf))
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	struct virtio_device *vdev = vq->vq.vdev;
+	bool packed;
+	void *buf;
+	int err;
+
+	if (!vq->we_own_ring)
+		return -EINVAL;
+
+	if (num > vq->vq.num_max)
+		return -E2BIG;
+
+	if (!num)
+		return -EINVAL;
+
+	packed = virtio_has_feature(vdev, VIRTIO_F_RING_PACKED) ? true : false;
+
+	if ((packed ? vq->packed.vring.num : vq->split.vring.num) == num)
+		return 0;
+
+	if (!vdev->config->reset_vq)
+		return -ENOENT;
+
+	if (!vdev->config->enable_reset_vq)
+		return -ENOENT;
+
+	err = vdev->config->reset_vq(_vq);
+	if (err)
+		return err;
+
+	while ((buf = virtqueue_detach_unused_buf(_vq)) != NULL)
+		recycle(_vq, buf);
+
+	if (packed) {
+		err = virtqueue_resize_packed(_vq, num);
+		if (err)
+			virtqueue_reinit_packed(vq);
+	} else {
+		err = virtqueue_resize_split(_vq, num);
+		if (err)
+			virtqueue_reinit_split(vq);
+	}
+
+	if (vdev->config->enable_reset_vq(_vq))
+		return -EBUSY;
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(virtqueue_resize);
+
 /* Only available for split ring */
 struct virtqueue *vring_new_virtqueue(unsigned int index,
 				      unsigned int num,
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index d59adc4be068..c86ff02e0ca0 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -91,6 +91,9 @@ dma_addr_t virtqueue_get_desc_addr(struct virtqueue *vq);
 dma_addr_t virtqueue_get_avail_addr(struct virtqueue *vq);
 dma_addr_t virtqueue_get_used_addr(struct virtqueue *vq);
 
+int virtqueue_resize(struct virtqueue *vq, u32 num,
+		     void (*recycle)(struct virtqueue *vq, void *buf));
+
 /**
  * virtio_device - representation of a device using virtio
  * @index: unique position on the virtio bus
-- 
2.31.0