[RFC 3/4] virtio_ring: introduce virtqueue_detach_unused_buf_premapped

[Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>]

introduce virtqueue_detach_unused_buf_premapped() to collect the dma
info when get buf from virtio core for premapped mode.

If the virtio queue is premapped mode, the virtio-net send buf may
have many desc. Every desc dma address need to be unmap. So here we
introduce a new helper to collect the dma address of the buffer from
the virtio core.

Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
 drivers/virtio/virtio_ring.c | 33 +++++++++++++++++++++++++--------
 include/linux/virtio.h       |  1 +
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 18f021095afd..60666b31d437 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1001,7 +1001,7 @@ static bool virtqueue_enable_cb_delayed_split(struct virtqueue *_vq)
 	return true;
 }
 
-static void *virtqueue_detach_unused_buf_split(struct virtqueue *_vq)
+static void *virtqueue_detach_unused_buf_split(struct virtqueue *_vq, struct scatterlist *sg)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 	unsigned int i;
@@ -1014,7 +1014,7 @@ static void *virtqueue_detach_unused_buf_split(struct virtqueue *_vq)
 			continue;
 		/* detach_buf_split clears data, so grab it now. */
 		buf = vq->split.desc_state[i].data;
-		detach_buf_split(vq, i, NULL, NULL);
+		detach_buf_split(vq, i, sg, NULL);
 		vq->split.avail_idx_shadow--;
 		vq->split.vring.avail->idx = cpu_to_virtio16(_vq->vdev,
 				vq->split.avail_idx_shadow);
@@ -1908,7 +1908,7 @@ static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
 	return true;
 }
 
-static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
+static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq, struct scatterlist *sg)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 	unsigned int i;
@@ -1921,7 +1921,7 @@ static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
 			continue;
 		/* detach_buf clears data, so grab it now. */
 		buf = vq->packed.desc_state[i].data;
-		detach_buf_packed(vq, i, NULL, NULL);
+		detach_buf_packed(vq, i, sg, NULL);
 		END_USE(vq);
 		return buf;
 	}
@@ -2614,19 +2614,36 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
 EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
 
 /**
- * virtqueue_detach_unused_buf - detach first unused buffer
+ * virtqueue_detach_unused_buf_premapped - detach first unused buffer
  * @_vq: the struct virtqueue we're talking about.
+ * @sg: scatterlist array to store the dma info
+ *
+ * more see virtqueue_get_buf_ctx_dma()
  *
  * Returns NULL or the "data" token handed to virtqueue_add_*().
  * This is not valid on an active queue; it is useful for device
  * shutdown or the reset queue.
  */
-void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
+void *virtqueue_detach_unused_buf_premapped(struct virtqueue *_vq, struct scatterlist *sg)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
-	return vq->packed_ring ? virtqueue_detach_unused_buf_packed(_vq) :
-				 virtqueue_detach_unused_buf_split(_vq);
+	return vq->packed_ring ? virtqueue_detach_unused_buf_packed(_vq, sg) :
+				 virtqueue_detach_unused_buf_split(_vq, sg);
+}
+EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf_premapped);
+
+/**
+ * virtqueue_detach_unused_buf - detach first unused buffer
+ * @_vq: the struct virtqueue we're talking about.
+ *
+ * Returns NULL or the "data" token handed to virtqueue_add_*().
+ * This is not valid on an active queue; it is useful for device
+ * shutdown or the reset queue.
+ */
+void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
+{
+	return virtqueue_detach_unused_buf_premapped(_vq, NULL);
 }
 EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);
 
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 225271940223..7e9b0ea6b6b2 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -90,6 +90,7 @@ bool virtqueue_poll(struct virtqueue *vq, unsigned);
 bool virtqueue_enable_cb_delayed(struct virtqueue *vq);
 
 void *virtqueue_detach_unused_buf(struct virtqueue *vq);
+void *virtqueue_detach_unused_buf_premapped(struct virtqueue *_vq, struct scatterlist *sg);
 
 unsigned int virtqueue_get_vring_size(const struct virtqueue *vq);
 
-- 
2.32.0.3.g01195cf9f