[PATCH v2 3/3] virtio_ring: Use const to annotate read-only pointer params

Feng Liu
Fri, 10 Mar 2023 05:34:28 -0000

Add const to make the read-only pointer parameters clear, similar to
many existing functions.

To implement this change, the commit also introduces the use of
`container_of_const` to implement `to_vvq`, which ensures the const-ness
of read-only parameters and avoids accidental modification of their
members.

Signed-off-by: Feng Liu <feliu at nvidia.com>
Reviewed-by: Jiri Pirko <jiri at nvidia.com>
Reviewed-by: Parav Pandit <parav at nvidia.com>
Reviewed-by: Gavin Li <gavinl at nvidia.com>
Reviewed-by: Bodong Wang <bodong at nvidia.com>

---
v1 -> v2
feedbacks from Michael S. Tsirkin
- use `container_of_const` to implement `to_vvq`
---
 drivers/virtio/virtio_ring.c | 36 ++++++++++++++++++------------------
 include/linux/virtio.h       | 14 +++++++-------
 2 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index a26fab91c59f..4c3bb0ddeb9b 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -231,9 +231,9 @@ static void vring_free(struct virtqueue *_vq);
  * Helpers.
  */

-#define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
+#define to_vvq(_vq) container_of_const(_vq, struct vring_virtqueue, vq)

-static bool virtqueue_use_indirect(struct vring_virtqueue *vq,
+static bool virtqueue_use_indirect(const struct vring_virtqueue *vq,
 				   unsigned int total_sg)
 {
 	/*
@@ -269,7 +269,7 @@ static bool virtqueue_use_indirect(struct vring_virtqueue
*vq,
  * unconditionally on data path.
  */

-static bool vring_use_dma_api(struct virtio_device *vdev)
+static bool vring_use_dma_api(const struct virtio_device *vdev)
 {
 	if (!virtio_has_dma_quirk(vdev))
 		return true;
@@ -289,7 +289,7 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
 	return false;
 }

-size_t virtio_max_dma_size(struct virtio_device *vdev)
+size_t virtio_max_dma_size(const struct virtio_device *vdev)
 {
 	size_t max_segment_size = SIZE_MAX;

@@ -423,7 +423,7 @@ static void virtqueue_init(struct vring_virtqueue *vq, u32
num)
  */

 static void vring_unmap_one_split_indirect(const struct vring_virtqueue *vq,
-					   struct vring_desc *desc)
+					   const struct vring_desc *desc)
 {
 	u16 flags;

@@ -1183,7 +1183,7 @@ static u16 packed_last_used(u16 last_used_idx)
 }

 static void vring_unmap_extra_packed(const struct vring_virtqueue *vq,
-				     struct vring_desc_extra *extra)
+				     const struct vring_desc_extra *extra)
 {
 	u16 flags;

@@ -1206,7 +1206,7 @@ static void vring_unmap_extra_packed(const struct
vring_virtqueue *vq,
 }

 static void vring_unmap_desc_packed(const struct vring_virtqueue *vq,
-				   struct vring_packed_desc *desc)
+				    const struct vring_packed_desc *desc)
 {
 	u16 flags;

@@ -2786,10 +2786,10 @@ EXPORT_SYMBOL_GPL(vring_transport_features);
  * Returns the size of the vring.  This is mainly used for boasting to
  * userspace.  Unlike other operations, this need not be serialized.
  */
-unsigned int virtqueue_get_vring_size(struct virtqueue *_vq)
+unsigned int virtqueue_get_vring_size(const struct virtqueue *_vq)
 {

-	struct vring_virtqueue *vq = to_vvq(_vq);
+	const struct vring_virtqueue *vq = to_vvq(_vq);

 	return vq->packed_ring ? vq->packed.vring.num : vq->split.vring.num;
 }
@@ -2819,9 +2819,9 @@ void __virtqueue_unbreak(struct virtqueue *_vq)
 }
 EXPORT_SYMBOL_GPL(__virtqueue_unbreak);

-bool virtqueue_is_broken(struct virtqueue *_vq)
+bool virtqueue_is_broken(const struct virtqueue *_vq)
 {
-	struct vring_virtqueue *vq = to_vvq(_vq);
+	const struct vring_virtqueue *vq = to_vvq(_vq);

 	return READ_ONCE(vq->broken);
 }
@@ -2868,9 +2868,9 @@ void __virtio_unbreak_device(struct virtio_device *dev)
 }
 EXPORT_SYMBOL_GPL(__virtio_unbreak_device);

-dma_addr_t virtqueue_get_desc_addr(struct virtqueue *_vq)
+dma_addr_t virtqueue_get_desc_addr(const struct virtqueue *_vq)
 {
-	struct vring_virtqueue *vq = to_vvq(_vq);
+	const struct vring_virtqueue *vq = to_vvq(_vq);

 	BUG_ON(!vq->we_own_ring);

@@ -2881,9 +2881,9 @@ dma_addr_t virtqueue_get_desc_addr(struct virtqueue *_vq)
 }
 EXPORT_SYMBOL_GPL(virtqueue_get_desc_addr);

-dma_addr_t virtqueue_get_avail_addr(struct virtqueue *_vq)
+dma_addr_t virtqueue_get_avail_addr(const struct virtqueue *_vq)
 {
-	struct vring_virtqueue *vq = to_vvq(_vq);
+	const struct vring_virtqueue *vq = to_vvq(_vq);

 	BUG_ON(!vq->we_own_ring);

@@ -2895,9 +2895,9 @@ dma_addr_t virtqueue_get_avail_addr(struct virtqueue *_vq)
 }
 EXPORT_SYMBOL_GPL(virtqueue_get_avail_addr);

-dma_addr_t virtqueue_get_used_addr(struct virtqueue *_vq)
+dma_addr_t virtqueue_get_used_addr(const struct virtqueue *_vq)
 {
-	struct vring_virtqueue *vq = to_vvq(_vq);
+	const struct vring_virtqueue *vq = to_vvq(_vq);

 	BUG_ON(!vq->we_own_ring);

@@ -2910,7 +2910,7 @@ dma_addr_t virtqueue_get_used_addr(struct virtqueue *_vq)
 EXPORT_SYMBOL_GPL(virtqueue_get_used_addr);

 /* Only available for split ring */
-const struct vring *virtqueue_get_vring(struct virtqueue *vq)
+const struct vring *virtqueue_get_vring(const struct virtqueue *vq)
 {
 	return &to_vvq(vq)->split.vring;
 }
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 2b472514c49b..c4225653f949 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -84,14 +84,14 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *vq);

 void *virtqueue_detach_unused_buf(struct virtqueue *vq);

-unsigned int virtqueue_get_vring_size(struct virtqueue *vq);
+unsigned int virtqueue_get_vring_size(const struct virtqueue *vq);

-bool virtqueue_is_broken(struct virtqueue *vq);
+bool virtqueue_is_broken(const struct virtqueue *vq);

-const struct vring *virtqueue_get_vring(struct virtqueue *vq);
-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);
+const struct vring *virtqueue_get_vring(const struct virtqueue *vq);
+dma_addr_t virtqueue_get_desc_addr(const struct virtqueue *vq);
+dma_addr_t virtqueue_get_avail_addr(const struct virtqueue *vq);
+dma_addr_t virtqueue_get_used_addr(const struct virtqueue *vq);

 int virtqueue_resize(struct virtqueue *vq, u32 num,
 		     void (*recycle)(struct virtqueue *vq, void *buf));
@@ -147,7 +147,7 @@ int virtio_device_restore(struct virtio_device *dev);
 #endif
 void virtio_reset_device(struct virtio_device *dev);

-size_t virtio_max_dma_size(struct virtio_device *vdev);
+size_t virtio_max_dma_size(const struct virtio_device *vdev);

 #define virtio_device_for_each_vq(vdev, vq) \
 	list_for_each_entry(vq, &vdev->vqs, list)
--
2.34.1