[RFC PATCH 06/12] vhost: Use opaque data in SVQDescState

[Eugenio Pérez]

Since we'll allow net/vhost-vdpa to add elements that don't come from
the guest, we need to store opaque data that makes sense to the caller.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.h |  4 ++--
 hw/virtio/vhost-shadow-virtqueue.c | 20 +++++++++++---------
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.h 
b/hw/virtio/vhost-shadow-virtqueue.h
index d04c34a589..03eb7ff670 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -16,7 +16,7 @@
 #include "hw/virtio/vhost-iova-tree.h"
 
 typedef struct SVQDescState {
-    VirtQueueElement *elem;
+    void *data;
 
     /*
      * Number of descriptors exposed to the device. May or may not match
@@ -115,7 +115,7 @@ void vhost_svq_push_elem(VhostShadowVirtqueue *svq,
                          const VirtQueueElement *elem, uint32_t len);
 int vhost_svq_add(VhostShadowVirtqueue *svq, const struct iovec *out_sg,
                   size_t out_num, const struct iovec *in_sg, size_t in_num,
-                  VirtQueueElement *elem);
+                  void *data);
 size_t vhost_svq_poll(VhostShadowVirtqueue *svq);
 
 void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd);
diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
b/hw/virtio/vhost-shadow-virtqueue.c
index 29633b7a29..88e290d94b 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -237,7 +237,7 @@ static void vhost_svq_kick(VhostShadowVirtqueue *svq)
  */
 int vhost_svq_add(VhostShadowVirtqueue *svq, const struct iovec *out_sg,
                   size_t out_num, const struct iovec *in_sg, size_t in_num,
-                  VirtQueueElement *elem)
+                  void *data)
 {
     unsigned qemu_head;
     unsigned ndescs = in_num + out_num;
@@ -252,7 +252,7 @@ int vhost_svq_add(VhostShadowVirtqueue *svq, const struct 
iovec *out_sg,
         return -EINVAL;
     }
 
-    svq->desc_state[qemu_head].elem = elem;
+    svq->desc_state[qemu_head].data = data;
     svq->desc_state[qemu_head].ndescs = ndescs;
     vhost_svq_kick(svq);
     return 0;
@@ -389,8 +389,7 @@ static uint16_t vhost_svq_last_desc_of_chain(const 
VhostShadowVirtqueue *svq,
     return i;
 }
 
-static VirtQueueElement *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
-                                           uint32_t *len)
+static void *vhost_svq_get_buf(VhostShadowVirtqueue *svq, uint32_t *len)
 {
     const vring_used_t *used = svq->vring.used;
     vring_used_elem_t used_elem;
@@ -413,7 +412,7 @@ static VirtQueueElement 
*vhost_svq_get_buf(VhostShadowVirtqueue *svq,
         return NULL;
     }
 
-    if (unlikely(!svq->desc_state[used_elem.id].elem)) {
+    if (unlikely(!svq->desc_state[used_elem.id].data)) {
         qemu_log_mask(LOG_GUEST_ERROR,
             "Device %s says index %u is used, but it was not available",
             svq->vdev->name, used_elem.id);
@@ -426,7 +425,7 @@ static VirtQueueElement 
*vhost_svq_get_buf(VhostShadowVirtqueue *svq,
     svq->free_head = used_elem.id;
 
     *len = used_elem.len;
-    return g_steal_pointer(&svq->desc_state[used_elem.id].elem);
+    return g_steal_pointer(&svq->desc_state[used_elem.id].data);
 }
 
 /**
@@ -498,8 +497,7 @@ size_t vhost_svq_poll(VhostShadowVirtqueue *svq)
 {
     do {
         uint32_t len;
-        VirtQueueElement *elem = vhost_svq_get_buf(svq, &len);
-        if (elem) {
+        if (vhost_svq_get_buf(svq, &len)) {
             return len;
         }
 
@@ -658,8 +656,12 @@ void vhost_svq_stop(VhostShadowVirtqueue *svq)
     vhost_svq_flush(svq, false);
 
     for (unsigned i = 0; i < svq->vring.num; ++i) {
+        /*
+         * We know .data is an element because external callers of
+         * vhost_svq_add use active polling, not SVQ
+         */
         g_autofree VirtQueueElement *elem = NULL;
-        elem = g_steal_pointer(&svq->desc_state[i].elem);
+        elem = g_steal_pointer(&svq->desc_state[i].data);
         if (elem) {
             virtqueue_detach_element(svq->vq, elem, 0);
         }
-- 
2.31.1