[PATCH v2 09/19] vhost: Track number of descs in SVQElement

[Eugenio Pérez]

Since CVQ will be able to modify elements, the number of descriptors in
the guest may not match with the number of descriptors exposed. Track
separately.

Signed-off-by: Eugenio Pérez <epere...@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.h |  6 ++++++
 hw/virtio/vhost-shadow-virtqueue.c | 10 +++++-----
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.h 
b/hw/virtio/vhost-shadow-virtqueue.h
index f35d4b8f90..143c86a568 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -17,6 +17,12 @@
 
 typedef struct SVQElement {
     VirtQueueElement elem;
+
+    /*
+     * Number of descriptors exposed to the device. May or may not match
+     * guest's
+     */
+    unsigned int ndescs;
 } SVQElement;
 
 /* Shadow virtqueue to relay notifications */
diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
b/hw/virtio/vhost-shadow-virtqueue.c
index 442ca3cbd3..3b112c4ec8 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -243,10 +243,10 @@ static int vhost_svq_add(VhostShadowVirtqueue *svq, const 
struct iovec *out_sg,
                           size_t in_num, SVQElement *svq_elem)
 {
     unsigned qemu_head;
-    unsigned ndescs = in_num + out_num;
+    svq_elem->ndescs = in_num + out_num;
     bool ok;
 
-    if (unlikely(ndescs > vhost_svq_available_slots(svq))) {
+    if (unlikely(svq_elem->ndescs > vhost_svq_available_slots(svq))) {
         return -ENOSPC;
     }
 
@@ -393,7 +393,7 @@ static SVQElement *vhost_svq_get_buf(VhostShadowVirtqueue 
*svq,
     SVQElement *elem;
     const vring_used_t *used = svq->vring.used;
     vring_used_elem_t used_elem;
-    uint16_t last_used, last_used_chain, num;
+    uint16_t last_used, last_used_chain;
 
     if (!vhost_svq_more_used(svq)) {
         return NULL;
@@ -420,8 +420,8 @@ static SVQElement *vhost_svq_get_buf(VhostShadowVirtqueue 
*svq,
     }
 
     elem = svq->ring_id_maps[used_elem.id];
-    num = elem->elem.in_num + elem->elem.out_num;
-    last_used_chain = vhost_svq_last_desc_of_chain(svq, num, used_elem.id);
+    last_used_chain = vhost_svq_last_desc_of_chain(svq, elem->ndescs,
+                                                   used_elem.id);
     svq->desc_next[last_used_chain] = svq->free_head;
     svq->free_head = used_elem.id;
 
-- 
2.31.1