[RFC v4 3/5] vhost: Data structure changes to support packed vqs

[Sahil Siddiq]

Introduce "struct vring_packed".

Modify VhostShadowVirtqueue so it can support split
and packed virtqueue formats.

Signed-off-by: Sahil Siddiq <sahilcdq@proton.me>
---
Changes v3 -> v4:
- Commit #2 of v3 is now commit #3 in this series.
- vhost-shadow-virtqueue.h
  (struct VhostShadowVirtqueue): Add bool is_packed.
  This was initially in commit #3 of v3.

 hw/virtio/vhost-shadow-virtqueue.h | 69 ++++++++++++++++++++----------
 1 file changed, 47 insertions(+), 22 deletions(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.h 
b/hw/virtio/vhost-shadow-virtqueue.h
index 19c842a15b..ce89bafedc 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -46,10 +46,56 @@ typedef struct VhostShadowVirtqueueOps {
     VirtQueueAvailCallback avail_handler;
 } VhostShadowVirtqueueOps;
 
+struct vring_packed {
+    /* Actual memory layout for this queue. */
+    struct {
+        unsigned int num;
+        struct vring_packed_desc *desc;
+        struct vring_packed_desc_event *driver;
+        struct vring_packed_desc_event *device;
+    } vring;
+
+    /* Avail used flags. */
+    uint16_t avail_used_flags;
+
+    /* Index of the next avail descriptor. */
+    uint16_t next_avail_idx;
+
+    /* Driver ring wrap counter */
+    bool avail_wrap_counter;
+};
+
 /* Shadow virtqueue to relay notifications */
 typedef struct VhostShadowVirtqueue {
+    /* True if packed virtqueue */
+    bool is_packed;
+
+    /* Virtio queue shadowing */
+    VirtQueue *vq;
+
+    /* Virtio device */
+    VirtIODevice *vdev;
+
+    /* SVQ vring descriptors state */
+    SVQDescState *desc_state;
+
+    /*
+     * Backup next field for each descriptor so we can recover securely, not
+     * needing to trust the device access.
+     */
+    uint16_t *desc_next;
+
+    /* Next free descriptor */
+    uint16_t free_head;
+
+    /* Size of SVQ vring free descriptors */
+    uint16_t num_free;
+
     /* Shadow vring */
-    struct vring vring;
+    union {
+        struct vring vring;
+        struct vring_packed vring_packed;
+    };
 
     /* Shadow kick notifier, sent to vhost */
     EventNotifier hdev_kick;
@@ -69,27 +115,12 @@ typedef struct VhostShadowVirtqueue {
     /* Guest's call notifier, where the SVQ calls guest. */
     EventNotifier svq_call;
 
-    /* Virtio queue shadowing */
-    VirtQueue *vq;
-
-    /* Virtio device */
-    VirtIODevice *vdev;
-
     /* IOVA mapping */
     VhostIOVATree *iova_tree;
 
-    /* SVQ vring descriptors state */
-    SVQDescState *desc_state;
-
     /* Next VirtQueue element that guest made available */
     VirtQueueElement *next_guest_avail_elem;
 
-    /*
-     * Backup next field for each descriptor so we can recover securely, not
-     * needing to trust the device access.
-     */
-    uint16_t *desc_next;
-
     /* Caller callbacks */
     const VhostShadowVirtqueueOps *ops;
 
@@ -99,17 +130,11 @@ typedef struct VhostShadowVirtqueue {
     /* Next head to expose to the device */
     uint16_t shadow_avail_idx;
 
-    /* Next free descriptor */
-    uint16_t free_head;
-
     /* Last seen used idx */
     uint16_t shadow_used_idx;
 
     /* Next head to consume from the device */
     uint16_t last_used_idx;
-
-    /* Size of SVQ vring free descriptors */
-    uint16_t num_free;
 } VhostShadowVirtqueue;
 
 bool vhost_svq_valid_features(uint64_t features, Error **errp);
-- 
2.47.0