vkr: add support for larger rings

Now that vkr_ring supports iov, we can allow larger rings.  This also
adjusts VKR_RING_BUFFER_MAX_SIZE to be realistic.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Ryan Neph <ryanneph@google.com>
Reviewed-by: Yiwei Zhang <zzyiwei@chromium.org>

src/venus/vkr_ring.h

@@ -8,8 +8,14 @@
 
 #include "vkr_common.h"
 
-/* this must not exceed UINT32_MAX because the ring head and tail are 32-bit */
-#define VKR_RING_BUFFER_MAX_SIZE UINT32_MAX
+/* We read from the ring buffer to a temporary buffer for
+ * virgl_context::submit_cmd.  Until that is changed, we want to put a limit
+ * on the size of the temporary buffer.  It also makes no sense to have huge
+ * rings.
+ *
+ * This must not exceed UINT32_MAX because the ring head and tail are 32-bit.
+ */
+#define VKR_RING_BUFFER_MAX_SIZE (16u * 1024 * 1024)
 
 /* The layout of a ring in a virgl_resource.  This is parsed and discarded by
  * vkr_ring_create.

src/venus/vkr_transport.c

@@ -177,12 +177,8 @@ vkr_ring_layout_init(struct vkr_ring_layout *layout,
    };
    /* clang-format on */
 
-   if (res->iov_count != 1) {
-      vkr_log("no scatter-gather support for ring buffers (TODO)");
-      return false;
-   }
-
-   const struct vkr_region res_size = VKR_REGION_INIT(0, res->iov[0].iov_len);
+   const struct vkr_region res_size =
+      VKR_REGION_INIT(0, vrend_get_iovec_size(res->iov, res->iov_count));
    if (!vkr_region_is_valid(&res_region) || !vkr_region_is_within(&res_region, &res_size))
       return false;