virtio-gpu: add the ability to export resources

Fixes: #76
Signed-off-by: David Stevens <stevensd@chromium.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

virtio-gpu.tex

@@ -35,6 +35,8 @@ \subsection{Feature bits}\label{sec:Device Types / GPU Device / Feature bits}
 \begin{description}
 \item[VIRTIO_GPU_F_VIRGL (0)] virgl 3D mode is supported.
 \item[VIRTIO_GPU_F_EDID  (1)] EDID is supported.
+\item[VIRTIO_GPU_F_RESOURCE_UUID (2)] assigning resources UUIDs for export
+  to other virtio devices is supported.
 \end{description}
 
 \subsection{Device configuration layout}\label{sec:Device Types / GPU Device / Device configuration layout}
@@ -186,6 +188,7 @@ \subsubsection{Device Operation: Request header}\label{sec:Device Types / GPU De
         VIRTIO_GPU_CMD_GET_CAPSET_INFO,
         VIRTIO_GPU_CMD_GET_CAPSET,
         VIRTIO_GPU_CMD_GET_EDID,
+        VIRTIO_GPU_CMD_RESOURCE_ASSIGN_UUID,
 
         /* 3d commands (OpenGL) */
         VIRTIO_GPU_CMD_CTX_CREATE = 0x0200,
@@ -207,6 +210,7 @@ \subsubsection{Device Operation: Request header}\label{sec:Device Types / GPU De
         VIRTIO_GPU_RESP_OK_CAPSET_INFO,
         VIRTIO_GPU_RESP_OK_CAPSET,
         VIRTIO_GPU_RESP_OK_EDID,
+        VIRTIO_GPU_RESP_OK_RESOURCE_UUID,
 
         /* error responses */
         VIRTIO_GPU_RESP_ERR_UNSPEC = 0x1200,
@@ -469,6 +473,32 @@ \subsubsection{Device Operation: controlq}\label{sec:Device Types / GPU Device /
 This detaches any backing pages from a resource, to be used in case of
 guest swapping or object destruction.
 
+\item[VIRTIO_GPU_CMD_RESOURCE_ASSIGN_UUID] Creates an exported object from
+  a resource. Request data is \field{struct
+    virtio_gpu_resource_assign_uuid}.  Response type is
+  VIRTIO_GPU_RESP_OK_RESOURCE_UUID, response data is \field{struct
+    virtio_gpu_resp_resource_uuid}. Support is optional and negotiated
+    using the VIRTIO_GPU_F_RESOURCE_UUID feature flag.
+
+\begin{lstlisting}
+struct virtio_gpu_resource_assign_uuid {
+        struct virtio_gpu_ctrl_hdr hdr;
+        le32 resource_id;
+        le32 padding;
+};
+
+struct virtio_gpu_resp_resource_uuid {
+        struct virtio_gpu_ctrl_hdr hdr;
+        u8 uuid[16];
+};
+\end{lstlisting}
+
+The response contains a UUID which identifies the exported object created from
+the host private resource. Note that if the resource has an attached backing,
+modifications made to the host private resource through the exported object by
+other devices are not visible in the attached backing until they are transferred
+into the backing.
+
 \end{description}
 
 \subsubsection{Device Operation: controlq (3d)}\label{sec:Device Types / GPU Device / Device Operation / Device Operation: controlq (3d)}