See vhost-user.txt protocol documentation for details.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 contrib/libvhost-user/libvhost-user.h |  1 +
 include/hw/virtio/vhost-backend.h     |  1 +
 hw/virtio/vhost-user.c                | 15 +++++++++++++++
 docs/interop/vhost-user.txt           |  8 ++++++++
 4 files changed, 25 insertions(+)

diff --git a/contrib/libvhost-user/libvhost-user.h b/contrib/libvhost-user/libvhost-user.h
index 42e227cce6..9f30e05bd1 100644
--- a/contrib/libvhost-user/libvhost-user.h
+++ b/contrib/libvhost-user/libvhost-user.h
@@ -93,6 +93,7 @@ typedef enum VhostUserRequest {
     VHOST_USER_POSTCOPY_END     = 30,
     VHOST_USER_INPUT_GET_CONFIG = 31,
     VHOST_USER_GPU_SET_SOCKET   = 32,
+    VHOST_USER_GPU_GET_NUM_CAPSETS = 33,
     VHOST_USER_MAX
 } VhostUserRequest;
 
diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virtio/vhost-backend.h
index daf9180c33..730e24c33b 100644
--- a/include/hw/virtio/vhost-backend.h
+++ b/include/hw/virtio/vhost-backend.h
@@ -164,5 +164,6 @@ int vhost_backend_handle_iotlb_msg(struct vhost_dev *dev,
 int vhost_user_input_get_config(struct vhost_dev *dev,
                                 struct virtio_input_config **config);
 int vhost_user_gpu_set_socket(struct vhost_dev *dev, int fd);
+int vhost_user_gpu_get_num_capsets(struct vhost_dev *dev, uint32_t *num);
 
 #endif /* VHOST_BACKEND_H */
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 8c1a1742b0..bfec6528f2 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -91,6 +91,7 @@ typedef enum VhostUserRequest {
     VHOST_USER_POSTCOPY_END     = 30,
     VHOST_USER_INPUT_GET_CONFIG = 31,
     VHOST_USER_GPU_SET_SOCKET   = 32,
+    VHOST_USER_GPU_GET_NUM_CAPSETS = 33,
     VHOST_USER_MAX
 } VhostUserRequest;
 
@@ -922,6 +923,20 @@ static int vhost_user_get_u64(struct vhost_dev *dev, int request, uint64_t *u64)
     return 0;
 }
 
+int vhost_user_gpu_get_num_capsets(struct vhost_dev *dev, uint32_t *num)
+{
+    uint64_t u64;
+
+    if (vhost_user_get_u64(dev, VHOST_USER_GPU_GET_NUM_CAPSETS, &u64) < 0) {
+        return -1;
+    }
+    if (u64 > INT32_MAX) {
+        return -1;
+    }
+    *num = u64;
+    return 0;
+}
+
 static int vhost_user_get_features(struct vhost_dev *dev, uint64_t *features)
 {
     return vhost_user_get_u64(dev, VHOST_USER_GET_FEATURES, features);
diff --git a/docs/interop/vhost-user.txt b/docs/interop/vhost-user.txt
index c4c063a8c0..ba5e37d714 100644
--- a/docs/interop/vhost-user.txt
+++ b/docs/interop/vhost-user.txt
@@ -777,6 +777,14 @@ Master message types
       ancillary data. The GPU protocol is used to inform the master of
       rendering state and updates. See vhost-user-gpu.rst for details.
 
+ * VHOST_USER_GPU_GET_NUM_CAPSETS
+      Id: 33
+      Master payload: N/A
+      Slave payload: u64
+
+      Get the virtio-gpu 'num_capsets' config value. For non-virgl
+      rendering, the value can be 0.
+
 Slave message types
 -------------------
 
-- 
2.18.0.129.ge3331758f1