vtest: --multi-clients requires version 3

Protocol version 3 uses server-generated, rather than client-generated,
resource ids.  Without that, clients could pick conflicting resource
ids.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Ryan Neph <ryanneph@google.com>
Reviewed-by: Gert Wollny <gert.wollny@collabora.com>

vtest/vtest_renderer.c

@@ -444,6 +444,9 @@ int vtest_lazy_init_context(struct vtest_context *ctx)
    if (ctx->context_initialized)
       return 0;
 
+   if (renderer.multi_clients && ctx->protocol_version < 3)
+      return report_failed_call("protocol version too low", -EINVAL);
+
    if (ctx->capset_id) {
       ret = virgl_renderer_context_create_with_flags(ctx->ctx_id,
                                                      ctx->capset_id,
@@ -530,6 +533,9 @@ int vtest_protocol_version(UNUSED uint32_t length_dw)
       version = 0;
    }
 
+   if (renderer.multi_clients && version < 3)
+      return report_failed_call("protocol version too low", -EINVAL);
+
    ctx->protocol_version = version;
 
    hdr_buf[VTEST_CMD_LEN] = VCMD_PROTOCOL_VERSION_SIZE;

vtest/vtest_server.c

@@ -186,7 +186,7 @@ static void vtest_server_parse_args(int argc, char **argv)
          server.loop = false;
          break;
       case OPT_MULTI_CLIENTS:
-         printf("EXPERIMENTAL: clients must know and trust each other\n");
+         printf("multi-clients enabled: clients must trust each other\n");
          server.multi_clients = true;
          break;
       case OPT_USE_GLX: