output: introduce wlr_output_set_name

wlroots picks names for all outputs, but it might be desirable for
compositor to override it.

For instance, Sway will use a headless output as a fallback in
case no outputs are connected. Sway wants to clearly label the
fallback output as such and label "real" headless outputs starting
from HEADLESS-1.

backend/drm/drm.c

@@ -1299,8 +1299,7 @@ void scan_drm_connectors(struct wlr_drm_backend *drm,
 			wlr_output_init(&wlr_conn->output, &drm->backend, &output_impl,
 				drm->display);
 
-			memcpy(wlr_conn->output.name, wlr_conn->name,
-				sizeof(wlr_conn->output.name));
+			wlr_output_set_name(&wlr_conn->output, wlr_conn->name);
 
 			wlr_conn->output.phys_width = drm_conn->mmWidth;
 			wlr_conn->output.phys_height = drm_conn->mmHeight;

backend/headless/output.c

@@ -116,8 +116,10 @@ struct wlr_output *wlr_headless_add_output(struct wlr_backend *wlr_backend,
 	output_set_custom_mode(output, width, height, 0);
 	strncpy(wlr_output->make, "headless", sizeof(wlr_output->make));
 	strncpy(wlr_output->model, "headless", sizeof(wlr_output->model));
-	snprintf(wlr_output->name, sizeof(wlr_output->name), "HEADLESS-%zd",
-		++backend->last_output_num);
+
+	char name[64];
+	snprintf(name, sizeof(name), "HEADLESS-%zd", ++backend->last_output_num);
+	wlr_output_set_name(wlr_output, name);
 
 	char description[128];
 	snprintf(description, sizeof(description),

backend/wayland/output.c

@@ -520,8 +520,10 @@ struct wlr_output *wlr_wl_output_create(struct wlr_backend *wlr_backend) {
 	wlr_output_update_custom_mode(wlr_output, 1280, 720, 0);
 	strncpy(wlr_output->make, "wayland", sizeof(wlr_output->make));
 	strncpy(wlr_output->model, "wayland", sizeof(wlr_output->model));
-	snprintf(wlr_output->name, sizeof(wlr_output->name), "WL-%zd",
-		++backend->last_output_num);
+
+	char name[64];
+	snprintf(name, sizeof(name), "WL-%zd", ++backend->last_output_num);
+	wlr_output_set_name(wlr_output, name);
 
 	char description[128];
 	snprintf(description, sizeof(description),

backend/x11/output.c

@@ -512,8 +512,10 @@ struct wlr_output *wlr_x11_output_create(struct wlr_backend *backend) {
 
 	wlr_output_update_custom_mode(wlr_output, 1024, 768, 0);
 
-	snprintf(wlr_output->name, sizeof(wlr_output->name), "X11-%zd",
-		++x11->last_output_num);
+	char name[64];
+	snprintf(name, sizeof(name), "X11-%zd", ++x11->last_output_num);
+	wlr_output_set_name(wlr_output, name);
+
 	parse_xcb_setup(wlr_output, x11->xcb);
 
 	char description[128];

include/wlr/types/wlr_output.h

@@ -118,7 +118,7 @@ struct wlr_output {
 	struct wl_global *global;
 	struct wl_list resources;
 
-	char name[24];
+	char *name;
 	char *description; // may be NULL
 	char make[56];
 	char model[16];
@@ -336,6 +336,17 @@ void wlr_output_set_render_format(struct wlr_output *output, uint32_t format);
 void wlr_output_set_scale(struct wlr_output *output, float scale);
 void wlr_output_set_subpixel(struct wlr_output *output,
 	enum wl_output_subpixel subpixel);
+/**
+ * Set the output name.
+ *
+ * Output names are subject to the following rules:
+ *
+ * - Each output name must be unique.
+ * - The name cannot change after the output has been advertised to clients.
+ *
+ * For more details, see the protocol documentation for wl_output.name.
+ */
+void wlr_output_set_name(struct wlr_output *output, const char *name);
 void wlr_output_set_description(struct wlr_output *output, const char *desc);
 /**
  * Schedule a done event.

types/output/output.c

@@ -324,6 +324,13 @@ void wlr_output_set_subpixel(struct wlr_output *output,
 	wlr_output_schedule_done(output);
 }
 
+void wlr_output_set_name(struct wlr_output *output, const char *name) {
+	assert(output->global == NULL);
+
+	free(output->name);
+	output->name = strdup(name);
+}
+
 void wlr_output_set_description(struct wlr_output *output, const char *desc) {
 	if (output->description != NULL && desc != NULL &&
 			strcmp(output->description, desc) == 0) {
@@ -420,6 +427,7 @@ void wlr_output_destroy(struct wlr_output *output) {
 		wl_event_source_remove(output->idle_done);
 	}
 
+	free(output->name);
 	free(output->description);
 
 	pixman_region32_fini(&output->pending.damage);