frontend: Use enums for backend type, not strings

Convert our backend type to an enum early, and use it in place of a
string.

Signed-off-by: Daniel Stone <daniels@collabora.com>

compositor/config-helpers.c

@@ -0,0 +1,64 @@
+/*
+ * Copyright 2022 Collabora, Ltd.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "config.h"
+
+#include <string.h>
+
+#include <libweston/libweston.h>
+#include <libweston/config-parser.h>
+
+#include "shared/helpers.h"
+#include "weston-private.h"
+
+struct {
+	char *short_name;
+	char *long_name;
+	enum weston_compositor_backend backend;
+} backend_name_map[] = {
+	{ "drm", "drm-backend.so", WESTON_BACKEND_DRM },
+	{ "headless", "headless-backend.so", WESTON_BACKEND_HEADLESS },
+	{ "rdp", "rdp-backend.so", WESTON_BACKEND_RDP },
+	{ "vnc", "vnc-backend.so", WESTON_BACKEND_VNC },
+	{ "wayland", "wayland-backend.so", WESTON_BACKEND_WAYLAND },
+	{ "x11", "x11-backend.so", WESTON_BACKEND_X11 },
+};
+
+bool
+get_backend_from_string(const char *name,
+			enum weston_compositor_backend *backend)
+{
+	size_t i;
+
+	for (i = 0; i < ARRAY_LENGTH(backend_name_map); i++) {
+		if (strcmp(name, backend_name_map[i].short_name) == 0 ||
+		    strcmp(name, backend_name_map[i].long_name) == 0) {
+			*backend = backend_name_map[i].backend;
+			return true;
+		}
+	}
+
+	return false;
+}

compositor/main.c

@@ -3481,30 +3481,32 @@ load_wayland_backend(struct weston_compositor *c,
 
 
 static int
-load_backend(struct weston_compositor *compositor, const char *backend,
+load_backend(struct weston_compositor *compositor, const char *name,
 	     int *argc, char **argv, struct weston_config *config)
 {
-	if (strcmp(backend, "headless") == 0 ||
-	    strstr(backend, "headless-backend.so"))
-		return load_headless_backend(compositor, argc, argv, config);
-	else if (strcmp(backend, "rdp") == 0 ||
-		 strstr(backend, "rdp-backend.so"))
-		return load_rdp_backend(compositor, argc, argv, config);
-	else if (strcmp(backend, "vnc") == 0 ||
-		 strstr(backend, "vnc-backend.so"))
-		return load_vnc_backend(compositor, argc, argv, config);
-	else if (strcmp(backend, "drm") == 0 ||
-		 strstr(backend, "drm-backend.so"))
-		return load_drm_backend(compositor, argc, argv, config);
-	else if (strcmp(backend, "x11") == 0 ||
-		 strstr(backend, "x11-backend.so"))
-		return load_x11_backend(compositor, argc, argv, config);
-	else if (strcmp(backend, "wayland") == 0 ||
-		 strstr(backend, "wayland-backend.so"))
-		return load_wayland_backend(compositor, argc, argv, config);
+	enum weston_compositor_backend backend;
 
-	weston_log("Error: unknown backend \"%s\"\n", backend);
-	return -1;
+	if (!get_backend_from_string(name, &backend)) {
+		weston_log("Error: unknown backend \"%s\"\n", name);
+		return -1;
+	}
+
+	switch (backend) {
+	case WESTON_BACKEND_DRM:
+		return load_drm_backend(compositor, argc, argv, config);
+	case WESTON_BACKEND_HEADLESS:
+		return load_headless_backend(compositor, argc, argv, config);
+	case WESTON_BACKEND_RDP:
+		return load_rdp_backend(compositor, argc, argv, config);
+	case WESTON_BACKEND_VNC:
+		return load_vnc_backend(compositor, argc, argv, config);
+	case WESTON_BACKEND_WAYLAND:
+		return load_wayland_backend(compositor, argc, argv, config);
+	case WESTON_BACKEND_X11:
+		return load_x11_backend(compositor, argc, argv, config);
+	default:
+		unreachable("unknown backend type in load_backend()");
+	}
 }
 
 static char *

compositor/meson.build

@@ -2,6 +2,7 @@ srcs_weston = [
 	git_version_h,
 	'main.c',
 	'text-backend.c',
+	'config-helpers.c',
 	'weston-screenshooter.c',
 	text_input_unstable_v1_server_protocol_h,
 	text_input_unstable_v1_protocol_c,

compositor/weston-private.h

@@ -28,6 +28,10 @@
 #include <libweston/libweston.h>
 #include <libweston/config-parser.h>
 
+bool
+get_backend_from_string(const char *name,
+			enum weston_compositor_backend *backend);
+
 int
 wet_output_set_color_characteristics(struct weston_output *output,
 				     struct weston_config *wc,