render/egl: don't rely on being able to open primary node

On some setups (e.g. remote access via SSH) the current user won't have
the permission to open the primary node at all. It's still possible to
use drmGetDevices to match the primary node name returned by EGL.

Closes: https://github.com/swaywm/wlroots/issues/2488

render/egl.c

@@ -854,6 +854,62 @@ bool wlr_egl_destroy_surface(struct wlr_egl *egl, EGLSurface surface) {
 	return eglDestroySurface(egl->display, surface);
 }
 
+static bool device_has_name(const drmDevice *device, const char *name) {
+	for (size_t i = 0; i < DRM_NODE_MAX; i++) {
+		if (!(device->available_nodes & (1 << i))) {
+			continue;
+		}
+		if (strcmp(device->nodes[i], name) == 0) {
+			return true;
+		}
+	}
+	return false;
+}
+
+static char *get_render_name(const char *name) {
+	uint32_t flags = 0;
+	int devices_len = drmGetDevices2(flags, NULL, 0);
+	if (devices_len < 0) {
+		wlr_log(WLR_ERROR, "drmGetDevices2 failed");
+		return NULL;
+	}
+	drmDevice **devices = calloc(devices_len, sizeof(drmDevice *));
+	if (devices == NULL) {
+		wlr_log_errno(WLR_ERROR, "Allocation failed");
+		return NULL;
+	}
+	devices_len = drmGetDevices2(flags, devices, devices_len);
+	if (devices_len < 0) {
+		free(devices);
+		wlr_log(WLR_ERROR, "drmGetDevices2 failed");
+		return NULL;
+	}
+
+	const drmDevice *match = NULL;
+	for (int i = 0; i < devices_len; i++) {
+		if (device_has_name(devices[i], name)) {
+			match = devices[i];
+			break;
+		}
+	}
+
+	char *render_name = NULL;
+	if (match == NULL) {
+		wlr_log(WLR_ERROR, "Cannot find DRM device %s", name);
+	} else if (!(match->available_nodes & (1 << DRM_NODE_RENDER))) {
+		wlr_log(WLR_ERROR, "DRM device %s has no render node", name);
+	} else {
+		render_name = strdup(match->nodes[DRM_NODE_RENDER]);
+	}
+
+	for (int i = 0; i < devices_len; i++) {
+		drmFreeDevice(&devices[i]);
+	}
+	free(devices);
+
+	return render_name;
+}
+
 int wlr_egl_dup_drm_fd(struct wlr_egl *egl) {
 	if (egl->device == EGL_NO_DEVICE_EXT || !egl->exts.device_drm_ext) {
 		return -1;
@@ -867,25 +923,21 @@ int wlr_egl_dup_drm_fd(struct wlr_egl *egl) {
 		return -1;
 	}
 
-	int primary_fd = open(primary_name, O_RDWR | O_NONBLOCK | O_CLOEXEC);
-	if (primary_fd < 0) {
-		wlr_log_errno(WLR_ERROR, "Failed to open primary DRM device");
-		return -1;
-	}
-
-	char *render_name = drmGetRenderDeviceNameFromFd(primary_fd);
+	char *render_name = get_render_name(primary_name);
 	if (render_name == NULL) {
-		wlr_log_errno(WLR_ERROR, "drmGetRenderDeviceNameFromFd failed");
-		close(primary_fd);
+		wlr_log(WLR_ERROR, "Can't find render node name for device %s",
+			primary_name);
 		return -1;
 	}
-	close(primary_fd);
 
 	int render_fd = open(render_name, O_RDWR | O_NONBLOCK | O_CLOEXEC);
 	if (render_fd < 0) {
-		wlr_log_errno(WLR_ERROR, "Failed to open render DRM device");
+		wlr_log_errno(WLR_ERROR, "Failed to open DRM render node %s",
+			render_name);
+		free(render_name);
 		return -1;
 	}
+	free(render_name);
 
 	return render_fd;
 }