Use shm_open instead of XDG_RUNTIME_DIR

buffer.c

@@ -1,30 +1,48 @@
-#define _XOPEN_SOURCE 500
+#define _POSIX_C_SOURCE 200112L
+#include <errno.h>
+#include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mman.h>
+#include <time.h>
 #include <unistd.h>
 
 #include "buffer.h"
 
-static int create_pool_file(size_t size, char **name) {
-	static const char template[] = "grim-XXXXXX";
-	const char *path = getenv("XDG_RUNTIME_DIR");
-	if (path == NULL) {
-		return -1;
+static void randname(char *buf) {
+	struct timespec ts;
+	clock_gettime(CLOCK_REALTIME, &ts);
+	long r = ts.tv_nsec;
+	for (int i = 0; i < 6; ++i) {
+		buf[i] = 'A'+(r&15)+(r&16)*2;
+		r >>= 5;
 	}
+}
 
-	int ts = (path[strlen(path) - 1] == '/');
+static int anonymous_shm_open(void) {
+	char name[] = "/grim-XXXXXX";
+	int retries = 100;
 
-	*name = malloc(
-		strlen(template) +
-		strlen(path) +
-		(ts ? 0 : 1) + 1);
-	sprintf(*name, "%s%s%s", path, ts ? "" : "/", template);
+	do {
+		randname(name + strlen(name) - 6);
 
-	int fd = mkstemp(*name);
+		--retries;
+		// shm_open guarantees that O_CLOEXEC is set
+		int fd = shm_open(name, O_RDWR | O_CREAT | O_EXCL, 0600);
+		if (fd >= 0) {
+			shm_unlink(name);
+			return fd;
+		}
+	} while (retries > 0 && errno == EEXIST);
+
+	return -1;
+}
+
+static int create_shm_file(off_t size) {
+	int fd = anonymous_shm_open();
 	if (fd < 0) {
-		return -1;
+		return fd;
 	}
 
 	if (ftruncate(fd, size) < 0) {
@@ -39,16 +57,14 @@ struct grim_buffer *create_buffer(struct wl_shm *shm, enum wl_shm_format format,
 		int32_t width, int32_t height, int32_t stride) {
 	size_t size = stride * height;
 
-	char *name;
-	int fd = create_pool_file(size, &name);
+	int fd = create_shm_file(size);
 	if (fd == -1) {
 		return NULL;
 	}
 
 	void *data = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
 	if (data == MAP_FAILED) {
-		unlink(name);
-		free(name);
+		close(fd);
 		return NULL;
 	}
 
@@ -58,9 +74,6 @@ struct grim_buffer *create_buffer(struct wl_shm *shm, enum wl_shm_format format,
 	wl_shm_pool_destroy(pool);
 
 	close(fd);
-	fd = -1;
-	unlink(name);
-	free(name);
 
 	struct grim_buffer *buffer = calloc(1, sizeof(struct grim_buffer));
 	buffer->wl_buffer = wl_buffer;

meson.build

@@ -16,11 +16,13 @@ add_project_arguments('-Wno-unused-parameter', language: 'c')
 grim_inc = include_directories('include')
 
 cc = meson.get_compiler('c')
+
 cairo = dependency('cairo')
-wayland_client = dependency('wayland-client')
-wayland_protos = dependency('wayland-protocols', version: '>=1.14')
 jpeg = dependency('libjpeg')
 math = cc.find_library('m')
+realtime = cc.find_library('rt')
+wayland_client = dependency('wayland-client')
+wayland_protos = dependency('wayland-protocols', version: '>=1.14')
 
 subdir('protocol')
 
@@ -39,6 +41,7 @@ executable(
 		client_protos,
 		jpeg,
 		math,
+		realtime,
 		wayland_client,
 	],
 	include_directories: [grim_inc],