util: use shm_open for in-memory files

shm_open is a POSIX function creating an in-memory file. Using it simplifies
the code and removes the dependency on XDG_RUNTIME_DIR. The only downside is
that we need to generate a random name for the shm file.

3 files changed, 69 insertions, 151 deletions

diff --git a/util/meson.build b/util/meson.build
index f9d1997d..dca3e9a4 100644
--- a/util/meson.build
+++ b/util/meson.build
@@ -3,10 +3,10 @@ lib_wlr_util = static_library(
 	files(
 		'array.c',
 		'log.c',
-		'os-compatibility.c',
 		'region.c',
+		'shm.c',
 		'signal.c',
 	),
 	include_directories: wlr_inc,
-	dependencies: [wayland_server, pixman],
+	dependencies: [wayland_server, pixman, rt],
 )
diff --git a/util/os-compatibility.c b/util/os-compatibility.c
deleted file mode 100644
index bd39705d..00000000
--- a/util/os-compatibility.c
+++ /dev/null
@@ -1,149 +0,0 @@
-/*
- * Copyright © 2012 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.
- */
-
-#define _POSIX_C_SOURCE 200809L
-#include <errno.h>
-#include <fcntl.h>
-#include <stdlib.h>
-#include <string.h>
-#include <sys/socket.h>
-#include <sys/stat.h>
-#include <sys/types.h>
-#include <unistd.h>
-#include <wlr/config.h>
-#include "util/os-compatibility.h"
-
-int os_fd_set_cloexec(int fd) {
-	if (fd == -1) {
-		return -1;
-	}
-
-	long flags = fcntl(fd, F_GETFD);
-	if (flags == -1) {
-		return -1;
-	}
-
-	if (fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == -1) {
-		return -1;
-	}
-
-	return 0;
-}
-
-int set_cloexec_or_close(int fd) {
-	if (os_fd_set_cloexec(fd) != 0) {
-		close(fd);
-		return -1;
-	}
-	return fd;
-}
-
-int create_tmpfile_cloexec(char *tmpname) {
-	int fd;
-	mode_t prev_umask = umask(0066);
-#ifdef HAVE_MKOSTEMP
-	fd = mkostemp(tmpname, O_CLOEXEC);
-	if (fd >= 0) {
-		unlink(tmpname);
-	}
-#else
-	fd = mkstemp(tmpname);
-	if (fd >= 0) {
-		fd = set_cloexec_or_close(fd);
-		unlink(tmpname);
-	}
-#endif
-	umask(prev_umask);
-
-	return fd;
-}
-
-/*
- * Create a new, unique, anonymous file of the given size, and
- * return the file descriptor for it. The file descriptor is set
- * CLOEXEC. The file is immediately suitable for mmap()'ing
- * the given size at offset zero.
- *
- * The file should not have a permanent backing store like a disk,
- * but may have if XDG_RUNTIME_DIR is not properly implemented in OS.
- *
- * The file name is deleted from the file system.
- *
- * The file is suitable for buffer sharing between processes by
- * transmitting the file descriptor over Unix sockets using the
- * SCM_RIGHTS methods.
- *
- * If the C library implements posix_fallocate(), it is used to
- * guarantee that disk space is available for the file at the
- * given size. If disk space is insufficient, errno is set to ENOSPC.
- * If posix_fallocate() is not supported, program may receive
- * SIGBUS on accessing mmap()'ed file contents instead.
- */
-int os_create_anonymous_file(off_t size) {
-	static const char template[] = "/wlroots-shared-XXXXXX";
-
-	const char *path = getenv("XDG_RUNTIME_DIR");
-	if (!path) {
-		errno = ENOENT;
-		return -1;
-	}
-
-	char *name = malloc(strlen(path) + sizeof(template));
-	if (!name) {
-		return -1;
-	}
-
-	strcpy(name, path);
-	strcat(name, template);
-
-	int fd = create_tmpfile_cloexec(name);
-	free(name);
-	if (fd < 0) {
-		return -1;
-	}
-
-#ifdef WLR_HAS_POSIX_FALLOCATE
-	int ret;
-	do {
-		ret = posix_fallocate(fd, 0, size);
-	} while (ret == EINTR);
-	if (ret != 0) {
-		close(fd);
-		errno = ret;
-		return -1;
-	}
-#else
-	int ret;
-	do {
-		ret = ftruncate(fd, size);
-	} while (ret < 0 && errno == EINTR);
-	if (ret < 0) {
-		close(fd);
-		return -1;
-	}
-#endif
-
-	return fd;
-}
diff --git a/util/shm.c b/util/shm.c
new file mode 100644
index 00000000..3783e473
--- /dev/null
+++ b/util/shm.c
@@ -0,0 +1,67 @@
+#define _POSIX_C_SOURCE 200112L
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <time.h>
+#include <unistd.h>
+#include <wlr/config.h>
+#include "util/shm.h"
+
+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 create_shm_file(void) {
+	int retries = 100;
+	do {
+		char name[] = "/wlroots-XXXXXX";
+		randname(name + strlen(name) - 6);
+
+		--retries;
+		// CLOEXEC is guaranteed to be set by shm_open
+		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;
+}
+
+int allocate_shm_file(size_t size) {
+	int fd = create_shm_file();
+	if (fd < 0) {
+		return -1;
+	}
+
+#ifdef WLR_HAS_POSIX_FALLOCATE
+	int ret;
+	do {
+		ret = posix_fallocate(fd, 0, size);
+	} while (ret == EINTR);
+	if (ret != 0) {
+		close(fd);
+		errno = ret;
+		return -1;
+	}
+#else
+	int ret;
+	do {
+		ret = ftruncate(fd, size);
+	} while (ret < 0 && errno == EINTR);
+	if (ret < 0) {
+		close(fd);
+		return -1;
+	}
+#endif
+
+	return fd;
+}