1 files changed, 150 insertions, 0 deletions
diff --git a/app/utils.cpp b/app/utils.cpp
new file mode 100644
index 0000000..f1c3eae
--- /dev/null
+++ b/app/utils.cpp
@@ -0,0 +1,150 @@
+#include <sys/mman.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <assert.h>
+#include <cstdlib>
+#include <cstring>
+#include <cerrno>
+
+#include "utils.h"
+
+static int
+os_fd_set_cloexec(int fd)
+{
+	long flags;
+
+	if (fd == -1)
+		return -1;
+
+	flags = fcntl(fd, F_GETFD);
+	if (flags == -1)
+		return -1;
+
+	if (fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == -1)
+		return -1;
+
+	return 0;
+}
+
+static int
+set_cloexec_or_close(int fd)
+{
+	if (os_fd_set_cloexec(fd) != 0) {
+		close(fd);
+		return -1;
+	}
+	return fd;
+}
+
+static int
+create_tmpfile_cloexec(char *tmpname)
+{
+	int fd;
+
+#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
+
+	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.
+ *
+ * If the C library implements memfd_create(), it is used to create the
+ * file purely in memory, without any backing file name on the file
+ * system, and then sealing off the possibility of shrinking it.  This
+ * can then be checked before accessing mmap()'ed file contents, to
+ * make sure SIGBUS can't happen.  It also avoids requiring
+ * XDG_RUNTIME_DIR.
+ */
+int
+os_create_anonymous_file(off_t size)
+{
+	static const char weston_template[] = "/weston-shared-XXXXXX";
+	const char *path;
+	char *name;
+	int fd;
+	int ret;
+
+#ifdef HAVE_MEMFD_CREATE
+	fd = memfd_create("weston-shared", MFD_CLOEXEC | MFD_ALLOW_SEALING);
+	if (fd >= 0) {
+		/* We can add this seal before calling posix_fallocate(), as
+		 * the file is currently zero-sized anyway.
+		 *
+		 * There is also no need to check for the return value, we
+		 * couldn't do anything with it anyway.
+		 */
+		fcntl(fd, F_ADD_SEALS, F_SEAL_SHRINK);
+	} else
+#endif
+	{
+		path = getenv("XDG_RUNTIME_DIR");
+		if (!path) {
+			errno = ENOENT;
+			return -1;
+		}
+
+		name = static_cast<char *>(malloc(strlen(path) + sizeof(weston_template)));
+		if (!name)
+			return -1;
+
+		strcpy(name, path);
+		strcat(name, weston_template);
+
+		fd = create_tmpfile_cloexec(name);
+
+		free(name);
+
+		if (fd < 0)
+			return -1;
+	}
+
+#ifdef HAVE_POSIX_FALLOCATE
+	do {
+		ret = posix_fallocate(fd, 0, size);
+	} while (ret == EINTR);
+	if (ret != 0) {
+		close(fd);
+		errno = ret;
+		return -1;
+	}
+#else
+	do {
+		ret = ftruncate(fd, size);
+	} while (ret < 0 && errno == EINTR);
+	if (ret < 0) {
+		close(fd);
+		return -1;
+	}
+#endif
+
+	return fd;
+}