+
+int open_tmpfile_unlinkable(const char *directory, int flags) {
+ char *p;
+ int fd;
+
+ assert(directory);
+
+ /* Returns an unlinked temporary file that cannot be linked into the file system anymore */
+
+#ifdef O_TMPFILE
+ /* Try O_TMPFILE first, if it is supported */
+ fd = open(directory, flags|O_TMPFILE|O_EXCL, S_IRUSR|S_IWUSR);
+ if (fd >= 0)
+ return fd;
+#endif
+
+ /* Fall back to unguessable name + unlinking */
+ p = strjoina(directory, "/systemd-tmp-XXXXXX");
+
+ fd = mkostemp_safe(p, flags);
+ if (fd < 0)
+ return fd;
+
+ (void) unlink(p);
+
+ return fd;
+}
+
+int open_tmpfile_linkable(const char *target, int flags, char **ret_path) {
+ _cleanup_free_ char *tmp = NULL;
+ int r, fd;
+
+ assert(target);
+ assert(ret_path);
+
+ /* Don't allow O_EXCL, as that has a special meaning for O_TMPFILE */
+ assert((flags & O_EXCL) == 0);
+
+ /* Creates a temporary file, that shall be renamed to "target" later. If possible, this uses O_TMPFILE – in
+ * which case "ret_path" will be returned as NULL. If not possible a the tempoary path name used is returned in
+ * "ret_path". Use link_tmpfile() below to rename the result after writing the file in full. */
+
+#ifdef O_TMPFILE
+ {
+ _cleanup_free_ char *dn = NULL;
+
+ dn = dirname_malloc(target);
+ if (!dn)
+ return -ENOMEM;
+
+ fd = open(dn, O_TMPFILE|flags, 0640);
+ if (fd >= 0) {
+ *ret_path = NULL;
+ return fd;
+ }
+
+ log_debug_errno(errno, "Failed to use O_TMPFILE on %s: %m", dn);
+ }
+#endif
+
+ r = tempfn_random(target, NULL, &tmp);
+ if (r < 0)
+ return r;
+
+ fd = open(tmp, O_CREAT|O_EXCL|O_NOFOLLOW|O_NOCTTY|flags, 0640);
+ if (fd < 0)
+ return -errno;
+
+ *ret_path = tmp;
+ tmp = NULL;
+
+ return fd;
+}
+
+int link_tmpfile(int fd, const char *path, const char *target) {
+
+ assert(fd >= 0);
+ assert(target);
+
+ /* Moves a temporary file created with open_tmpfile() above into its final place. if "path" is NULL an fd
+ * created with O_TMPFILE is assumed, and linkat() is used. Otherwise it is assumed O_TMPFILE is not supported
+ * on the directory, and renameat2() is used instead.
+ *
+ * Note that in both cases we will not replace existing files. This is because linkat() does not support this
+ * operation currently (renameat2() does), and there is no nice way to emulate this. */
+
+ if (path) {
+ if (rename_noreplace(AT_FDCWD, path, AT_FDCWD, target) < 0)
+ return -errno;
+ } else {
+ char proc_fd_path[strlen("/proc/self/fd/") + DECIMAL_STR_MAX(fd) + 1];
+
+ xsprintf(proc_fd_path, "/proc/self/fd/%i", fd);
+
+ if (linkat(AT_FDCWD, proc_fd_path, AT_FDCWD, target, AT_SYMLINK_FOLLOW) < 0)
+ return -errno;
+ }
+
+ return 0;
+}