fs-util: introduce mkfifoat_atomic() helper

src/basic/fs-util.c

@@ -435,6 +435,31 @@ int mkfifo_atomic(const char *path, mode_t mode) {
         return 0;
 }
 
+int mkfifoat_atomic(int dirfd, const char *path, mode_t mode) {
+        _cleanup_free_ char *t = NULL;
+        int r;
+
+        assert(path);
+
+        if (path_is_absolute(path))
+                return mkfifo_atomic(path, mode);
+
+        /* We're only interested in the (random) filename.  */
+        r = tempfn_random_child("", NULL, &t);
+        if (r < 0)
+                return r;
+
+        if (mkfifoat(dirfd, t, mode) < 0)
+                return -errno;
+
+        if (renameat(dirfd, t, dirfd, path) < 0) {
+                unlink_noerrno(t);
+                return -errno;
+        }
+
+        return 0;
+}
+
 int get_files_in_directory(const char *path, char ***list) {
         _cleanup_closedir_ DIR *d = NULL;
         struct dirent *de;

src/basic/fs-util.h

@@ -42,6 +42,7 @@ int symlink_idempotent(const char *from, const char *to);
 int symlink_atomic(const char *from, const char *to);
 int mknod_atomic(const char *path, mode_t mode, dev_t dev);
 int mkfifo_atomic(const char *path, mode_t mode);
+int mkfifoat_atomic(int dir_fd, const char *path, mode_t mode);
 
 int get_files_in_directory(const char *path, char ***list);