2 files changed, 35 insertions, 0 deletions
diff --git a/src/shared/path-util.c b/src/shared/path-util.c
index 665b171263..0744563976 100644
--- a/src/shared/path-util.c
+++ b/src/shared/path-util.c
@@ -539,3 +539,37 @@ bool paths_check_timestamp(const char* const* paths, usec_t *timestamp, bool upd
 
         return changed;
 }
+
+char *prefix_root(const char *root, const char *path) {
+        char *n, *p;
+        size_t l;
+
+        /* If root is passed, prefixes path with it. Otherwise returns
+         * it as is. */
+
+        assert(path);
+
+        /* First, drop duplicate prefixing slashes from the path */
+        while (path[0] == '/' && path[1] == '/')
+                path++;
+
+        if (isempty(root) || path_equal(root, "/"))
+                return strdup(path);
+
+        l = strlen(root) + 1 + strlen(path) + 1;
+
+        n = new(char, l);
+        if (!n)
+                return NULL;
+
+        p = stpcpy(n, root);
+
+        while (p > n && p[-1] == '/')
+                p--;
+
+        if (path[0] != '/')
+                *(p++) = '/';
+
+        strcpy(p, path);
+        return n;
+}
diff --git a/src/shared/path-util.h b/src/shared/path-util.h
index 56d1c52ae2..0123c2609c 100644
--- a/src/shared/path-util.h
+++ b/src/shared/path-util.h
@@ -38,3 +38,4 @@ int fd_is_mount_point(int fd);
 int path_is_mount_point(const char *path, bool allow_symlink);
 bool paths_check_timestamp(const char* const* paths, usec_t *paths_ts_usec, bool update);
 
+char *prefix_root(const char *root, const char *path);