util: add generic calls for prefixing a root directory to a path

[elogind.git] / src / shared / path-util.h

diff --git a/src/shared/path-util.h b/src/shared/path-util.h
index 5548ce4a9410b33be21316e8c74071cd05141ec2..4f45cfd2b7ddf34778e4b8772c63cb517d205b02 100644 (file)
--- a/src/shared/path-util.h
+++ b/src/shared/path-util.h
@@ -73,3 +73,30 @@ int fsck_exists(const char *fstype);
 /* Same as PATH_FOREACH_PREFIX but also includes the specified path itself */
 #define PATH_FOREACH_PREFIX_MORE(prefix, path) \
         for (char *_slash = ({ path_kill_slashes(strcpy(prefix, path)); if (streq(prefix, "/")) prefix[0] = 0; strrchr(prefix, 0); }); _slash && ((*_slash = 0), true); _slash = strrchr((prefix), '/'))
+
+char *prefix_root(const char *root, const char *path);
+
+/* Similar to prefix_root(), but returns an alloca() buffer, or
+ * possibly a const pointer into the path parameter */
+#define prefix_roota(root, path)                                        \
+        ({                                                              \
+                const char* _path = (path), *_root = (root), *_ret;     \
+                char *_p, *_n;                                          \
+                size_t _l;                                              \
+                while (_path[0] == '/' && _path[1] == '/')              \
+                        _path ++;                                       \
+                if (isempty(_root) || path_equal(_root, "/"))           \
+                        _ret = _path;                                   \
+                else {                                                  \
+                        _l = strlen(_root) + 1 + strlen(_path) + 1;     \
+                        _n = alloca(_l);                                \
+                        _p = stpcpy(_n, _root);                         \
+                        while (_p > _n && _p[-1] == '/')                \
+                                _p--;                                   \
+                        if (_path[0] != '/')                            \
+                                *(_p++) = '/';                          \
+                        strcpy(_p, _path);                              \
+                        _ret = _n;                                      \
+                }                                                       \
+                _ret;                                                   \
+        })