+/* Like readlink(), but returns the link name as a null-terminated string in
+ * allocated memory that the caller must eventually free (with free()).
+ * Returns NULL on error, in which case errno is set appropriately. */
+char *
+xreadlink(const char *filename)
+{
+ size_t size;
+
+ for (size = 64; ; size *= 2) {
+ char *buf = xmalloc(size);
+ ssize_t retval = readlink(filename, buf, size);
+ int error = errno;
+
+ if (retval >= 0 && retval < size) {
+ buf[retval] = '\0';
+ return buf;
+ }
+
+ free(buf);
+ if (retval < 0) {
+ errno = error;
+ return NULL;
+ }
+ }
+}
+
+/* Returns a version of 'filename' with symlinks in the final component
+ * dereferenced. This differs from realpath() in that:
+ *
+ * - 'filename' need not exist.
+ *
+ * - If 'filename' does exist as a symlink, its referent need not exist.
+ *
+ * - Only symlinks in the final component of 'filename' are dereferenced.
+ *
+ * The caller must eventually free the returned string (with free()). */
+char *
+follow_symlinks(const char *filename)
+{
+ struct stat s;
+ char *fn;
+ int i;
+
+ fn = xstrdup(filename);
+ for (i = 0; i < 10; i++) {
+ char *linkname;
+ char *next_fn;
+
+ if (lstat(fn, &s) != 0 || !S_ISLNK(s.st_mode)) {
+ return fn;
+ }
+
+ linkname = xreadlink(fn);
+ if (!linkname) {
+ VLOG_WARN("%s: readlink failed (%s)",
+ filename, ovs_strerror(errno));
+ return fn;
+ }
+
+ if (linkname[0] == '/') {
+ /* Target of symlink is absolute so use it raw. */
+ next_fn = linkname;
+ } else {
+ /* Target of symlink is relative so add to 'fn''s directory. */
+ char *dir = dir_name(fn);
+
+ if (!strcmp(dir, ".")) {
+ next_fn = linkname;
+ } else {
+ char *separator = dir[strlen(dir) - 1] == '/' ? "" : "/";
+ next_fn = xasprintf("%s%s%s", dir, separator, linkname);
+ free(linkname);
+ }
+
+ free(dir);
+ }
+
+ free(fn);
+ fn = next_fn;
+ }
+
+ VLOG_WARN("%s: too many levels of symlinks", filename);
+ free(fn);
+ return xstrdup(filename);
+}