+if (!f.running_in_test_harness && real_uid != root_uid && real_uid != exim_uid) goto cleanup;
+if (pid_len < 2 || pid_len >= (int)sizeof(pid_line)) goto cleanup;
+
+path = CS string_copy(pid_file_path);
+if ((base = Ustrrchr(path, '/')) == NULL) /* should not happen, but who knows */
+ log_write(0, LOG_MAIN|LOG_PANIC_DIE, "pid file path \"%s\" does not contain a '/'", pid_file_path);
+
+dir = (base != path) ? path : "/";
+*base++ = '\0';
+
+if (!dir || !*dir || *dir != '/') goto cleanup;
+if (!base || !*base || strchr(base, '/') != NULL) goto cleanup;
+
+cwd_fd = open(".", dir_flags);
+if (cwd_fd < 0 || fstat(cwd_fd, &sb) != 0 || !S_ISDIR(sb.st_mode)) goto cleanup;
+dir_fd = open(dir, dir_flags);
+if (dir_fd < 0 || fstat(dir_fd, &sb) != 0 || !S_ISDIR(sb.st_mode)) goto cleanup;
+
+/* emulate openat */
+if (fchdir(dir_fd) != 0) goto cleanup;
+base_fd = open(base, O_RDONLY | base_flags);
+if (fchdir(cwd_fd) != 0)
+ log_write(0, LOG_MAIN|LOG_PANIC_DIE, "can't return to previous working dir: %s", strerror(errno));
+
+if (base_fd >= 0)
+ {
+ char line[sizeof(pid_line)];
+ ssize_t len = -1;
+
+ if (fstat(base_fd, &sb) != 0 || !S_ISREG(sb.st_mode)) goto cleanup;
+ if ((sb.st_mode & 07777) != base_mode || sb.st_nlink != 1) goto cleanup;
+ if (sb.st_size < 2 || sb.st_size >= (off_t)sizeof(line)) goto cleanup;
+
+ len = read(base_fd, line, sizeof(line));
+ if (len != (ssize_t)sb.st_size) goto cleanup;
+ line[len] = '\0';
+
+ if (strspn(line, "0123456789") != (size_t)len-1) goto cleanup;
+ if (line[len-1] != '\n') goto cleanup;
+ lines_match = (len == pid_len && strcmp(line, pid_line) == 0);
+ }
+
+if (operation == PID_WRITE)