1 files changed, 46 insertions, 0 deletions
diff --git a/lib/fd-reopen.c b/lib/fd-reopen.c
new file mode 100644
index 0000000..9c22f11
--- /dev/null
+++ b/lib/fd-reopen.c
@@ -0,0 +1,46 @@
+/* Invoke open, but return either a desired file descriptor or -1.
+
+   Copyright (C) 2005-2022 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Paul Eggert.  */
+
+#include <config.h>
+
+#include "fd-reopen.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+/* Open a file to a particular file descriptor.  This is like standard
+   'open', except it always returns DESIRED_FD if successful.  */
+
+int
+fd_reopen (int desired_fd, char const *file, int flags, mode_t mode)
+{
+  int fd = open (file, flags, mode);
+
+  if (fd == desired_fd || fd < 0)
+    return fd;
+  else
+    {
+      int fd2 = dup2 (fd, desired_fd);
+      int saved_errno = errno;
+      close (fd);
+      errno = saved_errno;
+      return fd2;
+    }
+}