fcntl: support F_DUPFD_CLOEXEC on systems with fcntl

[gnulib.git] / lib / fcntl.c

diff --git a/lib/fcntl.c b/lib/fcntl.c
new file mode 100644 (file)
index 0000000..3c05d31
--- /dev/null
+++ b/lib/fcntl.c
@@ -0,0 +1,104 @@
+/* Provide file descriptor control.
+
+   Copyright (C) 2009 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 <http://www.gnu.org/licenses/>.  */
+
+/* Written by Eric Blake <ebb9@byu.net>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <fcntl.h>
+
+#include <errno.h>
+#include <stdarg.h>
+
+#if !HAVE_FCNTL
+# error not ported to mingw yet
+#endif
+#undef fcntl
+
+/* Perform the specified ACTION on the file descriptor FD, possibly
+   using the argument ARG further described below.  This replacement
+   handles the following actions, and forwards all others on to the
+   native fcntl.
+
+   F_DUPFD_CLOEXEC - duplicate FD, with int ARG being the minimum
+   target fd.  If successful, return the duplicate, which will not be
+   inheritable; otherwise return -1 and set errno.  */
+
+int
+rpl_fcntl (int fd, int action, /* arg */...)
+{
+  va_list arg;
+  int result = -1;
+  va_start (arg, action);
+  switch (action)
+    {
+    case F_DUPFD_CLOEXEC:
+      {
+        int target = va_arg (arg, int);
+
+        /* Try the system call first, if the headers claim it exists
+           (that is, if GNULIB_defined_F_DUPFD_CLOEXEC is 0), since we
+           may be running with a glibc that has the macro but with an
+           older kernel that does not support it.  Cache the
+           information on whether the system call really works, but
+           avoid caching failure if the corresponding F_DUPFD fails
+           for any reason.  0 = unknown, 1 = yes, -1 = no.  */
+        static int have_dupfd_cloexec = GNULIB_defined_F_DUPFD_CLOEXEC ? -1 : 0;
+        if (0 <= have_dupfd_cloexec)
+          {
+            result = fcntl (fd, action, target);
+            if (0 <= result || errno != EINVAL)
+              have_dupfd_cloexec = 1;
+            else
+              {
+                result = fcntl (fd, F_DUPFD, target);
+                if (result < 0)
+                  break;
+                have_dupfd_cloexec = -1;
+              }
+          }
+        else
+          result = fcntl (fd, F_DUPFD, target);
+        if (0 <= result && have_dupfd_cloexec == -1)
+          {
+            int flags = fcntl (result, F_GETFD);
+            if (flags < 0 || fcntl (result, F_SETFD, flags | FD_CLOEXEC) == -1)
+              {
+                int saved_errno = errno;
+                close (result);
+                errno = saved_errno;
+                result = -1;
+              }
+          }
+#if REPLACE_FCHDIR
+        if (0 <= result)
+          result = _gl_register_dup (fd, result);
+#endif
+        break;
+      } /* F_DUPFD_CLOEXEC */
+
+    default:
+      {
+        void *p = va_arg (arg, void *);
+        result = fcntl (fd, action, p);
+        break;
+      }
+    }
+  va_end (arg);
+  return result;
+}