Add openat() to compat.

Makefile.am

@@ -238,6 +238,9 @@ endif
 if NO_CFMAKERAW
 nodist_tmux_SOURCES += compat/cfmakeraw.c
 endif
+if NO_OPENAT
+nodist_tmux_SOURCES += compat/openat.c
+endif
 
 # Install tmux.1 in the right format.
 install-exec-hook:

compat.h

@@ -243,7 +243,13 @@ int		 unsetenv(const char *);
 
 #ifndef HAVE_CFMAKERAW
 /* cfmakeraw.c */
-void		cfmakeraw(struct termios *tio);
+void		cfmakeraw(struct termios *);
+#endif
+
+#ifndef HAVE_OPENAT
+/* openat.c */
+#define AT_FDCWD -100
+int		openat(int, const char *, int, ...);
 #endif
 
 #ifdef HAVE_GETOPT

compat/openat.c

@@ -0,0 +1,63 @@
+/* $Id$ */
+
+/*
+ * Copyright (c) 2013 Nicholas Marriott <nicm@users.sourceforge.net>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
+ * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+ * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdarg.h>
+#include <unistd.h>
+
+#include "tmux.h"
+
+int
+openat(int fd, const char *path, int flags, ...)
+{
+	mode_t	mode;
+	va_list ap;
+	int	dotfd, retval, saved_errno;
+
+	if (flags & O_CREAT) {
+		va_start(ap, flags);
+		mode = va_arg(ap, mode_t);
+		va_end(ap);
+	} else
+		mode = 0;
+
+	dotfd = -1;
+	if (fd != AT_FDCWD) {
+		dotfd = open(".", O_RDONLY);
+		if (dotfd == -1)
+			return (-1);
+		if (fchdir(fd) != 0)
+			return (-1);
+	}
+
+	retval = open(path, flags, mode);
+
+	if (dotfd != -1) {
+		if (fchdir(dotfd) != 0) {
+			saved_errno = errno;
+			close(retval);
+			close(dotfd);
+			errno = saved_errno;
+			return (-1);
+		}
+		close(dotfd);
+	}
+
+	return (retval);
+}

configure.ac

@@ -323,6 +323,13 @@ if test "x$found_cfmakeraw" = xyes; then
 fi
 AM_CONDITIONAL(NO_CFMAKERAW, [test "x$found_cfmakeraw" = xno])
 
+# Look for openat, compat/openat.c used if missing.
+AC_CHECK_FUNC(openat, found_openat=yes, found_openat=no)
+if test "x$found_openat" = xyes; then
+	AC_DEFINE(HAVE_OPENAT)
+fi
+AM_CONDITIONAL(NO_OPENAT, [test "x$found_openat" = xno])
+
 # Look for getopt. glibc's getopt does not enforce argument order and the ways
 # of making it do so are stupid, so just use our own instead.
 AC_CHECK_FUNC(getopt, found_getopt=yes, found_getopt=no)