fchmodat: fix handling of flags

The Linux syscall takes 3 args, not 4.  We have to process flags in
userspace ourselves.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

libc/sysdeps/linux/common/fchmodat.c

@@ -2,15 +2,36 @@
  * fchmodat() for uClibc
  *
  * Copyright (C) 2009 Analog Devices Inc.
+ * Copyright (C) 2012 Mike Frysinger
  *
  * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
  */
 
+#include <fcntl.h>
 #include <sys/syscall.h>
 #include <sys/stat.h>
 
 #ifdef __NR_fchmodat
-_syscall4(int, fchmodat, int, fd, const char *, file, mode_t, mode, int, flag)
+/*
+ * The kernel takes 3 args, but userland takes 4.
+ * We have to process all the flags ourselves.
+ */
+int fchmodat(int fd, const char *file, mode_t mode, int flag)
+{
+	/* We only support one flag atm ... */
+	if (flag & ~AT_SYMLINK_NOFOLLOW) {
+		__set_errno(EINVAL);
+		return -1;
+	}
+
+	/* ... but Linux doesn't support perms on symlinks. */
+	if (flag & AT_SYMLINK_NOFOLLOW) {
+		__set_errno(ENOTSUP);
+		return -1;
+	}
+
+	return INLINE_SYSCALL(fchmodat, 3, fd, file, mode);
+}
 #else
 /* should add emulation with fchmod() and /proc/self/fd/ ... */
 #endif