Sanitize f_flags helpers

* pull ACC_MODE to fs.h; we have several copies all over the place
* nightmarish expression calculating f_mode by f_flags deserves a helper
too (OPEN_FMODE(flags))

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/fs.h b/include/linux/fs.h
index cca1919..9e13b53 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2464,5 +2464,8 @@
 
 int __init get_filesystem_list(char *buf);
 
+#define ACC_MODE(x) ("\000\004\002\006"[(x)&O_ACCMODE])
+#define OPEN_FMODE(flag) ((__force fmode_t)((flag + 1) & O_ACCMODE))
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_FS_H */