NFSD uses permission flags similar to the MAY_* flags,
with some overlap, and depends on the overlap matching.
This is currently a little fragile and hard to extend.

So add __MAY_UNUSED to identify the first unused flag,
and have NFSD use that flag and later flags for its
non-standard permissions.

Signed-off-by: NeilBrown <neilb@suse.com>
---

v1 of this patch had an obvious bug which, of course, I couldn't see
until after posting.
__MAY_UNUSED had the same value as MAY_ACT_AS_OWNER - so it wasn't
unused!

NeilBrown


 fs/nfsd/vfs.h      | 33 ++++++++++++++++++---------------
 include/linux/fs.h |  2 ++
 2 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
index a7e107309f76..2b1c70d3757a 100644
--- a/fs/nfsd/vfs.h
+++ b/fs/nfsd/vfs.h
@@ -13,23 +13,26 @@
  * Flags for nfsd_permission
  */
 #define NFSD_MAY_NOP			0
-#define NFSD_MAY_EXEC			0x001 /* == MAY_EXEC */
-#define NFSD_MAY_WRITE			0x002 /* == MAY_WRITE */
-#define NFSD_MAY_READ			0x004 /* == MAY_READ */
-#define NFSD_MAY_SATTR			0x008
-#define NFSD_MAY_TRUNC			0x010
-#define NFSD_MAY_LOCK			0x020
-#define NFSD_MAY_MASK			0x03f
+#define NFSD_MAY_EXEC			MAY_EXEC
+#define NFSD_MAY_WRITE			MAY_WRITE
+#define NFSD_MAY_READ			MAY_READ
+#define NFSD_MAY_SATTR			(__MAY_UNUSED << 0)
+#define NFSD_MAY_TRUNC			(__MAY_UNUSED << 1)
+#define NFSD_MAY_LOCK			(__MAY_UNUSED << 2)
+#define __NFSD_MAY_FIRST_HINT		(__MAY_UNUSED << 3)
+#define NFSD_MAY_MASK			(__NFSD_MAY_FIRST_HINT - 1)
 
 /* extra hints to permission and open routines: */
-#define NFSD_MAY_OWNER_OVERRIDE		0x040
-#define NFSD_MAY_LOCAL_ACCESS		0x080 /* for device special files */
-#define NFSD_MAY_BYPASS_GSS_ON_ROOT	0x100
-#define NFSD_MAY_NOT_BREAK_LEASE	0x200
-#define NFSD_MAY_BYPASS_GSS		0x400
-#define NFSD_MAY_READ_IF_EXEC		0x800
-
-#define NFSD_MAY_64BIT_COOKIE		0x1000 /* 64 bit readdir cookies for >= NFSv3 */
+#define NFSD_MAY_OWNER_OVERRIDE		(__NFSD_MAY_FIRST_HINT << 0)
+/* for device special files */
+#define NFSD_MAY_LOCAL_ACCESS		(__NFSD_MAY_FIRST_HINT << 1)
+#define NFSD_MAY_BYPASS_GSS_ON_ROOT	(__NFSD_MAY_FIRST_HINT << 2)
+#define NFSD_MAY_NOT_BREAK_LEASE	(__NFSD_MAY_FIRST_HINT << 3)
+#define NFSD_MAY_BYPASS_GSS		(__NFSD_MAY_FIRST_HINT << 4)
+#define NFSD_MAY_READ_IF_EXEC		(__NFSD_MAY_FIRST_HINT << 5)
+
+/* 64 bit readdir cookies for >= NFSv3 */
+#define NFSD_MAY_64BIT_COOKIE		(__NFSD_MAY_FIRST_HINT << 6)
 
 #define NFSD_MAY_CREATE		(NFSD_MAY_EXEC|NFSD_MAY_WRITE)
 #define NFSD_MAY_REMOVE		(NFSD_MAY_EXEC|NFSD_MAY_WRITE|NFSD_MAY_TRUNC)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 5a8878a88cbb..9fc914c259f9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -103,6 +103,8 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
  */
 #define MAY_ACT_AS_OWNER	0x00000100
 
+#define	__MAY_UNUSED		0x00000200
+
 /*
  * flags in file.f_mode.  Note that FMODE_READ and FMODE_WRITE must correspond
  * to O_WRONLY and O_RDWR via the strange trick in do_dentry_open()
-- 
2.14.0.rc0.dirty