[PATCH 2/3] VFS: allow MAY_ flags to be easily extended.

From: NeilBrown
Date: Wed Oct 03 2018 - 21:03:37 EST


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@xxxxxxxx>
---
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..b0076cb0f738 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 0x00000100
+
/*
* 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()