[PATCH 3/5] vfs: O_* bit numbers uniqueness check

[Wu Fengguang]

The O_* bit numbers are defined in 20+ arch/*, and can silently overlap.
Add a compile time check to ensure the uniqueness as suggested by David
Miller.

v4: use the nice hweight_long() (suggested by Jamie)
    split O_SYNC to (__O_SYNC | O_DSYNC) (suggested by Andreas)
    take away the FMODE_* and O_RANDOM bits
v3: change to BUILD_BUG_ON() (suggested by Roland)

CC: David Miller <davem@xxxxxxxxxxxxx>
CC: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
CC: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
CC: Christoph Hellwig <hch@xxxxxxxxxxxxx>
CC: Eric Paris <eparis@xxxxxxxxxx>
CC: Roland Dreier <rdreier@xxxxxxxxx>
CC: Jamie Lokier <jamie@xxxxxxxxxxxxx>
CC: Andreas Schwab <schwab@xxxxxxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 fs/fcntl.c                  |   14 ++++++++++++--
 include/asm-generic/fcntl.h |    2 ++
 2 files changed, 14 insertions(+), 2 deletions(-)

--- linux-mm.orig/fs/fcntl.c	2010-01-30 17:14:13.000000000 +0800
+++ linux-mm/fs/fcntl.c	2010-01-30 17:41:36.000000000 +0800
@@ -741,11 +741,21 @@ void kill_fasync(struct fasync_struct **
 }
 EXPORT_SYMBOL(kill_fasync);
 
-static int __init fasync_init(void)
+static int __init fcntl_init(void)
 {
+	/* please add new bits here to ensure allocation uniqueness */
+	BUILD_BUG_ON(17 != hweight_long(
+		O_RDONLY	| O_WRONLY	| O_RDWR	|
+		O_CREAT		| O_EXCL	| O_NOCTTY	|
+		O_TRUNC		| O_APPEND	| O_NONBLOCK	|
+		__O_SYNC	| O_DSYNC	| FASYNC	|
+		O_DIRECT	| O_LARGEFILE	| O_DIRECTORY	|
+		O_NOFOLLOW	| O_NOATIME	| O_CLOEXEC
+		));
+
 	fasync_cache = kmem_cache_create("fasync_cache",
 		sizeof(struct fasync_struct), 0, SLAB_PANIC, NULL);
 	return 0;
 }
 
-module_init(fasync_init)
+module_init(fcntl_init)
--- linux-mm.orig/include/asm-generic/fcntl.h	2010-01-30 17:40:48.000000000 +0800
+++ linux-mm/include/asm-generic/fcntl.h	2010-01-30 17:41:36.000000000 +0800
@@ -4,6 +4,8 @@
 #include <linux/types.h>
 
 /*
+ * When introducing new O_* bits, please check its uniqueness in fcntl_init().
+ *
  * FMODE_EXEC is 0x20
  * FMODE_NONOTIFY is 0x1000000
  * These cannot be used by userspace O_* until internal and external open


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