vfs: O_* bit numbers uniqueness check

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.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: David Miller <davem@davemloft.net>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Eric Paris <eparis@redhat.com>
Cc: Roland Dreier <rdreier@cisco.com>
Cc: Jamie Lokier <jamie@shareable.org>
Cc: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 17 insertions, 2 deletions

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 9d175d623aab..6769fd0f35b8 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -767,11 +767,22 @@ void kill_fasync(struct fasync_struct **fp, int sig, int band)
 }
 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(19 - 1 /* for O_RDONLY being 0 */ != HWEIGHT32(
+                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     |
+                FMODE_EXEC
+                ));
+
         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)
diff --git a/include/asm-generic/fcntl.h b/include/asm-generic/fcntl.h
index e3cbc38bdcc2..a70b2d2bfc14 100644
--- a/include/asm-generic/fcntl.h
+++ b/include/asm-generic/fcntl.h
@@ -11,6 +11,10 @@
  * -Eric Paris
  */
 
+/*
+ * When introducing new O_* bits, please check its uniqueness in fcntl_init().
+ */
+
 #define O_ACCMODE       00000003
 #define O_RDONLY        00000000
 #define O_WRONLY        00000001