The O_* bit numbers are defined in 20+ arch/*, and hence can silently
overlap. Add a boot time check to ensure the uniqueness as suggested
by David Miller.
CC: David Miller <[email protected]>
CC: Stephen Rothwell <[email protected]>
CC: Al Viro <[email protected]>
CC: Christoph Hellwig <[email protected]>
CC: Eric Paris <[email protected]>
Signed-off-by: Wu Fengguang <[email protected]>
---
fs/fcntl.c | 14 ++++++++++++--
include/asm-generic/fcntl.h | 2 ++
2 files changed, 14 insertions(+), 2 deletions(-)
--- linux.orig/fs/fcntl.c 2010-01-06 14:41:26.000000000 +0800
+++ linux/fs/fcntl.c 2010-01-06 14:46:57.000000000 +0800
@@ -709,11 +709,21 @@ 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 */
+ BUG_ON(20 != hweight32(
+ O_RDONLY | O_WRONLY | O_RDWR |
+ O_CREAT | O_EXCL | O_NOCTTY |
+ O_TRUNC | O_APPEND | O_NONBLOCK |
+ O_SYNC | FASYNC | O_DIRECT |
+ O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW |
+ O_NOATIME | O_CLOEXEC | O_RANDOM |
+ FMODE_EXEC | FMODE_NONOTIFY));
+
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.orig/include/asm-generic/fcntl.h 2010-01-06 14:45:34.000000000 +0800
+++ linux/include/asm-generic/fcntl.h 2010-01-06 14:50:57.000000000 +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
> + /* please add new bits here to ensure allocation uniqueness */
> + BUG_ON(20 != hweight32(
> + O_RDONLY | O_WRONLY | O_RDWR |
I wonder if there's a way to make this BUILD_BUG_ON(), so the problem is
caught at compile time (a change like adding an O_ flag is often compile
tested only for obscure archs). One could create a compile-time
macro-ized version of hweight32() and use that, I guess, although I'm
not sure it's worth the ugliness.
Failing that maybe this should be WARN_ON()? I'd be annoyed if my arch
wouldn't boot because some strange new O_ flag happened to collide.
- R.
Le 06/01/2010 07:55, Wu Fengguang a ?crit :
> The O_* bit numbers are defined in 20+ arch/*, and hence can silently
> overlap. Add a boot time check to ensure the uniqueness as suggested
> by David Miller.
>
> CC: David Miller <[email protected]>
> CC: Stephen Rothwell <[email protected]>
> CC: Al Viro <[email protected]>
> CC: Christoph Hellwig <[email protected]>
> CC: Eric Paris <[email protected]>
> Signed-off-by: Wu Fengguang <[email protected]>
> ---
> {
> + /* please add new bits here to ensure allocation uniqueness */
> + BUG_ON(20 != hweight32(
> + O_RDONLY | O_WRONLY | O_RDWR |
> + O_CREAT | O_EXCL | O_NOCTTY |
> + O_TRUNC | O_APPEND | O_NONBLOCK |
> + O_SYNC | FASYNC | O_DIRECT |
> + O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW |
> + O_NOATIME | O_CLOEXEC | O_RANDOM |
> + FMODE_EXEC | FMODE_NONOTIFY));
> +
I cannot test it, but given O_RDONLY is 0, are you sure 20 bits are actually set ?
On Wed, Jan 06, 2010 at 03:08:08PM +0800, Roland Dreier wrote:
>
> > + /* please add new bits here to ensure allocation uniqueness */
> > + BUG_ON(20 != hweight32(
> > + O_RDONLY | O_WRONLY | O_RDWR |
>
> I wonder if there's a way to make this BUILD_BUG_ON(), so the problem is
> caught at compile time (a change like adding an O_ flag is often compile
> tested only for obscure archs). One could create a compile-time
> macro-ized version of hweight32() and use that, I guess, although I'm
> not sure it's worth the ugliness.
Yeah, I chose the boot time check because of hweight32()..
> Failing that maybe this should be WARN_ON()? I'd be annoyed if my arch
> wouldn't boot because some strange new O_ flag happened to collide.
Good suggestion! Here is the updated patch.
Andrew, this patch relies on the newly introduced O_RANDOM and Eric's
FMODE_NONOTIFY.
Thanks,
Fengguang
---
fs: O_* bit numbers uniqueness check
The O_* bit numbers are defined in 20+ arch/*, and hence can silently
overlap. Add a boot time check to ensure the uniqueness as suggested
by David Miller.
v2: change to WARN_ON() as suggested by Roland
CC: David Miller <[email protected]>
CC: Stephen Rothwell <[email protected]>
CC: Al Viro <[email protected]>
CC: Christoph Hellwig <[email protected]>
CC: Eric Paris <[email protected]>
CC: Roland Dreier <[email protected]>
Signed-off-by: Wu Fengguang <[email protected]>
---
fs/fcntl.c | 14 ++++++++++++--
include/asm-generic/fcntl.h | 2 ++
2 files changed, 14 insertions(+), 2 deletions(-)
--- linux.orig/fs/fcntl.c 2010-01-06 14:41:26.000000000 +0800
+++ linux/fs/fcntl.c 2010-01-06 15:15:11.000000000 +0800
@@ -709,11 +709,21 @@ 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 */
+ WARN_ON(20 != hweight32(
+ O_RDONLY | O_WRONLY | O_RDWR |
+ O_CREAT | O_EXCL | O_NOCTTY |
+ O_TRUNC | O_APPEND | O_NONBLOCK |
+ O_SYNC | FASYNC | O_DIRECT |
+ O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW |
+ O_NOATIME | O_CLOEXEC | O_RANDOM |
+ FMODE_EXEC | FMODE_NONOTIFY));
+
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.orig/include/asm-generic/fcntl.h 2010-01-06 14:45:34.000000000 +0800
+++ linux/include/asm-generic/fcntl.h 2010-01-06 14:50:57.000000000 +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
On Wed, Jan 06, 2010 at 03:07:01PM +0800, Eric Dumazet wrote:
> Le 06/01/2010 07:55, Wu Fengguang a écrit :
> > The O_* bit numbers are defined in 20+ arch/*, and hence can silently
> > overlap. Add a boot time check to ensure the uniqueness as suggested
> > by David Miller.
> >
> > CC: David Miller <[email protected]>
> > CC: Stephen Rothwell <[email protected]>
> > CC: Al Viro <[email protected]>
> > CC: Christoph Hellwig <[email protected]>
> > CC: Eric Paris <[email protected]>
> > Signed-off-by: Wu Fengguang <[email protected]>
> > ---
> > {
> > + /* please add new bits here to ensure allocation uniqueness */
> > + BUG_ON(20 != hweight32(
> > + O_RDONLY | O_WRONLY | O_RDWR |
> > + O_CREAT | O_EXCL | O_NOCTTY |
> > + O_TRUNC | O_APPEND | O_NONBLOCK |
> > + O_SYNC | FASYNC | O_DIRECT |
> > + O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW |
> > + O_NOATIME | O_CLOEXEC | O_RANDOM |
> > + FMODE_EXEC | FMODE_NONOTIFY));
> > +
>
> I cannot test it, but given O_RDONLY is 0, are you sure 20 bits are actually set ?
Yes, I tested it. The tricky one is O_SYNC, which actually has two bits..
Thanks,
Fengguang
> Yeah, I chose the boot time check because of hweight32()..
One could do something like
#define HWEIGHT32(x) (!!((x) & (1u << 0)) +
!!((x) & (1u << 1)) +
//...
!!((x) & (1u << 31)));
that would probably work with BUILD_BUG_ON().
But as I said maybe it's too ugly.
- R.
On Wed, Jan 06, 2010 at 03:30:31PM +0800, Roland Dreier wrote:
>
> > Yeah, I chose the boot time check because of hweight32()..
>
> One could do something like
>
> #define HWEIGHT32(x) (!!((x) & (1u << 0)) +
> !!((x) & (1u << 1)) +
> //...
> !!((x) & (1u << 31)));
>
> that would probably work with BUILD_BUG_ON().
>
> But as I said maybe it's too ugly.
Yes, it'll feel like this. Then you'll have to fix the possible error
in order to compile ;)
---
fs: O_* bit numbers uniqueness check
The O_* bit numbers are defined in 20+ arch/*, and hence can silently
overlap. Add a boot time check to ensure the uniqueness as suggested
by David Miller.
v3: change to BUILD_BUG_ON() as suggested by Roland
CC: David Miller <[email protected]>
CC: Stephen Rothwell <[email protected]>
CC: Al Viro <[email protected]>
CC: Christoph Hellwig <[email protected]>
CC: Eric Paris <[email protected]>
CC: Roland Dreier <[email protected]>
Signed-off-by: Wu Fengguang <[email protected]>
---
fs/fcntl.c | 14 ++++++++++++--
include/asm-generic/fcntl.h | 2 ++
include/linux/bitops.h | 33 +++++++++++++++++++++++++++++++++
3 files changed, 47 insertions(+), 2 deletions(-)
--- linux.orig/fs/fcntl.c 2010-01-06 14:41:26.000000000 +0800
+++ linux/fs/fcntl.c 2010-01-06 15:37:14.000000000 +0800
@@ -709,11 +709,21 @@ 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(20 != HWEIGHT32(
+ O_RDONLY | O_WRONLY | O_RDWR |
+ O_CREAT | O_EXCL | O_NOCTTY |
+ O_TRUNC | O_APPEND | O_NONBLOCK |
+ O_SYNC | FASYNC | O_DIRECT |
+ O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW |
+ O_NOATIME | O_CLOEXEC | O_RANDOM |
+ FMODE_EXEC | FMODE_NONOTIFY));
+
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.orig/include/asm-generic/fcntl.h 2010-01-06 14:45:34.000000000 +0800
+++ linux/include/asm-generic/fcntl.h 2010-01-06 14:50:57.000000000 +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
--- linux.orig/include/linux/bitops.h 2010-01-06 15:33:39.000000000 +0800
+++ linux/include/linux/bitops.h 2010-01-06 15:38:57.000000000 +0800
@@ -8,6 +8,39 @@
#define BIT_WORD(nr) ((nr) / BITS_PER_LONG)
#define BITS_PER_BYTE 8
#define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
+
+#define HWEIGHT32(x) (!!((x) & (1u << 0)) + \
+ !!((x) & (1u << 1)) + \
+ !!((x) & (1u << 2)) + \
+ !!((x) & (1u << 3)) + \
+ !!((x) & (1u << 4)) + \
+ !!((x) & (1u << 5)) + \
+ !!((x) & (1u << 6)) + \
+ !!((x) & (1u << 7)) + \
+ !!((x) & (1u << 8)) + \
+ !!((x) & (1u << 9)) + \
+ !!((x) & (1u << 10)) + \
+ !!((x) & (1u << 11)) + \
+ !!((x) & (1u << 12)) + \
+ !!((x) & (1u << 13)) + \
+ !!((x) & (1u << 14)) + \
+ !!((x) & (1u << 15)) + \
+ !!((x) & (1u << 16)) + \
+ !!((x) & (1u << 17)) + \
+ !!((x) & (1u << 18)) + \
+ !!((x) & (1u << 19)) + \
+ !!((x) & (1u << 20)) + \
+ !!((x) & (1u << 21)) + \
+ !!((x) & (1u << 22)) + \
+ !!((x) & (1u << 23)) + \
+ !!((x) & (1u << 24)) + \
+ !!((x) & (1u << 25)) + \
+ !!((x) & (1u << 26)) + \
+ !!((x) & (1u << 27)) + \
+ !!((x) & (1u << 28)) + \
+ !!((x) & (1u << 29)) + \
+ !!((x) & (1u << 30)) + \
+ !!((x) & (1u << 31)))
#endif
/*
On Wed, Jan 06, 2010 at 02:55:26PM +0800, Wu Fengguang wrote:
> The O_* bit numbers are defined in 20+ arch/*, and hence can silently
> overlap. Add a boot time check to ensure the uniqueness as suggested
> by David Miller.
The right fix is to stop overlyaing the FMODE_ flags into the O_
namespace. Al has been working towards this.
Roland Dreier wrote:
>
> > + /* please add new bits here to ensure allocation uniqueness */
> > + BUG_ON(20 != hweight32(
> > + O_RDONLY | O_WRONLY | O_RDWR |
>
> I wonder if there's a way to make this BUILD_BUG_ON(), so the problem is
> caught at compile time (a change like adding an O_ flag is often compile
> tested only for obscure archs). One could create a compile-time
> macro-ized version of hweight32() and use that, I guess, although I'm
> not sure it's worth the ugliness.
Not ugly at all:
#define hweight32(x) __builtin_popcount(x)
Checked GCC 3.4.3 / 4.1 / 4.4: It expands as a compile-time constant
if the argument is a compile-time constant, so can be used in
BUILD_BUG_ON() and even for array sizes etc.
If GCC's __builtin_popcount() isn't good enough for non-constant
values, the macro would be more involved:
#define hweight32(x) (__builtin_constant_p(x) ? __builtin_popcount(x) \
: hweight32_nonconstant(x))
-- Jamie
Wu Fengguang <[email protected]> writes:
> On Wed, Jan 06, 2010 at 03:07:01PM +0800, Eric Dumazet wrote:
>> Le 06/01/2010 07:55, Wu Fengguang a écrit :
>> > The O_* bit numbers are defined in 20+ arch/*, and hence can silently
>> > overlap. Add a boot time check to ensure the uniqueness as suggested
>> > by David Miller.
>> >
>> > CC: David Miller <[email protected]>
>> > CC: Stephen Rothwell <[email protected]>
>> > CC: Al Viro <[email protected]>
>> > CC: Christoph Hellwig <[email protected]>
>> > CC: Eric Paris <[email protected]>
>> > Signed-off-by: Wu Fengguang <[email protected]>
>> > ---
>> > {
>> > + /* please add new bits here to ensure allocation uniqueness */
>> > + BUG_ON(20 != hweight32(
>> > + O_RDONLY | O_WRONLY | O_RDWR |
>> > + O_CREAT | O_EXCL | O_NOCTTY |
>> > + O_TRUNC | O_APPEND | O_NONBLOCK |
>> > + O_SYNC | FASYNC | O_DIRECT |
>> > + O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW |
>> > + O_NOATIME | O_CLOEXEC | O_RANDOM |
>> > + FMODE_EXEC | FMODE_NONOTIFY));
>> > +
>>
>> I cannot test it, but given O_RDONLY is 0, are you sure 20 bits are actually set ?
>
> Yes, I tested it. The tricky one is O_SYNC, which actually has two bits..
What if a new architecture wants to use a single bit value (since it
does not need backwards compatibility)?
Andreas.
--
Andreas Schwab, [email protected]
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
On Wed, Jan 06, 2010 at 05:13:54PM +0800, Andreas Schwab wrote:
> Wu Fengguang <[email protected]> writes:
>
> > On Wed, Jan 06, 2010 at 03:07:01PM +0800, Eric Dumazet wrote:
> >> Le 06/01/2010 07:55, Wu Fengguang a écrit :
> >> > The O_* bit numbers are defined in 20+ arch/*, and hence can silently
> >> > overlap. Add a boot time check to ensure the uniqueness as suggested
> >> > by David Miller.
> >> >
> >> > CC: David Miller <[email protected]>
> >> > CC: Stephen Rothwell <[email protected]>
> >> > CC: Al Viro <[email protected]>
> >> > CC: Christoph Hellwig <[email protected]>
> >> > CC: Eric Paris <[email protected]>
> >> > Signed-off-by: Wu Fengguang <[email protected]>
> >> > ---
> >> > {
> >> > + /* please add new bits here to ensure allocation uniqueness */
> >> > + BUG_ON(20 != hweight32(
> >> > + O_RDONLY | O_WRONLY | O_RDWR |
> >> > + O_CREAT | O_EXCL | O_NOCTTY |
> >> > + O_TRUNC | O_APPEND | O_NONBLOCK |
> >> > + O_SYNC | FASYNC | O_DIRECT |
> >> > + O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW |
> >> > + O_NOATIME | O_CLOEXEC | O_RANDOM |
> >> > + FMODE_EXEC | FMODE_NONOTIFY));
> >> > +
> >>
> >> I cannot test it, but given O_RDONLY is 0, are you sure 20 bits are actually set ?
> >
> > Yes, I tested it. The tricky one is O_SYNC, which actually has two bits..
>
> What if a new architecture wants to use a single bit value (since it
> does not need backwards compatibility)?
You mean to test __O_SYNC | O_DSYNC instead of O_SYNC?
On Thu, Jan 07, 2010 at 12:20:04AM +0800, Jamie Lokier wrote:
> Roland Dreier wrote:
> >
> > > + /* please add new bits here to ensure allocation uniqueness */
> > > + BUG_ON(20 != hweight32(
> > > + O_RDONLY | O_WRONLY | O_RDWR |
> >
> > I wonder if there's a way to make this BUILD_BUG_ON(), so the problem is
> > caught at compile time (a change like adding an O_ flag is often compile
> > tested only for obscure archs). One could create a compile-time
> > macro-ized version of hweight32() and use that, I guess, although I'm
> > not sure it's worth the ugliness.
>
> Not ugly at all:
>
> #define hweight32(x) __builtin_popcount(x)
>
> Checked GCC 3.4.3 / 4.1 / 4.4: It expands as a compile-time constant
> if the argument is a compile-time constant, so can be used in
> BUILD_BUG_ON() and even for array sizes etc.
>
> If GCC's __builtin_popcount() isn't good enough for non-constant
> values, the macro would be more involved:
>
> #define hweight32(x) (__builtin_constant_p(x) ? __builtin_popcount(x) \
> : hweight32_nonconstant(x))
Jamie, Thanks for the hint! Would you sign this patch?
---
bitops: compile time optimization for hweight_long(CONSTANT)
This allows use of hweight_long() in BUILD_BUG_ON().
Suggested by Jamie.
CC: Jamie Lokier <[email protected]>
CC: Roland Dreier <[email protected]>
Signed-off-by: Wu Fengguang <[email protected]>
---
include/linux/bitops.h | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
--- linux.orig/include/linux/bitops.h 2010-01-09 12:13:00.000000000 +0800
+++ linux/include/linux/bitops.h 2010-01-09 12:21:50.000000000 +0800
@@ -40,10 +40,14 @@ static __inline__ int get_count_order(un
return order;
}
-static inline unsigned long hweight_long(unsigned long w)
-{
- return sizeof(w) == 4 ? hweight32(w) : hweight64(w);
-}
+#define hweight_long(x) \
+( \
+ __builtin_constant_p(x) ? \
+ __builtin_popcountl(x) : \
+ (sizeof(x) <= 4 ? \
+ hweight32(x) : \
+ hweight64(x)) \
+)
/**
* rol32 - rotate a 32-bit value left
On Wed, Jan 06, 2010 at 11:48:14PM +0800, Christoph Hellwig wrote:
> On Wed, Jan 06, 2010 at 02:55:26PM +0800, Wu Fengguang wrote:
> > The O_* bit numbers are defined in 20+ arch/*, and hence can silently
> > overlap. Add a boot time check to ensure the uniqueness as suggested
> > by David Miller.
>
> The right fix is to stop overlyaing the FMODE_ flags into the O_
> namespace. Al has been working towards this.
I thinks they are orthogonal problems -- this patch watches for the
possible conflicting O_* in so many archs.
Anyway here is the new version without the FMODE_ and O_RANDOM.
Thanks,
Fengguang
---
fs: O_* bit numbers uniqueness check
The O_* bit numbers are defined in 20+ arch/*, and hence can silently
overlap. Add a boot time check to ensure the uniqueness as suggested
by David Miller.
v4: use the nice hweight_long() as suggested by Jamie
split O_SYNC to (__O_SYNC | O_DSYNC) as suggested by Andreas
take away FMODE_* and O_RANDOM
v3: change to BUILD_BUG_ON() as suggested by Roland
CC: David Miller <[email protected]>
CC: Stephen Rothwell <[email protected]>
CC: Al Viro <[email protected]>
CC: Christoph Hellwig <[email protected]>
CC: Eric Paris <[email protected]>
CC: Roland Dreier <[email protected]>
CC: Jamie Lokier <[email protected]>
CC: Andreas Schwab <[email protected]>
Signed-off-by: Wu Fengguang <[email protected]>
---
fs/fcntl.c | 14 ++++++++++++--
include/asm-generic/fcntl.h | 2 ++
2 files changed, 14 insertions(+), 2 deletions(-)
--- linux.orig/fs/fcntl.c 2010-01-09 11:02:57.000000000 +0800
+++ linux/fs/fcntl.c 2010-01-09 21:36:16.000000000 +0800
@@ -709,11 +709,21 @@ 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.orig/include/asm-generic/fcntl.h 2010-01-09 11:02:57.000000000 +0800
+++ linux/include/asm-generic/fcntl.h 2010-01-09 12:23:17.000000000 +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