fs: O_* bit numbers uniqueness check
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From: Christoph Hellwig on 6 Jan 2010 10:50 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Jamie Lokier on 6 Jan 2010 11:30 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Andreas Schwab on 9 Jan 2010 07:40 Wu Fengguang <fengguang.wu(a)intel.com> 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 <davem(a)davemloft.net> >> > CC: Stephen Rothwell <sfr(a)canb.auug.org.au> >> > CC: Al Viro <viro(a)zeniv.linux.org.uk> >> > CC: Christoph Hellwig <hch(a)infradead.org> >> > CC: Eric Paris <eparis(a)redhat.com> >> > Signed-off-by: Wu Fengguang <fengguang.wu(a)intel.com> >> > --- >> > { >> > + /* 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, schwab(a)linux-m68k.org GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 "And now for something completely different." -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Wu Fengguang on 9 Jan 2010 08:40 On Wed, Jan 06, 2010 at 05:13:54PM +0800, Andreas Schwab wrote: > Wu Fengguang <fengguang.wu(a)intel.com> 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 <davem(a)davemloft.net> > >> > CC: Stephen Rothwell <sfr(a)canb.auug.org.au> > >> > CC: Al Viro <viro(a)zeniv.linux.org.uk> > >> > CC: Christoph Hellwig <hch(a)infradead.org> > >> > CC: Eric Paris <eparis(a)redhat.com> > >> > Signed-off-by: Wu Fengguang <fengguang.wu(a)intel.com> > >> > --- > >> > { > >> > + /* 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? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Wu Fengguang on 9 Jan 2010 08:50
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 <jamie(a)shareable.org> CC: Roland Dreier <rdreier(a)cisco.com> Signed-off-by: Wu Fengguang <fengguang.wu(a)intel.com> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |