fs: O_* bit numbers uniqueness check
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From: Roland Dreier on 6 Jan 2010 02:10 > + /* 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. -- 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: Eric Dumazet on 6 Jan 2010 02:20 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 <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 ? -- 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 6 Jan 2010 02:30 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.. Thanks, Fengguang -- 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: Roland Dreier on 6 Jan 2010 02:40 > 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. -- 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 6 Jan 2010 02:50
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 <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> CC: Roland Dreier <rdreier(a)cisco.com> Signed-off-by: Wu Fengguang <fengguang.wu(a)intel.com> --- 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 /* -- 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/ |