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Date: Thu, 22 Nov 2007 20:11:55 -0800 From: Stephen Hemminger <shemminger@...ux-foundation.org> To: Daniel Drake <dsd@...too.org> Cc: davem@...emloft.net, netdev@...r.kernel.org Subject: Re: [PATCH] add compare_ether_addr_unaligned On Fri, 23 Nov 2007 00:09:22 +0000 (GMT) Daniel Drake <dsd@...too.org> wrote: > David Miller found a problem in a wireless driver where I was using > compare_ether_addr() on potentially unaligned data. Document that > compare_ether_addr() is not safe for use everywhere, and add an equivalent > function that works regardless of alignment. > > Signed-off-by: Daniel Drake <dsd@...too.org> > > Index: linux-2.6.24-rc3-git1/include/linux/etherdevice.h > =================================================================== > --- linux-2.6.24-rc3-git1.orig/include/linux/etherdevice.h > +++ linux-2.6.24-rc3-git1/include/linux/etherdevice.h > @@ -123,11 +123,13 @@ static inline void random_ether_addr(u8 > } > > /** > - * compare_ether_addr - Compare two Ethernet addresses > + * compare_ether_addr - Compare two 16-bit-aligned Ethernet addresses > * @addr1: Pointer to a six-byte array containing the Ethernet address > * @addr2: Pointer other six-byte array containing the Ethernet address > * > - * Compare two ethernet addresses, returns 0 if equal > + * Compare two ethernet addresses, returns 0 if equal. Both addresses must > + * be 16-bit aligned. For unaligned or potentially unaligned address > + * comparisons, use compare_ether_addr_unaligned() instead. > */ > static inline unsigned compare_ether_addr(const u8 *addr1, const u8 *addr2) > { > @@ -137,6 +139,21 @@ static inline unsigned compare_ether_add > BUILD_BUG_ON(ETH_ALEN != 6); > return ((a[0] ^ b[0]) | (a[1] ^ b[1]) | (a[2] ^ b[2])) != 0; > } > + > +/** > + * compare_ether_addr_unaligned - Compare two Ethernet addresses > + * @addr1: Pointer to a six-byte array containing the Ethernet address > + * @addr2: Pointer other six-byte array containing the Ethernet address > + * > + * Compare two ethernet addresses, returns 0 if equal. compare_ether_addr() > + * is faster than this function, but unless you can ensure alignment you > + * must use this function instead. > + */ > +static inline unsigned compare_ether_addr_unaligned(const u8 *addr1, > + const u8 *addr2) > +{ > + return memcmp(addr1, addr2, ETH_ALEN); > +} > #endif /* __KERNEL__ */ You could probably get the similar speedup by doing xor by byte, rather than falling back to memcmp. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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