netdev - RE: [PATCH 02/05] ipv6: RFC4214 Support

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Date:	Wed, 7 Nov 2007 10:24:50 -0800
From:	"Templin, Fred L" <Fred.L.Templin@...ing.com>
To:	YOSHIFUJI Hideaki / 吉藤英明 
	<yoshfuji@...ux-ipv6.org>, <netdev@...eo.de>
Cc:	<netdev@...r.kernel.org>
Subject: RE: [PATCH 02/05] ipv6: RFC4214 Support

 

> -----Original Message-----
> From: YOSHIFUJI Hideaki / 吉藤英明 [mailto:yoshfuji@...ux-ipv6.org] 
> Sent: Wednesday, November 07, 2007 10:12 AM
> To: netdev@...eo.de
> Cc: Templin, Fred L; netdev@...r.kernel.org; yoshfuji@...ux-ipv6.org
> Subject: Re: [PATCH 02/05] ipv6: RFC4214 Support
> 
> Hello.
> 
> In article <200711071658.59478.netdev@...eo.de> (at Wed, 7 
> Nov 2007 16:58:59 +0100), Ingo Oeser <netdev@...eo.de> says:
> 
> > > +	eui[0] = 0;
> > > +
> > > +	/* Check for RFC3330 global address ranges */
> > > +	if (((ipv4 >= 0x01000000) && (ipv4 < 0x0a000000)) ||
> > > +	    ((ipv4 >= 0x0b000000) && (ipv4 < 0x7f000000)) ||
> > > +	    ((ipv4 >= 0x80000000) && (ipv4 < 0xa9fe0000)) ||
> > > +	    ((ipv4 >= 0xa9ff0000) && (ipv4 < 0xac100000)) ||
> > > +	    ((ipv4 >= 0xac200000) && (ipv4 < 0xc0a80000)) ||
> > > +	    ((ipv4 >= 0xc0a90000) && (ipv4 < 0xc6120000)) ||
> > > +	    ((ipv4 >= 0xc6140000) && (ipv4 < 0xe0000000))) eui[0] |=
> > > 0x2;
> > > +
> > 
> > Instead of converting network to host byte order at runtime 
> > and comparing the results to constants, let the compiler convert
> > the constants to network byte order and compare in network order.
> > 
> > so use:
> > 
> >  if (((*addr >= htonl(0x01000000)) && (*addr < 
> htonl(0x0a000000))) || ....
> > 
> > instead. The compiler will notice that "0x01000000" is a 
> constant and will
> > use "_constant_htonl()" automatically.
> 
> No, you cannot do this.
> When you check the "range", you need to use host-byte order.

I think the original poster was correct on this one; the addr comes
in in network byte order, and the constants are depicted in host
byte order. So, the suggested fix was to have htonl(const) to make
all of the constants into network byte order while leaving addr
alone.

> > > +
> > > +static inline int ipv6_addr_is_isatap(const struct 
> in6_addr *addr)
> > > +{
> > > +       return (addr->s6_addr32[2] == 
> __constant_htonl(0x02005EFE) ||
> > > +               addr->s6_addr32[2] == 
> __constant_htonl(0x00005EFE));
> > > +}
> > > +#endif
> > 
> > The compiler will notice that "0x01000000" is a constant and will
> > use "_constant_htonl()" automatically. Please use simply htonl().
> 
> Right.  And, maybe, you can write as follows:
> 	return ((addr->s6_addr32[2] | htonl(0x02000000)) == htonl(0x02005EFE));

This looks good, and the change will be made.

Fred
fred.l.templin@...ing.com

> 
> --yoshfuji
> -
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