netdev - Re: [RFCv2 bluetooth-next 2/3] ipv6: add ipv6_addr_prefix

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Message-ID: <5655E50C.5090906@osg.samsung.com>
Date:	Wed, 25 Nov 2015 17:42:52 +0100
From:	Stefan Schmidt <stefan@....samsung.com>
To:	Alexander Aring <alex.aring@...il.com>, linux-wpan@...r.kernel.org
Cc:	linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
	kernel@...gutronix.de, mcr@...delman.ca, lukasz.duda@...dicsemi.no,
	martin.gergeleit@...rm.de,
	"David S . Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [RFCv2 bluetooth-next 2/3] ipv6: add ipv6_addr_prefix_cpy

Hello.

On 17/11/15 23:33, Alexander Aring wrote:
> This patch adds a static inline function ipv6_addr_prefix_cpy which
> copies a ipv6 address prefix(argument pfx) into the ipv6 address prefix.
> The prefix len is given by plen as bits. This function mainly based on
> ipv6_addr_prefix which copies one address prefix from address into a new
> ipv6 address destination and zero all other address bits.
>
> The difference is that ipv6_addr_prefix_cpy don't get a prefix from an
> ipv6 address, it sets a prefix to an ipv6 address with keeping other
> address bits. The use case is for context based address compression
> inside 6LoWPAN IPHC header which keeping ipv6 prefixes inside a context
> table to lookup address-bits without sending them.
>
> Cc: David S. Miller<davem@...emloft.net>
> Cc: Alexey Kuznetsov<kuznet@....inr.ac.ru>
> Cc: James Morris<jmorris@...ei.org>
> Cc: Hideaki YOSHIFUJI<yoshfuji@...ux-ipv6.org>
> Cc: Patrick McHardy<kaber@...sh.net>
> Signed-off-by: Alexander Aring<alex.aring@...il.com>
> ---
>   include/net/ipv6.h | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
>
> diff --git a/include/net/ipv6.h b/include/net/ipv6.h
> index e1a10b0..9d38fc2 100644
> --- a/include/net/ipv6.h
> +++ b/include/net/ipv6.h
> @@ -382,6 +382,21 @@ static inline void ipv6_addr_prefix(struct in6_addr *pfx,
>   		pfx->s6_addr[o] = addr->s6_addr[o] & (0xff00 >> b);
>   }
>   
> +static inline void ipv6_addr_prefix_cpy(struct in6_addr *addr,
> +					const struct in6_addr *pfx,
> +					int plen)
> +{

Naming it ipv6_addr_prefix_cop, as Sergei suggested, would be easier to 
read.
> +	/* caller must guarantee 0 <= plen <= 128 */
> +	int o = plen >> 3,
> +	    b = plen & 0x7;
> +

Any reason you are not doing the memset here before memcpy like it is 
done in ipv6_addr_prefi()?
> +	memcpy(addr->s6_addr, pfx, o);
> +	if (b != 0) {
> +		addr->s6_addr[o] &= ~(0xff00 >> b);
> +		addr->s6_addr[o] |= (pfx->s6_addr[o] & (0xff00 >> b));
> +	}
> +}
> +
>   static inline void __ipv6_addr_set_half(__be32 *addr,
>   					__be32 wh, __be32 wl)
>   {

regards
Stefan Schmidt

regards
Stefan Schmidt
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