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Date: Fri, 04 Jan 2013 08:00:19 -0800 From: Eric Dumazet <eric.dumazet@...il.com> To: YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org> Cc: David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org> Subject: Re: [PATCH net-next] ndisc: Remove unused space at tail of skb for ndisc messages. (TAKE 3) On Fri, 2013-01-04 at 22:58 +0900, YOSHIFUJI Hideaki wrote: > Currently, the size of skb allocated for NDISC is MAX_HEADER + > LL_RESERVED_SPACE(dev) + packet length + dev->needed_tailroom, > but only LL_RESERVED_SPACE(dev) bytes is "reserved" for headers. > As a result, the skb looks like this (after construction of the > message): > > head data tail end > +--------------------------------------------------------------+ > + | | | | > +--------------------------------------------------------------+ > |<-hlen---->|<---ipv6 packet------>|<--tlen-->|<--MAX_HEADER-->| > =LL_ = dev > RESERVED_ ->needed_ > SPACE(dev) tailroom > > As the name implies, "MAX_HEADER" is used for headers, and should > be "reserved" in prior to packet construction. Or, if some space > is really required at the tail of ther skb, it should be > explicitly documented. > > We have several option after construction of NDISC message: > > Option 1: > > head data tail end > +---------------------------------------------+ > + | | | > +---------------------------------------------+ > |<-hlen---->|<---ipv6 packet------>|<--tlen-->| > =LL_ = dev > RESERVED_ ->needed_ > SPACE(dev) tailroom Acked-by: Eric Dumazet <edumazet@...gle.com> Thanks ! -- 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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