| Message ID | 50E6DFEC.7080603@linux-ipv6.org |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
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@google.com> Thanks ! -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Eric Dumazet <eric.dumazet@gmail.com> Date: Fri, 04 Jan 2013 08:00:19 -0800 > 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@google.com> Applied, thanks for your persistence. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c index 6574175..4c4ccf7 100644 --- a/net/ipv6/ndisc.c +++ b/net/ipv6/ndisc.c @@ -395,7 +395,7 @@ static struct sk_buff *ndisc_build_skb(struct net_device *dev, len += ndisc_opt_addr_space(dev); skb = sock_alloc_send_skb(sk, - (MAX_HEADER + sizeof(struct ipv6hdr) + + (sizeof(struct ipv6hdr) + len + hlen + tlen), 1, &err); if (!skb) { @@ -1439,7 +1439,7 @@ void ndisc_send_redirect(struct sk_buff *skb, const struct in6_addr *target) hlen = LL_RESERVED_SPACE(dev); tlen = dev->needed_tailroom; buff = sock_alloc_send_skb(sk, - (MAX_HEADER + sizeof(struct ipv6hdr) + + (sizeof(struct ipv6hdr) + len + hlen + tlen), 1, &err); if (buff == NULL) {
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 Option 2: head data tail end +--------------------------------------------------+ + | | | +--------------------------------------------------+ |<--MAX_HEADER-->|<---ipv6 packet------>|<--tlen-->| = dev ->needed_ tailroom Option 3: head data tail end +--------------------------------------------------------------+ + | | | | +--------------------------------------------------------------+ |<--MAX_HEADER-->|<-hlen---->|<---ipv6 packet------>|<--tlen-->| =LL_ = dev RESERVED_ ->needed_ SPACE(dev) tailroom Our tunnel drivers try expanding headroom and the space for tunnel encapsulation was not a mandatory space -- so we are not seeing bugs here --, but just for optimization for performance critial situations. Since NDISC messages are not performance critical unlike TCP, and as we know outgoing device, LL_RESERVED_SPACE(dev) should be just enough for the device in most (if not all) cases: LL_RESERVED_SPACE(dev) <= LL_MAX_HEADER <= MAX_HEADER Note that LL_RESERVED_SPACE(dev) is also enough for NDISC over SIT (e.g., ISATAP). So, I think Option 1 is just fine here. Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org> --- net/ipv6/ndisc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)