Linux Kernel Networking: Implementation and Theory (Expert's Voice in Open Source)

By Rami Rosen

Linux Kernel Networking takes you on a guided in-depth travel of the present Linux networking implementation and the idea at the back of it. Linux kernel networking is a posh subject, so the e-book will not burden you with subject matters in some way concerning networking. This ebook also will no longer overload you with bulky line-by-line code walkthroughs in a roundabout way on the topic of what you are looking for; you will discover simply what you wish, with in-depth motives in each one bankruptcy and a short reference on the finish of every chapter.

Linux Kernel Networking is the single updated reference consultant to realizing how networking is carried out, and it'll be essential in future years on the grounds that such a lot of units now use Linux or working platforms in response to Linux, like Android, and because Linux is so familiar within the facts heart area, together with Linux-based virtualization applied sciences like Xen and KVM.

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Nexthop = (__force u32) rt_nexthop(rt, ip_hdr(skb)->daddr); neigh = __ipv4_neigh_lookup_noref(dev, nexthop); if (unlikely(! neigh)) neigh = __neigh_create(&arp_tbl, &nexthop, dev, false); if (! IS_ERR(neigh)) { int res = dst_neigh_output(dst, neigh, skb); . . . } Let’s have a look within the dst_neigh_output() procedure: static inline int dst_neigh_output(struct dst_entry *dst, struct neighbour *n, struct sk_buff *skb) { const struct hh_cache *hh; if (dst->pending_confirm) { unsigned lengthy now = jiffies; dst->pending_confirm = zero; /* steer clear of dirtying neighbour */ if (n->confirmed ! = now) n->confirmed = now; } if you achieve this technique for the 1st time with this circulate, nud_state isn't NUD_CONNECTED, and the output callback is the neigh_resolve_output() approach: hh = &n->hh; if ((n->nud_state & NUD_CONNECTED) && hh->hh_len) go back neigh_hh_output(hh, skb); else go back n->output(n, skb); } 177 CHAPTER 7 N LINUX NEIGHBOURING SUBSYSTEM (include/net/dst. h) within the neigh_resolve_output() procedure, you name the neigh_event_send() technique, which ultimately places the SKB within the arp_queue of the neighbour through __skb_queue_tail(&neigh->arp_queue, skb); later, the neigh_probe() procedure, invoked from the neighbour timer handler, neigh_timer_handler(), will ship the packet via invoking the solicit() strategy (neigh->ops->solicit is the arp_solicit() strategy in our case): static void neigh_probe(struct neighbour *neigh) __releases(neigh->lock) { struct sk_buff *skb = skb_peek(&neigh->arp_queue); . . . neigh->ops->solicit(neigh, skb); atomic_inc(&neigh->probes); kfree_skb(skb); } Let’s have a look at the arp_solicit() procedure, which truly sends the ARP request: static void arp_solicit(struct neighbour *neigh, struct sk_buff *skb) { __be32 saddr = zero; u8 dst_ha[MAX_ADDR_LEN], *dst_hw = NULL; struct net_device *dev = neigh->dev; __be32 objective = *(__be32 *)neigh->primary_key; int probes = atomic_read(&neigh->probes); struct in_device *in_dev; rcu_read_lock(); in_dev = __in_dev_get_rcu(dev); if (! in_dev) { rcu_read_unlock(); go back; } With the arp_announce procfs access, you could set regulations for which neighborhood resource IP deal with to exploit for the ARP packet you need to ship: u zero: Use any neighborhood handle, configured on any interface. this is often the default worth. u 1: First try and use addresses which are at the goal subnet. If there are not any such addresses, use point 2. u 2: Use fundamental IP handle. be aware that the max worth of those entries is used: /proc/sys/net/ipv4/conf/all/arp_announce /proc/sys/net/ipv4/conf//arp_announce 178 CHAPTER 7 N LINUX NEIGHBOURING SUBSYSTEM See additionally the outline of the IN_DEV_ARP_ANNOUNCE macro within the “Quick Reference” part on the finish of this bankruptcy. change (IN_DEV_ARP_ANNOUNCE(in_dev)) { default: case zero: /* by way of default announce any neighborhood IP */ if (skb && inet_addr_type(dev_net(dev), ip_hdr(skb)->saddr) == RTN_LOCAL) saddr = ip_hdr(skb)->saddr; holiday; case 1: /* limit bulletins of saddr in similar subnet */ if (! skb) holiday; saddr = ip_hdr(skb)->saddr; if (inet_addr_type(dev_net(dev), saddr) == RTN_LOCAL) { The inet_addr_onlink() technique exams even if the desired objective deal with and the desired resource tackle are at the related subnet: /* saddr may be identified to focus on */ if (inet_addr_onlink(in_dev, aim, saddr)) holiday; case 2: } saddr = zero; holiday; /* keep away from secondary IPs, get a primary/preferred one */ holiday; } rcu_read_unlock(); if (!

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