Call trace
forward a packet.
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| > ip_rcv_finish
> > ip_route_input_noref
> > > ip_route_input_slow
> > > > fib_lookup
> > > > ip_mkroute_input
> > dst_input(skb)
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| > > > > ip_mkroute_input
> > > > > __mkroute_input
> > > > > > rth = rt_dst_alloc(...)
> > > > > > skb_dst_set(skb, &rth->dst);
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| 1410 static struct rtable *rt_dst_alloc(struct net_device *dev,
1411 bool nopolicy, bool noxfrm, bool will_cache)
1412 {
1413 return dst_alloc(&ipv4_dst_ops, dev, 1, DST_OBSOLETE_FORCE_CHK,
1414 (will_cache ? 0 : (DST_HOST | DST_NOCACHE)) |
1415 (nopolicy ? DST_NOPOLICY : 0) |
1416 (noxfrm ? DST_NOXFRM : 0));
1417 }
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| 2711 int __init ip_rt_init(void)
2712 {
2713 int rc = 0;
2714
2715 #ifdef CONFIG_IP_ROUTE_CLASSID
2716 ip_rt_acct = __alloc_percpu(256 * sizeof(struct ip_rt_acct), __alignof__(struct ip_rt_acct));
2717 if (!ip_rt_acct)
2718 panic("IP: failed to allocate ip_rt_acct\n");
2719 #endif
2720
2721 ipv4_dst_ops.kmem_cachep =
2722 kmem_cache_create("ip_dst_cache", sizeof(struct rtable), 0,
2723 SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
2724
2725 ipv4_dst_blackhole_ops.kmem_cachep = ipv4_dst_ops.kmem_cachep;
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| 162 void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
163 int initial_ref, int initial_obsolete, unsigned short flags)
164 {
165 struct dst_entry *dst;
166
167 if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) {
168 if (ops->gc(ops))
169 return NULL;
170 }
171 dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
172 if (!dst)
173 return NULL;
174 dst->child = NULL;
175 dst->dev = dev;
176 if (dev)
177 dev_hold(dev);
178 dst->ops = ops;
179 dst_init_metrics(dst, dst_default_metrics, true);
180 dst->expires = 0UL;
181 dst->path = dst;
182 dst->from = NULL;
183 #ifdef CONFIG_XFRM
184 dst->xfrm = NULL;
185 #endif
186 dst->input = dst_discard;
187 dst->output = dst_discard;
188 dst->error = 0;
189 dst->obsolete = initial_obsolete;
190 dst->header_len = 0;
191 dst->trailer_len = 0;
192 #ifdef CONFIG_IP_ROUTE_CLASSID
193 dst->tclassid = 0;
194 #endif
195 atomic_set(&dst->__refcnt, initial_ref);
196 dst->__use = 0;
197 dst->lastuse = jiffies;
198 dst->flags = flags;
199 dst->pending_confirm = 0;
200 dst->next = NULL;
201 if (!(flags & DST_NOCOUNT))
202 dst_entries_add(ops, 1);
203 return dst;
204 }
205 EXPORT_SYMBOL(dst_alloc);
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| 1517
1518 static int __mkroute_input(struct sk_buff *skb,
1519 const struct fib_result *res,
1520 struct in_device *in_dev,
1521 __be32 daddr, __be32 saddr, u32 tos)
1522 {
...
1583 rth = rt_dst_alloc(out_dev->dev,
1584 IN_DEV_CONF_GET(in_dev, NOPOLICY),
1585 IN_DEV_CONF_GET(out_dev, NOXFRM), do_cache);
1586 if (!rth) {
1587 err = -ENOBUFS;
1588 goto cleanup;
1589 }
1590
1591 rth->rt_genid = rt_genid_ipv4(dev_net(rth->dst.dev));
1592 rth->rt_flags = flags;
1593 rth->rt_type = res->type;
1594 rth->rt_is_input = 1;
1595 rth->rt_iif = 0;
1596 rth->rt_pmtu = 0;
1597 rth->rt_gateway = 0;
1598 rth->rt_uses_gateway = 0;
1599 INIT_LIST_HEAD(&rth->rt_uncached);
1600
1601 rth->dst.input = ip_forward;
1602 rth->dst.output = ip_output;
1603
1604 rt_set_nexthop(rth, daddr, res, fnhe, res->fi, res->type, itag);
1605 skb_dst_set(skb, &rth->dst);
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dst functions
__refcnt is the important filed of struct dst_entry.
dst_hold
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| 235 static inline void dst_hold(struct dst_entry *dst)
236 {
237
241 BUILD_BUG_ON(offsetof(struct dst_entry, __refcnt) & 63);
242 atomic_inc(&dst->__refcnt);
243 }
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dst_clone
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| 258 static inline struct dst_entry *dst_clone(struct dst_entry *dst)
259 {
260 if (dst)
261 atomic_inc(&dst->__refcnt);
262 return dst;
263 }
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skb_dst_copy
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| 287 static inline void skb_dst_copy(struct sk_buff *nskb, const struct sk_buff *oskb)
288 {
289 nskb->_skb_refdst = oskb->_skb_refdst;
290 if (!(nskb->_skb_refdst & SKB_DST_NOREF))
291 dst_clone(skb_dst(nskb));
292 }
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dst free
If nobody is reference the dst, directly free it by dst_destroy,
else put it into the garbage collection list dst_garbage.list.
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| 370 static inline void dst_free(struct dst_entry *dst)
371 {
372 if (dst->obsolete > 0)
373 return;
374 if (!atomic_read(&dst->__refcnt)) {
375 dst = dst_destroy(dst);
376 if (!dst)
377 return;
378 }
379 __dst_free(dst);
380 }
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