linux协议栈(3.11)处理组播数据包流程
28 September 2013
ip_rcv -> ip_rcv_finish -> ip_route_input_noref -> ip_check_mc_rcu**
-> ip_route_input_mc -> fib_validate_source -> __fib_validate_source
-> dst->input -> ip_local_deliver/ip_mr_input
1816 int ip_route_input_noref(struct sk_buff *skb, __be32 daddr, __be32 saddr,
1817 u8 tos, struct net_device *dev)
1823 /* Multicast recognition logic is moved from route cache to here.
1824 The problem was that too many Ethernet cards have broken/missing
1825 hardware multicast filters :-( As result the host on multicasting
1826 network acquires a lot of useless route cache entries, sort of
1827 SDR messages from all the world. Now we try to get rid of them.
1828 Really, provided software IP multicast filter is organized
1829 reasonably (at least, hashed), it does not result in a slowdown
1830 comparing with route cache reject entries.
1831 Note, that multicast routers are not affected, because
1832 route cache entry is created eventually.
1833 */
1834 if (ipv4_is_multicast(daddr)) {
1835 struct in_device *in_dev = __in_dev_get_rcu(dev);
1836
1837 if (in_dev) {
// 送给本机的返回1（加入了相应组播组）
1838 int our = ip_check_mc_rcu(in_dev, daddr, saddr,
1839 ip_hdr(skb)->protocol);
1840 if (our
1841 #ifdef CONFIG_IP_MROUTE
1842 ||
1843 (!ipv4_is_local_multicast(daddr) &&
1844 IN_DEV_MFORWARD(in_dev)) // 判断是否送给本机或者配置了组播转发
1845 #endif
1846 ) {
1847 int res = ip_route_input_mc(skb, daddr, saddr,
1848 tos, dev, our);
1849 rcu_read_unlock();
1850 return res;
1851 }
1852 }
1853 rcu_read_unlock();
1854 return -EINVAL;
1855 }
2371 int ip_check_mc_rcu(struct in_device *in_dev, __be32 mc_addr, __be32 src_addr, u16 proto)
2378 mc_hash = rcu_dereference(in_dev->mc_hash);
2379 if (mc_hash) {
2380 u32 hash = hash_32((__force u32)mc_addr, MC_HASH_SZ_LOG);
2381
2382 for (im = rcu_dereference(mc_hash[hash]);
2383 im != NULL;
2384 im = rcu_dereference(im->next_hash)) {
2385 if (im->multiaddr == mc_addr) // 判断是否已经添加组播组
2386 break;
2387 }
2388 } else {
2389 for_each_pmc_rcu(in_dev, im) {
2390 if (im->multiaddr == mc_addr) // 判断是否已经添加组播组
2391 break;
2392 }
2393 }
2394 if (im && proto == IPPROTO_IGMP) {
2395 rv = 1; // igmp包
2396 } else if (im) { // 组播数据包
2397 if (src_addr) { // igmpv3增加的指定组播源控制功能（通过IP_ADD_SOURCE_MEMBERSHIP/IP_DROP_SOURCE_MEMBERSHIP配置）
2398 for (psf=im->sources; psf; psf=psf->sf_next) {
2399 if (psf->sf_inaddr == src_addr)
2400 break;
2401 }
2402 if (psf)
2403 rv = psf->sf_count[MCAST_INCLUDE] ||
2404 psf->sf_count[MCAST_EXCLUDE] !=
2405 im->sfcount[MCAST_EXCLUDE];
2406 else
2407 rv = im->sfcount[MCAST_EXCLUDE] != 0;
2408 } else
2409 rv = 1; /* unspecified source; tentatively allow */ // igmp v1/v2
2410 }
2411 return rv;
2412 }
1421 static int ip_route_input_mc(struct sk_buff *skb, __be32 daddr, __be32 saddr,
1422 u8 tos, struct net_device *dev, int our)
// 源地址为组播地址或者本地广播地址或协议非IP协议则返回
1434 if (ipv4_is_multicast(saddr) || ipv4_is_lbcast(saddr) ||
1435 skb->protocol != htons(ETH_P_IP))
1436 goto e_inval;
1437
1438 if (likely(!IN_DEV_ROUTE_LOCALNET(in_dev)))
1439 if (ipv4_is_loopback(saddr)) // 源地址为环回地址则返回
1440 goto e_inval;
1441
1442 if (ipv4_is_zeronet(saddr)) {
1443 if (!ipv4_is_local_multicast(daddr)) // 源地址全0且目标地址非本地组播地址（224.X.X.X）则返回
1444 goto e_inval;
1445 } else {
1446 err = fib_validate_source(skb, saddr, 0, tos, 0, dev,
1447 in_dev, &itag);
1448 if (err < 0)
1449 goto e_err;
1450 }
1451 rth = rt_dst_alloc(dev_net(dev)->loopback_dev,
1452 IN_DEV_CONF_GET(in_dev, NOPOLICY), false, false);
1453 if (!rth)
1454 goto e_nobufs;
1455
1456 #ifdef CONFIG_IP_ROUTE_CLASSID
1457 rth->dst.tclassid = itag;
1458 #endif
1459 rth->dst.output = ip_rt_bug;
1460
1461 rth->rt_genid = rt_genid(dev_net(dev));
1462 rth->rt_flags = RTCF_MULTICAST;
1463 rth->rt_type = RTN_MULTICAST;
1464 rth->rt_is_input= 1;
1465 rth->rt_iif = 0;
1466 rth->rt_pmtu = 0;
1467 rth->rt_gateway = 0;
1468 rth->rt_uses_gateway = 0;
1469 INIT_LIST_HEAD(&rth->rt_uncached);
1470 if (our) {
1471 rth->dst.input= ip_local_deliver; //
1472 rth->rt_flags |= RTCF_LOCAL;
1473 }
1474
1475 #ifdef CONFIG_IP_MROUTE
1476 if (!ipv4_is_local_multicast(daddr) && IN_DEV_MFORWARD(in_dev))
1477 rth->dst.input = ip_mr_input;
1478 #endif
234 /* Given (packet source, input interface) and optional (dst, oif, tos):
235 * - (main) check, that source is valid i.e. not broadcast or our local
236 * address.
237 * - figure out what "logical" interface this packet arrived
238 * and calculate "specific destination" address.
239 * - check, that packet arrived from expected physical interface.
240 * called with rcu_read_lock()
241 */
242 static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
243 u8 tos, int oif, struct net_device *dev,
244 int rpf, struct in_device *idev, u32 *itag)
252 fl4.flowi4_oif = 0;
253 fl4.flowi4_iif = oif;
254 fl4.daddr = src; // src反填入daddr
255 fl4.saddr = dst; // dst这里传入为0
256 fl4.flowi4_tos = tos;
257 fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
258
259 no_addr = idev->ifa_list == NULL;
260
261 accept_local = IN_DEV_ACCEPT_LOCAL(idev);
262 fl4.flowi4_mark = IN_DEV_SRC_VMARK(idev) ? skb->mark : 0;
263
264 net = dev_net(dev);
265 if (fib_lookup(net, &fl4, &res)) // 查路由表是否有dst（0）->src的相应表项
266 goto last_resort;
267 if (res.type != RTN_UNICAST) {
268 if (res.type != RTN_LOCAL || !accept_local)
269 goto e_inval;
270 }
271 fib_combine_itag(itag, &res);
272 dev_match = false;
273
274 #ifdef CONFIG_IP_ROUTE_MULTIPATH
275 for (ret = 0; ret < res.fi->fib_nhs; ret++) {
276 struct fib_nh *nh = &res.fi->fib_nh[ret];
277
278 if (nh->nh_dev == dev) { // 检查输入接口是否一致
279 dev_match = true;
280 break;
281 }
282 }
283 #else
284 if (FIB_RES_DEV(res) == dev) // 检查输入接口是否一致
285 dev_match = true;
286 #endif
287 if (dev_match) {
// 是否可直达，RT_SCOPE_HOST（发自链路直连的主机）和RS_SCOPE_NOWHERE（发自本机）可直达，否则不可直达（需经过网关）
288 ret = FIB_RES_NH(res).nh_scope >= RT_SCOPE_HOST;
289 return ret;
290 }
291 if (no_addr)
292 goto last_resort;
293 if (rpf == 1)
294 goto e_rpf;
295 fl4.flowi4_oif = dev->ifindex;
296
297 ret = 0;
298 if (fib_lookup(net, &fl4, &res) == 0) {
299 if (res.type == RTN_UNICAST)
300 ret = FIB_RES_NH(res).nh_scope >= RT_SCOPE_HOST;
301 }
302 return ret;
303
304 last_resort:
305 if (rpf)
306 goto e_rpf;
307 *itag = 0;
308 return 0;
309
310 e_inval:
311 return -EINVAL;
312 e_rpf:
313 return -EXDEV;
314 }
主机能接收组播包需满足的条件：
- 主机加入相应组播组
- 组播数据包源地址不能为组播地址、本地广播地址或环回地址
- 组播数据包源地址不能为全0同时目标地址为本地组播地址
- 主机配置了能和组播源连接的路由
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