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Linux/net/netfilter/ipvs/ip_vs_sh.c

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  1 /*
  2  * IPVS:        Source Hashing scheduling module
  3  *
  4  * Authors:     Wensong Zhang <wensong@gnuchina.org>
  5  *
  6  *              This program is free software; you can redistribute it and/or
  7  *              modify it under the terms of the GNU General Public License
  8  *              as published by the Free Software Foundation; either version
  9  *              2 of the License, or (at your option) any later version.
 10  *
 11  * Changes:
 12  *
 13  */
 14 
 15 /*
 16  * The sh algorithm is to select server by the hash key of source IP
 17  * address. The pseudo code is as follows:
 18  *
 19  *       n <- servernode[src_ip];
 20  *       if (n is dead) OR
 21  *          (n is overloaded) or (n.weight <= 0) then
 22  *                 return NULL;
 23  *
 24  *       return n;
 25  *
 26  * Notes that servernode is a 256-bucket hash table that maps the hash
 27  * index derived from packet source IP address to the current server
 28  * array. If the sh scheduler is used in cache cluster, it is good to
 29  * combine it with cache_bypass feature. When the statically assigned
 30  * server is dead or overloaded, the load balancer can bypass the cache
 31  * server and send requests to the original server directly.
 32  *
 33  * The weight destination attribute can be used to control the
 34  * distribution of connections to the destinations in servernode. The
 35  * greater the weight, the more connections the destination
 36  * will receive.
 37  *
 38  */
 39 
 40 #define KMSG_COMPONENT "IPVS"
 41 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
 42 
 43 #include <linux/ip.h>
 44 #include <linux/slab.h>
 45 #include <linux/module.h>
 46 #include <linux/kernel.h>
 47 #include <linux/skbuff.h>
 48 
 49 #include <net/ip_vs.h>
 50 
 51 #include <net/tcp.h>
 52 #include <linux/udp.h>
 53 #include <linux/sctp.h>
 54 
 55 
 56 /*
 57  *      IPVS SH bucket
 58  */
 59 struct ip_vs_sh_bucket {
 60         struct ip_vs_dest __rcu *dest;  /* real server (cache) */
 61 };
 62 
 63 /*
 64  *     for IPVS SH entry hash table
 65  */
 66 #ifndef CONFIG_IP_VS_SH_TAB_BITS
 67 #define CONFIG_IP_VS_SH_TAB_BITS        8
 68 #endif
 69 #define IP_VS_SH_TAB_BITS               CONFIG_IP_VS_SH_TAB_BITS
 70 #define IP_VS_SH_TAB_SIZE               (1 << IP_VS_SH_TAB_BITS)
 71 #define IP_VS_SH_TAB_MASK               (IP_VS_SH_TAB_SIZE - 1)
 72 
 73 struct ip_vs_sh_state {
 74         struct rcu_head                 rcu_head;
 75         struct ip_vs_sh_bucket          buckets[IP_VS_SH_TAB_SIZE];
 76 };
 77 
 78 /* Helper function to determine if server is unavailable */
 79 static inline bool is_unavailable(struct ip_vs_dest *dest)
 80 {
 81         return atomic_read(&dest->weight) <= 0 ||
 82                dest->flags & IP_VS_DEST_F_OVERLOAD;
 83 }
 84 
 85 /*
 86  *      Returns hash value for IPVS SH entry
 87  */
 88 static inline unsigned int
 89 ip_vs_sh_hashkey(int af, const union nf_inet_addr *addr,
 90                  __be16 port, unsigned int offset)
 91 {
 92         __be32 addr_fold = addr->ip;
 93 
 94 #ifdef CONFIG_IP_VS_IPV6
 95         if (af == AF_INET6)
 96                 addr_fold = addr->ip6[0]^addr->ip6[1]^
 97                             addr->ip6[2]^addr->ip6[3];
 98 #endif
 99         return (offset + (ntohs(port) + ntohl(addr_fold))*2654435761UL) &
100                 IP_VS_SH_TAB_MASK;
101 }
102 
103 
104 /*
105  *      Get ip_vs_dest associated with supplied parameters.
106  */
107 static inline struct ip_vs_dest *
108 ip_vs_sh_get(struct ip_vs_service *svc, struct ip_vs_sh_state *s,
109              const union nf_inet_addr *addr, __be16 port)
110 {
111         unsigned int hash = ip_vs_sh_hashkey(svc->af, addr, port, 0);
112         struct ip_vs_dest *dest = rcu_dereference(s->buckets[hash].dest);
113 
114         return (!dest || is_unavailable(dest)) ? NULL : dest;
115 }
116 
117 
118 /* As ip_vs_sh_get, but with fallback if selected server is unavailable
119  *
120  * The fallback strategy loops around the table starting from a "random"
121  * point (in fact, it is chosen to be the original hash value to make the
122  * algorithm deterministic) to find a new server.
123  */
124 static inline struct ip_vs_dest *
125 ip_vs_sh_get_fallback(struct ip_vs_service *svc, struct ip_vs_sh_state *s,
126                       const union nf_inet_addr *addr, __be16 port)
127 {
128         unsigned int offset, roffset;
129         unsigned int hash, ihash;
130         struct ip_vs_dest *dest;
131 
132         /* first try the dest it's supposed to go to */
133         ihash = ip_vs_sh_hashkey(svc->af, addr, port, 0);
134         dest = rcu_dereference(s->buckets[ihash].dest);
135         if (!dest)
136                 return NULL;
137         if (!is_unavailable(dest))
138                 return dest;
139 
140         IP_VS_DBG_BUF(6, "SH: selected unavailable server %s:%d, reselecting",
141                       IP_VS_DBG_ADDR(dest->af, &dest->addr), ntohs(dest->port));
142 
143         /* if the original dest is unavailable, loop around the table
144          * starting from ihash to find a new dest
145          */
146         for (offset = 0; offset < IP_VS_SH_TAB_SIZE; offset++) {
147                 roffset = (offset + ihash) % IP_VS_SH_TAB_SIZE;
148                 hash = ip_vs_sh_hashkey(svc->af, addr, port, roffset);
149                 dest = rcu_dereference(s->buckets[hash].dest);
150                 if (!dest)
151                         break;
152                 if (!is_unavailable(dest))
153                         return dest;
154                 IP_VS_DBG_BUF(6, "SH: selected unavailable "
155                               "server %s:%d (offset %d), reselecting",
156                               IP_VS_DBG_ADDR(dest->af, &dest->addr),
157                               ntohs(dest->port), roffset);
158         }
159 
160         return NULL;
161 }
162 
163 /*
164  *      Assign all the hash buckets of the specified table with the service.
165  */
166 static int
167 ip_vs_sh_reassign(struct ip_vs_sh_state *s, struct ip_vs_service *svc)
168 {
169         int i;
170         struct ip_vs_sh_bucket *b;
171         struct list_head *p;
172         struct ip_vs_dest *dest;
173         int d_count;
174         bool empty;
175 
176         b = &s->buckets[0];
177         p = &svc->destinations;
178         empty = list_empty(p);
179         d_count = 0;
180         for (i=0; i<IP_VS_SH_TAB_SIZE; i++) {
181                 dest = rcu_dereference_protected(b->dest, 1);
182                 if (dest)
183                         ip_vs_dest_put(dest);
184                 if (empty)
185                         RCU_INIT_POINTER(b->dest, NULL);
186                 else {
187                         if (p == &svc->destinations)
188                                 p = p->next;
189 
190                         dest = list_entry(p, struct ip_vs_dest, n_list);
191                         ip_vs_dest_hold(dest);
192                         RCU_INIT_POINTER(b->dest, dest);
193 
194                         IP_VS_DBG_BUF(6, "assigned i: %d dest: %s weight: %d\n",
195                                       i, IP_VS_DBG_ADDR(dest->af, &dest->addr),
196                                       atomic_read(&dest->weight));
197 
198                         /* Don't move to next dest until filling weight */
199                         if (++d_count >= atomic_read(&dest->weight)) {
200                                 p = p->next;
201                                 d_count = 0;
202                         }
203 
204                 }
205                 b++;
206         }
207         return 0;
208 }
209 
210 
211 /*
212  *      Flush all the hash buckets of the specified table.
213  */
214 static void ip_vs_sh_flush(struct ip_vs_sh_state *s)
215 {
216         int i;
217         struct ip_vs_sh_bucket *b;
218         struct ip_vs_dest *dest;
219 
220         b = &s->buckets[0];
221         for (i=0; i<IP_VS_SH_TAB_SIZE; i++) {
222                 dest = rcu_dereference_protected(b->dest, 1);
223                 if (dest) {
224                         ip_vs_dest_put(dest);
225                         RCU_INIT_POINTER(b->dest, NULL);
226                 }
227                 b++;
228         }
229 }
230 
231 
232 static int ip_vs_sh_init_svc(struct ip_vs_service *svc)
233 {
234         struct ip_vs_sh_state *s;
235 
236         /* allocate the SH table for this service */
237         s = kzalloc(sizeof(struct ip_vs_sh_state), GFP_KERNEL);
238         if (s == NULL)
239                 return -ENOMEM;
240 
241         svc->sched_data = s;
242         IP_VS_DBG(6, "SH hash table (memory=%zdbytes) allocated for "
243                   "current service\n",
244                   sizeof(struct ip_vs_sh_bucket)*IP_VS_SH_TAB_SIZE);
245 
246         /* assign the hash buckets with current dests */
247         ip_vs_sh_reassign(s, svc);
248 
249         return 0;
250 }
251 
252 
253 static void ip_vs_sh_done_svc(struct ip_vs_service *svc)
254 {
255         struct ip_vs_sh_state *s = svc->sched_data;
256 
257         /* got to clean up hash buckets here */
258         ip_vs_sh_flush(s);
259 
260         /* release the table itself */
261         kfree_rcu(s, rcu_head);
262         IP_VS_DBG(6, "SH hash table (memory=%zdbytes) released\n",
263                   sizeof(struct ip_vs_sh_bucket)*IP_VS_SH_TAB_SIZE);
264 }
265 
266 
267 static int ip_vs_sh_dest_changed(struct ip_vs_service *svc,
268                                  struct ip_vs_dest *dest)
269 {
270         struct ip_vs_sh_state *s = svc->sched_data;
271 
272         /* assign the hash buckets with the updated service */
273         ip_vs_sh_reassign(s, svc);
274 
275         return 0;
276 }
277 
278 
279 /* Helper function to get port number */
280 static inline __be16
281 ip_vs_sh_get_port(const struct sk_buff *skb, struct ip_vs_iphdr *iph)
282 {
283         __be16 _ports[2], *ports;
284 
285         /* At this point we know that we have a valid packet of some kind.
286          * Because ICMP packets are only guaranteed to have the first 8
287          * bytes, let's just grab the ports.  Fortunately they're in the
288          * same position for all three of the protocols we care about.
289          */
290         switch (iph->protocol) {
291         case IPPROTO_TCP:
292         case IPPROTO_UDP:
293         case IPPROTO_SCTP:
294                 ports = skb_header_pointer(skb, iph->len, sizeof(_ports),
295                                            &_ports);
296                 if (unlikely(!ports))
297                         return 0;
298 
299                 if (likely(!ip_vs_iph_inverse(iph)))
300                         return ports[0];
301                 else
302                         return ports[1];
303         default:
304                 return 0;
305         }
306 }
307 
308 
309 /*
310  *      Source Hashing scheduling
311  */
312 static struct ip_vs_dest *
313 ip_vs_sh_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
314                   struct ip_vs_iphdr *iph)
315 {
316         struct ip_vs_dest *dest;
317         struct ip_vs_sh_state *s;
318         __be16 port = 0;
319         const union nf_inet_addr *hash_addr;
320 
321         hash_addr = ip_vs_iph_inverse(iph) ? &iph->daddr : &iph->saddr;
322 
323         IP_VS_DBG(6, "ip_vs_sh_schedule(): Scheduling...\n");
324 
325         if (svc->flags & IP_VS_SVC_F_SCHED_SH_PORT)
326                 port = ip_vs_sh_get_port(skb, iph);
327 
328         s = (struct ip_vs_sh_state *) svc->sched_data;
329 
330         if (svc->flags & IP_VS_SVC_F_SCHED_SH_FALLBACK)
331                 dest = ip_vs_sh_get_fallback(svc, s, hash_addr, port);
332         else
333                 dest = ip_vs_sh_get(svc, s, hash_addr, port);
334 
335         if (!dest) {
336                 ip_vs_scheduler_err(svc, "no destination available");
337                 return NULL;
338         }
339 
340         IP_VS_DBG_BUF(6, "SH: source IP address %s --> server %s:%d\n",
341                       IP_VS_DBG_ADDR(svc->af, hash_addr),
342                       IP_VS_DBG_ADDR(dest->af, &dest->addr),
343                       ntohs(dest->port));
344 
345         return dest;
346 }
347 
348 
349 /*
350  *      IPVS SH Scheduler structure
351  */
352 static struct ip_vs_scheduler ip_vs_sh_scheduler =
353 {
354         .name =                 "sh",
355         .refcnt =               ATOMIC_INIT(0),
356         .module =               THIS_MODULE,
357         .n_list  =              LIST_HEAD_INIT(ip_vs_sh_scheduler.n_list),
358         .init_service =         ip_vs_sh_init_svc,
359         .done_service =         ip_vs_sh_done_svc,
360         .add_dest =             ip_vs_sh_dest_changed,
361         .del_dest =             ip_vs_sh_dest_changed,
362         .upd_dest =             ip_vs_sh_dest_changed,
363         .schedule =             ip_vs_sh_schedule,
364 };
365 
366 
367 static int __init ip_vs_sh_init(void)
368 {
369         return register_ip_vs_scheduler(&ip_vs_sh_scheduler);
370 }
371 
372 
373 static void __exit ip_vs_sh_cleanup(void)
374 {
375         unregister_ip_vs_scheduler(&ip_vs_sh_scheduler);
376         synchronize_rcu();
377 }
378 
379 
380 module_init(ip_vs_sh_init);
381 module_exit(ip_vs_sh_cleanup);
382 MODULE_LICENSE("GPL");
383 

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