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Linux/net/netfilter/ipvs/ip_vs_sh.c

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  1 // SPDX-License-Identifier: GPL-2.0-or-later
  2 /*
  3  * IPVS:        Source Hashing scheduling module
  4  *
  5  * Authors:     Wensong Zhang <wensong@gnuchina.org>
  6  *
  7  * Changes:
  8  */
  9 
 10 /*
 11  * The sh algorithm is to select server by the hash key of source IP
 12  * address. The pseudo code is as follows:
 13  *
 14  *       n <- servernode[src_ip];
 15  *       if (n is dead) OR
 16  *          (n is overloaded) or (n.weight <= 0) then
 17  *                 return NULL;
 18  *
 19  *       return n;
 20  *
 21  * Notes that servernode is a 256-bucket hash table that maps the hash
 22  * index derived from packet source IP address to the current server
 23  * array. If the sh scheduler is used in cache cluster, it is good to
 24  * combine it with cache_bypass feature. When the statically assigned
 25  * server is dead or overloaded, the load balancer can bypass the cache
 26  * server and send requests to the original server directly.
 27  *
 28  * The weight destination attribute can be used to control the
 29  * distribution of connections to the destinations in servernode. The
 30  * greater the weight, the more connections the destination
 31  * will receive.
 32  *
 33  */
 34 
 35 #define KMSG_COMPONENT "IPVS"
 36 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
 37 
 38 #include <linux/ip.h>
 39 #include <linux/slab.h>
 40 #include <linux/module.h>
 41 #include <linux/kernel.h>
 42 #include <linux/skbuff.h>
 43 
 44 #include <net/ip_vs.h>
 45 
 46 #include <net/tcp.h>
 47 #include <linux/udp.h>
 48 #include <linux/sctp.h>
 49 
 50 
 51 /*
 52  *      IPVS SH bucket
 53  */
 54 struct ip_vs_sh_bucket {
 55         struct ip_vs_dest __rcu *dest;  /* real server (cache) */
 56 };
 57 
 58 /*
 59  *     for IPVS SH entry hash table
 60  */
 61 #ifndef CONFIG_IP_VS_SH_TAB_BITS
 62 #define CONFIG_IP_VS_SH_TAB_BITS        8
 63 #endif
 64 #define IP_VS_SH_TAB_BITS               CONFIG_IP_VS_SH_TAB_BITS
 65 #define IP_VS_SH_TAB_SIZE               (1 << IP_VS_SH_TAB_BITS)
 66 #define IP_VS_SH_TAB_MASK               (IP_VS_SH_TAB_SIZE - 1)
 67 
 68 struct ip_vs_sh_state {
 69         struct rcu_head                 rcu_head;
 70         struct ip_vs_sh_bucket          buckets[IP_VS_SH_TAB_SIZE];
 71 };
 72 
 73 /* Helper function to determine if server is unavailable */
 74 static inline bool is_unavailable(struct ip_vs_dest *dest)
 75 {
 76         return atomic_read(&dest->weight) <= 0 ||
 77                dest->flags & IP_VS_DEST_F_OVERLOAD;
 78 }
 79 
 80 /*
 81  *      Returns hash value for IPVS SH entry
 82  */
 83 static inline unsigned int
 84 ip_vs_sh_hashkey(int af, const union nf_inet_addr *addr,
 85                  __be16 port, unsigned int offset)
 86 {
 87         __be32 addr_fold = addr->ip;
 88 
 89 #ifdef CONFIG_IP_VS_IPV6
 90         if (af == AF_INET6)
 91                 addr_fold = addr->ip6[0]^addr->ip6[1]^
 92                             addr->ip6[2]^addr->ip6[3];
 93 #endif
 94         return (offset + hash_32(ntohs(port) + ntohl(addr_fold),
 95                                  IP_VS_SH_TAB_BITS)) &
 96                 IP_VS_SH_TAB_MASK;
 97 }
 98 
 99 
100 /*
101  *      Get ip_vs_dest associated with supplied parameters.
102  */
103 static inline struct ip_vs_dest *
104 ip_vs_sh_get(struct ip_vs_service *svc, struct ip_vs_sh_state *s,
105              const union nf_inet_addr *addr, __be16 port)
106 {
107         unsigned int hash = ip_vs_sh_hashkey(svc->af, addr, port, 0);
108         struct ip_vs_dest *dest = rcu_dereference(s->buckets[hash].dest);
109 
110         return (!dest || is_unavailable(dest)) ? NULL : dest;
111 }
112 
113 
114 /* As ip_vs_sh_get, but with fallback if selected server is unavailable
115  *
116  * The fallback strategy loops around the table starting from a "random"
117  * point (in fact, it is chosen to be the original hash value to make the
118  * algorithm deterministic) to find a new server.
119  */
120 static inline struct ip_vs_dest *
121 ip_vs_sh_get_fallback(struct ip_vs_service *svc, struct ip_vs_sh_state *s,
122                       const union nf_inet_addr *addr, __be16 port)
123 {
124         unsigned int offset, roffset;
125         unsigned int hash, ihash;
126         struct ip_vs_dest *dest;
127 
128         /* first try the dest it's supposed to go to */
129         ihash = ip_vs_sh_hashkey(svc->af, addr, port, 0);
130         dest = rcu_dereference(s->buckets[ihash].dest);
131         if (!dest)
132                 return NULL;
133         if (!is_unavailable(dest))
134                 return dest;
135 
136         IP_VS_DBG_BUF(6, "SH: selected unavailable server %s:%d, reselecting",
137                       IP_VS_DBG_ADDR(dest->af, &dest->addr), ntohs(dest->port));
138 
139         /* if the original dest is unavailable, loop around the table
140          * starting from ihash to find a new dest
141          */
142         for (offset = 0; offset < IP_VS_SH_TAB_SIZE; offset++) {
143                 roffset = (offset + ihash) % IP_VS_SH_TAB_SIZE;
144                 hash = ip_vs_sh_hashkey(svc->af, addr, port, roffset);
145                 dest = rcu_dereference(s->buckets[hash].dest);
146                 if (!dest)
147                         break;
148                 if (!is_unavailable(dest))
149                         return dest;
150                 IP_VS_DBG_BUF(6, "SH: selected unavailable "
151                               "server %s:%d (offset %d), reselecting",
152                               IP_VS_DBG_ADDR(dest->af, &dest->addr),
153                               ntohs(dest->port), roffset);
154         }
155 
156         return NULL;
157 }
158 
159 /*
160  *      Assign all the hash buckets of the specified table with the service.
161  */
162 static int
163 ip_vs_sh_reassign(struct ip_vs_sh_state *s, struct ip_vs_service *svc)
164 {
165         int i;
166         struct ip_vs_sh_bucket *b;
167         struct list_head *p;
168         struct ip_vs_dest *dest;
169         int d_count;
170         bool empty;
171 
172         b = &s->buckets[0];
173         p = &svc->destinations;
174         empty = list_empty(p);
175         d_count = 0;
176         for (i=0; i<IP_VS_SH_TAB_SIZE; i++) {
177                 dest = rcu_dereference_protected(b->dest, 1);
178                 if (dest)
179                         ip_vs_dest_put(dest);
180                 if (empty)
181                         RCU_INIT_POINTER(b->dest, NULL);
182                 else {
183                         if (p == &svc->destinations)
184                                 p = p->next;
185 
186                         dest = list_entry(p, struct ip_vs_dest, n_list);
187                         ip_vs_dest_hold(dest);
188                         RCU_INIT_POINTER(b->dest, dest);
189 
190                         IP_VS_DBG_BUF(6, "assigned i: %d dest: %s weight: %d\n",
191                                       i, IP_VS_DBG_ADDR(dest->af, &dest->addr),
192                                       atomic_read(&dest->weight));
193 
194                         /* Don't move to next dest until filling weight */
195                         if (++d_count >= atomic_read(&dest->weight)) {
196                                 p = p->next;
197                                 d_count = 0;
198                         }
199 
200                 }
201                 b++;
202         }
203         return 0;
204 }
205 
206 
207 /*
208  *      Flush all the hash buckets of the specified table.
209  */
210 static void ip_vs_sh_flush(struct ip_vs_sh_state *s)
211 {
212         int i;
213         struct ip_vs_sh_bucket *b;
214         struct ip_vs_dest *dest;
215 
216         b = &s->buckets[0];
217         for (i=0; i<IP_VS_SH_TAB_SIZE; i++) {
218                 dest = rcu_dereference_protected(b->dest, 1);
219                 if (dest) {
220                         ip_vs_dest_put(dest);
221                         RCU_INIT_POINTER(b->dest, NULL);
222                 }
223                 b++;
224         }
225 }
226 
227 
228 static int ip_vs_sh_init_svc(struct ip_vs_service *svc)
229 {
230         struct ip_vs_sh_state *s;
231 
232         /* allocate the SH table for this service */
233         s = kzalloc(sizeof(struct ip_vs_sh_state), GFP_KERNEL);
234         if (s == NULL)
235                 return -ENOMEM;
236 
237         svc->sched_data = s;
238         IP_VS_DBG(6, "SH hash table (memory=%zdbytes) allocated for "
239                   "current service\n",
240                   sizeof(struct ip_vs_sh_bucket)*IP_VS_SH_TAB_SIZE);
241 
242         /* assign the hash buckets with current dests */
243         ip_vs_sh_reassign(s, svc);
244 
245         return 0;
246 }
247 
248 
249 static void ip_vs_sh_done_svc(struct ip_vs_service *svc)
250 {
251         struct ip_vs_sh_state *s = svc->sched_data;
252 
253         /* got to clean up hash buckets here */
254         ip_vs_sh_flush(s);
255 
256         /* release the table itself */
257         kfree_rcu(s, rcu_head);
258         IP_VS_DBG(6, "SH hash table (memory=%zdbytes) released\n",
259                   sizeof(struct ip_vs_sh_bucket)*IP_VS_SH_TAB_SIZE);
260 }
261 
262 
263 static int ip_vs_sh_dest_changed(struct ip_vs_service *svc,
264                                  struct ip_vs_dest *dest)
265 {
266         struct ip_vs_sh_state *s = svc->sched_data;
267 
268         /* assign the hash buckets with the updated service */
269         ip_vs_sh_reassign(s, svc);
270 
271         return 0;
272 }
273 
274 
275 /* Helper function to get port number */
276 static inline __be16
277 ip_vs_sh_get_port(const struct sk_buff *skb, struct ip_vs_iphdr *iph)
278 {
279         __be16 _ports[2], *ports;
280 
281         /* At this point we know that we have a valid packet of some kind.
282          * Because ICMP packets are only guaranteed to have the first 8
283          * bytes, let's just grab the ports.  Fortunately they're in the
284          * same position for all three of the protocols we care about.
285          */
286         switch (iph->protocol) {
287         case IPPROTO_TCP:
288         case IPPROTO_UDP:
289         case IPPROTO_SCTP:
290                 ports = skb_header_pointer(skb, iph->len, sizeof(_ports),
291                                            &_ports);
292                 if (unlikely(!ports))
293                         return 0;
294 
295                 if (likely(!ip_vs_iph_inverse(iph)))
296                         return ports[0];
297                 else
298                         return ports[1];
299         default:
300                 return 0;
301         }
302 }
303 
304 
305 /*
306  *      Source Hashing scheduling
307  */
308 static struct ip_vs_dest *
309 ip_vs_sh_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
310                   struct ip_vs_iphdr *iph)
311 {
312         struct ip_vs_dest *dest;
313         struct ip_vs_sh_state *s;
314         __be16 port = 0;
315         const union nf_inet_addr *hash_addr;
316 
317         hash_addr = ip_vs_iph_inverse(iph) ? &iph->daddr : &iph->saddr;
318 
319         IP_VS_DBG(6, "ip_vs_sh_schedule(): Scheduling...\n");
320 
321         if (svc->flags & IP_VS_SVC_F_SCHED_SH_PORT)
322                 port = ip_vs_sh_get_port(skb, iph);
323 
324         s = (struct ip_vs_sh_state *) svc->sched_data;
325 
326         if (svc->flags & IP_VS_SVC_F_SCHED_SH_FALLBACK)
327                 dest = ip_vs_sh_get_fallback(svc, s, hash_addr, port);
328         else
329                 dest = ip_vs_sh_get(svc, s, hash_addr, port);
330 
331         if (!dest) {
332                 ip_vs_scheduler_err(svc, "no destination available");
333                 return NULL;
334         }
335 
336         IP_VS_DBG_BUF(6, "SH: source IP address %s --> server %s:%d\n",
337                       IP_VS_DBG_ADDR(svc->af, hash_addr),
338                       IP_VS_DBG_ADDR(dest->af, &dest->addr),
339                       ntohs(dest->port));
340 
341         return dest;
342 }
343 
344 
345 /*
346  *      IPVS SH Scheduler structure
347  */
348 static struct ip_vs_scheduler ip_vs_sh_scheduler =
349 {
350         .name =                 "sh",
351         .refcnt =               ATOMIC_INIT(0),
352         .module =               THIS_MODULE,
353         .n_list  =              LIST_HEAD_INIT(ip_vs_sh_scheduler.n_list),
354         .init_service =         ip_vs_sh_init_svc,
355         .done_service =         ip_vs_sh_done_svc,
356         .add_dest =             ip_vs_sh_dest_changed,
357         .del_dest =             ip_vs_sh_dest_changed,
358         .upd_dest =             ip_vs_sh_dest_changed,
359         .schedule =             ip_vs_sh_schedule,
360 };
361 
362 
363 static int __init ip_vs_sh_init(void)
364 {
365         return register_ip_vs_scheduler(&ip_vs_sh_scheduler);
366 }
367 
368 
369 static void __exit ip_vs_sh_cleanup(void)
370 {
371         unregister_ip_vs_scheduler(&ip_vs_sh_scheduler);
372         synchronize_rcu();
373 }
374 
375 
376 module_init(ip_vs_sh_init);
377 module_exit(ip_vs_sh_cleanup);
378 MODULE_LICENSE("GPL");
379 

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