1/*
2 * IPVS:        Destination Hashing scheduling module
3 *
4 * Version:     $Id: ip_vs_dh.c,v 1.1.1.1 2007/08/03 18:53:51 Exp $
5 *
6 * Authors:     Wensong Zhang <wensong@gnuchina.org>
7 *
8 *              Inspired by the consistent hashing scheduler patch from
9 *              Thomas Proell <proellt@gmx.de>
10 *
11 *              This program is free software; you can redistribute it and/or
12 *              modify it under the terms of the GNU General Public License
13 *              as published by the Free Software Foundation; either version
14 *              2 of the License, or (at your option) any later version.
15 *
16 * Changes:
17 *
18 */
19
20/*
21 * The dh algorithm is to select server by the hash key of destination IP
22 * address. The pseudo code is as follows:
23 *
24 *       n <- servernode[dest_ip];
25 *       if (n is dead) OR
26 *          (n is overloaded) OR (n.weight <= 0) then
27 *                 return NULL;
28 *
29 *       return n;
30 *
31 * Notes that servernode is a 256-bucket hash table that maps the hash
32 * index derived from packet destination IP address to the current server
33 * array. If the dh scheduler is used in cache cluster, it is good to
34 * combine it with cache_bypass feature. When the statically assigned
35 * server is dead or overloaded, the load balancer can bypass the cache
36 * server and send requests to the original server directly.
37 *
38 */
39
40#include <linux/ip.h>
41#include <linux/module.h>
42#include <linux/kernel.h>
43#include <linux/skbuff.h>
44
45#include <net/ip_vs.h>
46
47
48/*
49 *      IPVS DH bucket
50 */
51struct ip_vs_dh_bucket {
52	struct ip_vs_dest       *dest;          /* real server (cache) */
53};
54
55/*
56 *     for IPVS DH entry hash table
57 */
58#ifndef CONFIG_IP_VS_DH_TAB_BITS
59#define CONFIG_IP_VS_DH_TAB_BITS        8
60#endif
61#define IP_VS_DH_TAB_BITS               CONFIG_IP_VS_DH_TAB_BITS
62#define IP_VS_DH_TAB_SIZE               (1 << IP_VS_DH_TAB_BITS)
63#define IP_VS_DH_TAB_MASK               (IP_VS_DH_TAB_SIZE - 1)
64
65
66/*
67 *	Returns hash value for IPVS DH entry
68 */
69static inline unsigned ip_vs_dh_hashkey(__be32 addr)
70{
71	return (ntohl(addr)*2654435761UL) & IP_VS_DH_TAB_MASK;
72}
73
74
75/*
76 *      Get ip_vs_dest associated with supplied parameters.
77 */
78static inline struct ip_vs_dest *
79ip_vs_dh_get(struct ip_vs_dh_bucket *tbl, __be32 addr)
80{
81	return (tbl[ip_vs_dh_hashkey(addr)]).dest;
82}
83
84
85/*
86 *      Assign all the hash buckets of the specified table with the service.
87 */
88static int
89ip_vs_dh_assign(struct ip_vs_dh_bucket *tbl, struct ip_vs_service *svc)
90{
91	int i;
92	struct ip_vs_dh_bucket *b;
93	struct list_head *p;
94	struct ip_vs_dest *dest;
95
96	b = tbl;
97	p = &svc->destinations;
98	for (i=0; i<IP_VS_DH_TAB_SIZE; i++) {
99		if (list_empty(p)) {
100			b->dest = NULL;
101		} else {
102			if (p == &svc->destinations)
103				p = p->next;
104
105			dest = list_entry(p, struct ip_vs_dest, n_list);
106			atomic_inc(&dest->refcnt);
107			b->dest = dest;
108
109			p = p->next;
110		}
111		b++;
112	}
113	return 0;
114}
115
116
117/*
118 *      Flush all the hash buckets of the specified table.
119 */
120static void ip_vs_dh_flush(struct ip_vs_dh_bucket *tbl)
121{
122	int i;
123	struct ip_vs_dh_bucket *b;
124
125	b = tbl;
126	for (i=0; i<IP_VS_DH_TAB_SIZE; i++) {
127		if (b->dest) {
128			atomic_dec(&b->dest->refcnt);
129			b->dest = NULL;
130		}
131		b++;
132	}
133}
134
135
136static int ip_vs_dh_init_svc(struct ip_vs_service *svc)
137{
138	struct ip_vs_dh_bucket *tbl;
139
140	/* allocate the DH table for this service */
141	tbl = kmalloc(sizeof(struct ip_vs_dh_bucket)*IP_VS_DH_TAB_SIZE,
142		      GFP_ATOMIC);
143	if (tbl == NULL) {
144		IP_VS_ERR("ip_vs_dh_init_svc(): no memory\n");
145		return -ENOMEM;
146	}
147	svc->sched_data = tbl;
148	IP_VS_DBG(6, "DH hash table (memory=%Zdbytes) allocated for "
149		  "current service\n",
150		  sizeof(struct ip_vs_dh_bucket)*IP_VS_DH_TAB_SIZE);
151
152	/* assign the hash buckets with the updated service */
153	ip_vs_dh_assign(tbl, svc);
154
155	return 0;
156}
157
158
159static int ip_vs_dh_done_svc(struct ip_vs_service *svc)
160{
161	struct ip_vs_dh_bucket *tbl = svc->sched_data;
162
163	/* got to clean up hash buckets here */
164	ip_vs_dh_flush(tbl);
165
166	/* release the table itself */
167	kfree(svc->sched_data);
168	IP_VS_DBG(6, "DH hash table (memory=%Zdbytes) released\n",
169		  sizeof(struct ip_vs_dh_bucket)*IP_VS_DH_TAB_SIZE);
170
171	return 0;
172}
173
174
175static int ip_vs_dh_update_svc(struct ip_vs_service *svc)
176{
177	struct ip_vs_dh_bucket *tbl = svc->sched_data;
178
179	/* got to clean up hash buckets here */
180	ip_vs_dh_flush(tbl);
181
182	/* assign the hash buckets with the updated service */
183	ip_vs_dh_assign(tbl, svc);
184
185	return 0;
186}
187
188
189/*
190 *      If the dest flags is set with IP_VS_DEST_F_OVERLOAD,
191 *      consider that the server is overloaded here.
192 */
193static inline int is_overloaded(struct ip_vs_dest *dest)
194{
195	return dest->flags & IP_VS_DEST_F_OVERLOAD;
196}
197
198
199/*
200 *      Destination hashing scheduling
201 */
202static struct ip_vs_dest *
203ip_vs_dh_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
204{
205	struct ip_vs_dest *dest;
206	struct ip_vs_dh_bucket *tbl;
207	struct iphdr *iph = ip_hdr(skb);
208
209	IP_VS_DBG(6, "ip_vs_dh_schedule(): Scheduling...\n");
210
211	tbl = (struct ip_vs_dh_bucket *)svc->sched_data;
212	dest = ip_vs_dh_get(tbl, iph->daddr);
213	if (!dest
214	    || !(dest->flags & IP_VS_DEST_F_AVAILABLE)
215	    || atomic_read(&dest->weight) <= 0
216	    || is_overloaded(dest)) {
217		return NULL;
218	}
219
220	IP_VS_DBG(6, "DH: destination IP address %u.%u.%u.%u "
221		  "--> server %u.%u.%u.%u:%d\n",
222		  NIPQUAD(iph->daddr),
223		  NIPQUAD(dest->addr),
224		  ntohs(dest->port));
225
226	return dest;
227}
228
229
230/*
231 *      IPVS DH Scheduler structure
232 */
233static struct ip_vs_scheduler ip_vs_dh_scheduler =
234{
235	.name =			"dh",
236	.refcnt =		ATOMIC_INIT(0),
237	.module =		THIS_MODULE,
238	.init_service =		ip_vs_dh_init_svc,
239	.done_service =		ip_vs_dh_done_svc,
240	.update_service =	ip_vs_dh_update_svc,
241	.schedule =		ip_vs_dh_schedule,
242};
243
244
245static int __init ip_vs_dh_init(void)
246{
247	INIT_LIST_HEAD(&ip_vs_dh_scheduler.n_list);
248	return register_ip_vs_scheduler(&ip_vs_dh_scheduler);
249}
250
251
252static void __exit ip_vs_dh_cleanup(void)
253{
254	unregister_ip_vs_scheduler(&ip_vs_dh_scheduler);
255}
256
257
258module_init(ip_vs_dh_init);
259module_exit(ip_vs_dh_cleanup);
260MODULE_LICENSE("GPL");
261