1/*
2 * Copyright (C) 2003 Sistina Software.
3 * Copyright (C) 2004-2005 Red Hat, Inc. All rights reserved.
4 *
5 * Module Author: Heinz Mauelshagen
6 *
7 * This file is released under the GPL.
8 *
9 * Round-robin path selector.
10 */
11
12#include "dm.h"
13#include "dm-path-selector.h"
14
15#include <linux/slab.h>
16
17#define DM_MSG_PREFIX "multipath round-robin"
18
19/*-----------------------------------------------------------------
20 * Path-handling code, paths are held in lists
21 *---------------------------------------------------------------*/
22struct path_info {
23	struct list_head list;
24	struct dm_path *path;
25	unsigned repeat_count;
26};
27
28static void free_paths(struct list_head *paths)
29{
30	struct path_info *pi, *next;
31
32	list_for_each_entry_safe(pi, next, paths, list) {
33		list_del(&pi->list);
34		kfree(pi);
35	}
36}
37
38/*-----------------------------------------------------------------
39 * Round-robin selector
40 *---------------------------------------------------------------*/
41
42#define RR_MIN_IO		1000
43
44struct selector {
45	struct list_head valid_paths;
46	struct list_head invalid_paths;
47};
48
49static struct selector *alloc_selector(void)
50{
51	struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
52
53	if (s) {
54		INIT_LIST_HEAD(&s->valid_paths);
55		INIT_LIST_HEAD(&s->invalid_paths);
56	}
57
58	return s;
59}
60
61static int rr_create(struct path_selector *ps, unsigned argc, char **argv)
62{
63	struct selector *s;
64
65	s = alloc_selector();
66	if (!s)
67		return -ENOMEM;
68
69	ps->context = s;
70	return 0;
71}
72
73static void rr_destroy(struct path_selector *ps)
74{
75	struct selector *s = (struct selector *) ps->context;
76
77	free_paths(&s->valid_paths);
78	free_paths(&s->invalid_paths);
79	kfree(s);
80	ps->context = NULL;
81}
82
83static int rr_status(struct path_selector *ps, struct dm_path *path,
84		     status_type_t type, char *result, unsigned int maxlen)
85{
86	struct path_info *pi;
87	int sz = 0;
88
89	if (!path)
90		DMEMIT("0 ");
91	else {
92		switch(type) {
93		case STATUSTYPE_INFO:
94			break;
95		case STATUSTYPE_TABLE:
96			pi = path->pscontext;
97			DMEMIT("%u ", pi->repeat_count);
98			break;
99		}
100	}
101
102	return sz;
103}
104
105/*
106 * Called during initialisation to register each path with an
107 * optional repeat_count.
108 */
109static int rr_add_path(struct path_selector *ps, struct dm_path *path,
110		       int argc, char **argv, char **error)
111{
112	struct selector *s = (struct selector *) ps->context;
113	struct path_info *pi;
114	unsigned repeat_count = RR_MIN_IO;
115
116	if (argc > 1) {
117		*error = "round-robin ps: incorrect number of arguments";
118		return -EINVAL;
119	}
120
121	/* First path argument is number of I/Os before switching path */
122	if ((argc == 1) && (sscanf(argv[0], "%u", &repeat_count) != 1)) {
123		*error = "round-robin ps: invalid repeat count";
124		return -EINVAL;
125	}
126
127	/* allocate the path */
128	pi = kmalloc(sizeof(*pi), GFP_KERNEL);
129	if (!pi) {
130		*error = "round-robin ps: Error allocating path context";
131		return -ENOMEM;
132	}
133
134	pi->path = path;
135	pi->repeat_count = repeat_count;
136
137	path->pscontext = pi;
138
139	list_add_tail(&pi->list, &s->valid_paths);
140
141	return 0;
142}
143
144static void rr_fail_path(struct path_selector *ps, struct dm_path *p)
145{
146	struct selector *s = (struct selector *) ps->context;
147	struct path_info *pi = p->pscontext;
148
149	list_move(&pi->list, &s->invalid_paths);
150}
151
152static int rr_reinstate_path(struct path_selector *ps, struct dm_path *p)
153{
154	struct selector *s = (struct selector *) ps->context;
155	struct path_info *pi = p->pscontext;
156
157	list_move(&pi->list, &s->valid_paths);
158
159	return 0;
160}
161
162static struct dm_path *rr_select_path(struct path_selector *ps,
163				   unsigned *repeat_count)
164{
165	struct selector *s = (struct selector *) ps->context;
166	struct path_info *pi = NULL;
167
168	if (!list_empty(&s->valid_paths)) {
169		pi = list_entry(s->valid_paths.next, struct path_info, list);
170		list_move_tail(&pi->list, &s->valid_paths);
171		*repeat_count = pi->repeat_count;
172	}
173
174	return pi ? pi->path : NULL;
175}
176
177static struct path_selector_type rr_ps = {
178	.name = "round-robin",
179	.module = THIS_MODULE,
180	.table_args = 1,
181	.info_args = 0,
182	.create = rr_create,
183	.destroy = rr_destroy,
184	.status = rr_status,
185	.add_path = rr_add_path,
186	.fail_path = rr_fail_path,
187	.reinstate_path = rr_reinstate_path,
188	.select_path = rr_select_path,
189};
190
191static int __init dm_rr_init(void)
192{
193	int r = dm_register_path_selector(&rr_ps);
194
195	if (r < 0)
196		DMERR("register failed %d", r);
197
198	DMINFO("version 1.0.0 loaded");
199
200	return r;
201}
202
203static void __exit dm_rr_exit(void)
204{
205	int r = dm_unregister_path_selector(&rr_ps);
206
207	if (r < 0)
208		DMERR("round-robin: unregister failed %d", r);
209}
210
211module_init(dm_rr_init);
212module_exit(dm_rr_exit);
213
214MODULE_DESCRIPTION(DM_NAME " round-robin multipath path selector");
215MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
216MODULE_LICENSE("GPL");
217