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 <linux/device-mapper.h>
13
14#include "dm-path-selector.h"
15
16#include <linux/slab.h>
17#include <linux/module.h>
18
19#define DM_MSG_PREFIX "multipath round-robin"
20
21/*-----------------------------------------------------------------
22 * Path-handling code, paths are held in lists
23 *---------------------------------------------------------------*/
24struct path_info {
25	struct list_head list;
26	struct dm_path *path;
27	unsigned repeat_count;
28};
29
30static void free_paths(struct list_head *paths)
31{
32	struct path_info *pi, *next;
33
34	list_for_each_entry_safe(pi, next, paths, list) {
35		list_del(&pi->list);
36		kfree(pi);
37	}
38}
39
40/*-----------------------------------------------------------------
41 * Round-robin selector
42 *---------------------------------------------------------------*/
43
44#define RR_MIN_IO		1000
45
46struct selector {
47	struct list_head valid_paths;
48	struct list_head invalid_paths;
49};
50
51static struct selector *alloc_selector(void)
52{
53	struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
54
55	if (s) {
56		INIT_LIST_HEAD(&s->valid_paths);
57		INIT_LIST_HEAD(&s->invalid_paths);
58	}
59
60	return s;
61}
62
63static int rr_create(struct path_selector *ps, unsigned argc, char **argv)
64{
65	struct selector *s;
66
67	s = alloc_selector();
68	if (!s)
69		return -ENOMEM;
70
71	ps->context = s;
72	return 0;
73}
74
75static void rr_destroy(struct path_selector *ps)
76{
77	struct selector *s = (struct selector *) ps->context;
78
79	free_paths(&s->valid_paths);
80	free_paths(&s->invalid_paths);
81	kfree(s);
82	ps->context = NULL;
83}
84
85static int rr_status(struct path_selector *ps, struct dm_path *path,
86		     status_type_t type, char *result, unsigned int maxlen)
87{
88	struct path_info *pi;
89	int sz = 0;
90
91	if (!path)
92		DMEMIT("0 ");
93	else {
94		switch(type) {
95		case STATUSTYPE_INFO:
96			break;
97		case STATUSTYPE_TABLE:
98			pi = path->pscontext;
99			DMEMIT("%u ", pi->repeat_count);
100			break;
101		}
102	}
103
104	return sz;
105}
106
107/*
108 * Called during initialisation to register each path with an
109 * optional repeat_count.
110 */
111static int rr_add_path(struct path_selector *ps, struct dm_path *path,
112		       int argc, char **argv, char **error)
113{
114	struct selector *s = (struct selector *) ps->context;
115	struct path_info *pi;
116	unsigned repeat_count = RR_MIN_IO;
117	char dummy;
118
119	if (argc > 1) {
120		*error = "round-robin ps: incorrect number of arguments";
121		return -EINVAL;
122	}
123
124	/* First path argument is number of I/Os before switching path */
125	if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
126		*error = "round-robin ps: invalid repeat count";
127		return -EINVAL;
128	}
129
130	/* allocate the path */
131	pi = kmalloc(sizeof(*pi), GFP_KERNEL);
132	if (!pi) {
133		*error = "round-robin ps: Error allocating path context";
134		return -ENOMEM;
135	}
136
137	pi->path = path;
138	pi->repeat_count = repeat_count;
139
140	path->pscontext = pi;
141
142	list_add_tail(&pi->list, &s->valid_paths);
143
144	return 0;
145}
146
147static void rr_fail_path(struct path_selector *ps, struct dm_path *p)
148{
149	struct selector *s = (struct selector *) ps->context;
150	struct path_info *pi = p->pscontext;
151
152	list_move(&pi->list, &s->invalid_paths);
153}
154
155static int rr_reinstate_path(struct path_selector *ps, struct dm_path *p)
156{
157	struct selector *s = (struct selector *) ps->context;
158	struct path_info *pi = p->pscontext;
159
160	list_move(&pi->list, &s->valid_paths);
161
162	return 0;
163}
164
165static struct dm_path *rr_select_path(struct path_selector *ps,
166				      unsigned *repeat_count, size_t nr_bytes)
167{
168	struct selector *s = (struct selector *) ps->context;
169	struct path_info *pi = NULL;
170
171	if (!list_empty(&s->valid_paths)) {
172		pi = list_entry(s->valid_paths.next, struct path_info, list);
173		list_move_tail(&pi->list, &s->valid_paths);
174		*repeat_count = pi->repeat_count;
175	}
176
177	return pi ? pi->path : NULL;
178}
179
180static struct path_selector_type rr_ps = {
181	.name = "round-robin",
182	.module = THIS_MODULE,
183	.table_args = 1,
184	.info_args = 0,
185	.create = rr_create,
186	.destroy = rr_destroy,
187	.status = rr_status,
188	.add_path = rr_add_path,
189	.fail_path = rr_fail_path,
190	.reinstate_path = rr_reinstate_path,
191	.select_path = rr_select_path,
192};
193
194static int __init dm_rr_init(void)
195{
196	int r = dm_register_path_selector(&rr_ps);
197
198	if (r < 0)
199		DMERR("register failed %d", r);
200
201	DMINFO("version 1.0.0 loaded");
202
203	return r;
204}
205
206static void __exit dm_rr_exit(void)
207{
208	int r = dm_unregister_path_selector(&rr_ps);
209
210	if (r < 0)
211		DMERR("unregister failed %d", r);
212}
213
214module_init(dm_rr_init);
215module_exit(dm_rr_exit);
216
217MODULE_DESCRIPTION(DM_NAME " round-robin multipath path selector");
218MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
219MODULE_LICENSE("GPL");
220