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#define RR_MIN_IO     1
21#define RR_VERSION    "1.2.0"
22
23/*-----------------------------------------------------------------
24 * Path-handling code, paths are held in lists
25 *---------------------------------------------------------------*/
26struct path_info {
27	struct list_head list;
28	struct dm_path *path;
29	unsigned repeat_count;
30};
31
32static void free_paths(struct list_head *paths)
33{
34	struct path_info *pi, *next;
35
36	list_for_each_entry_safe(pi, next, paths, list) {
37		list_del(&pi->list);
38		kfree(pi);
39	}
40}
41
42/*-----------------------------------------------------------------
43 * Round-robin selector
44 *---------------------------------------------------------------*/
45
46struct selector {
47	struct list_head valid_paths;
48	struct list_head invalid_paths;
49	spinlock_t lock;
50};
51
52static struct selector *alloc_selector(void)
53{
54	struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
55
56	if (s) {
57		INIT_LIST_HEAD(&s->valid_paths);
58		INIT_LIST_HEAD(&s->invalid_paths);
59		spin_lock_init(&s->lock);
60	}
61
62	return s;
63}
64
65static int rr_create(struct path_selector *ps, unsigned argc, char **argv)
66{
67	struct selector *s;
68
69	s = alloc_selector();
70	if (!s)
71		return -ENOMEM;
72
73	ps->context = s;
74	return 0;
75}
76
77static void rr_destroy(struct path_selector *ps)
78{
79	struct selector *s = ps->context;
80
81	free_paths(&s->valid_paths);
82	free_paths(&s->invalid_paths);
83	kfree(s);
84	ps->context = NULL;
85}
86
87static int rr_status(struct path_selector *ps, struct dm_path *path,
88		     status_type_t type, char *result, unsigned int maxlen)
89{
90	struct path_info *pi;
91	int sz = 0;
92
93	if (!path)
94		DMEMIT("0 ");
95	else {
96		switch(type) {
97		case STATUSTYPE_INFO:
98			break;
99		case STATUSTYPE_TABLE:
100			pi = path->pscontext;
101			DMEMIT("%u ", pi->repeat_count);
102			break;
103		}
104	}
105
106	return sz;
107}
108
109/*
110 * Called during initialisation to register each path with an
111 * optional repeat_count.
112 */
113static int rr_add_path(struct path_selector *ps, struct dm_path *path,
114		       int argc, char **argv, char **error)
115{
116	struct selector *s = ps->context;
117	struct path_info *pi;
118	unsigned repeat_count = RR_MIN_IO;
119	char dummy;
120	unsigned long flags;
121
122	if (argc > 1) {
123		*error = "round-robin ps: incorrect number of arguments";
124		return -EINVAL;
125	}
126
127	/* First path argument is number of I/Os before switching path */
128	if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
129		*error = "round-robin ps: invalid repeat count";
130		return -EINVAL;
131	}
132
133	if (repeat_count > 1) {
134		DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
135		repeat_count = 1;
136	}
137
138	/* allocate the path */
139	pi = kmalloc(sizeof(*pi), GFP_KERNEL);
140	if (!pi) {
141		*error = "round-robin ps: Error allocating path context";
142		return -ENOMEM;
143	}
144
145	pi->path = path;
146	pi->repeat_count = repeat_count;
147
148	path->pscontext = pi;
149
150	spin_lock_irqsave(&s->lock, flags);
151	list_add_tail(&pi->list, &s->valid_paths);
152	spin_unlock_irqrestore(&s->lock, flags);
153
154	return 0;
155}
156
157static void rr_fail_path(struct path_selector *ps, struct dm_path *p)
158{
159	unsigned long flags;
160	struct selector *s = ps->context;
161	struct path_info *pi = p->pscontext;
162
163	spin_lock_irqsave(&s->lock, flags);
164	list_move(&pi->list, &s->invalid_paths);
165	spin_unlock_irqrestore(&s->lock, flags);
166}
167
168static int rr_reinstate_path(struct path_selector *ps, struct dm_path *p)
169{
170	unsigned long flags;
171	struct selector *s = ps->context;
172	struct path_info *pi = p->pscontext;
173
174	spin_lock_irqsave(&s->lock, flags);
175	list_move(&pi->list, &s->valid_paths);
176	spin_unlock_irqrestore(&s->lock, flags);
177
178	return 0;
179}
180
181static struct dm_path *rr_select_path(struct path_selector *ps, size_t nr_bytes)
182{
183	unsigned long flags;
184	struct selector *s = ps->context;
185	struct path_info *pi = NULL;
186
187	spin_lock_irqsave(&s->lock, flags);
188	if (!list_empty(&s->valid_paths)) {
189		pi = list_entry(s->valid_paths.next, struct path_info, list);
190		list_move_tail(&pi->list, &s->valid_paths);
191	}
192	spin_unlock_irqrestore(&s->lock, flags);
193
194	return pi ? pi->path : NULL;
195}
196
197static struct path_selector_type rr_ps = {
198	.name = "round-robin",
199	.module = THIS_MODULE,
200	.table_args = 1,
201	.info_args = 0,
202	.create = rr_create,
203	.destroy = rr_destroy,
204	.status = rr_status,
205	.add_path = rr_add_path,
206	.fail_path = rr_fail_path,
207	.reinstate_path = rr_reinstate_path,
208	.select_path = rr_select_path,
209};
210
211static int __init dm_rr_init(void)
212{
213	int r = dm_register_path_selector(&rr_ps);
214
215	if (r < 0)
216		DMERR("register failed %d", r);
217
218	DMINFO("version " RR_VERSION " loaded");
219
220	return r;
221}
222
223static void __exit dm_rr_exit(void)
224{
225	int r = dm_unregister_path_selector(&rr_ps);
226
227	if (r < 0)
228		DMERR("unregister failed %d", r);
229}
230
231module_init(dm_rr_init);
232module_exit(dm_rr_exit);
233
234MODULE_DESCRIPTION(DM_NAME " round-robin multipath path selector");
235MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
236MODULE_LICENSE("GPL");
237