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