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		case STATUSTYPE_IMA:
105			*result = '\0';
106			break;
107		}
108	}
109
110	return sz;
111}
112
113/*
114 * Called during initialisation to register each path with an
115 * optional repeat_count.
116 */
117static int rr_add_path(struct path_selector *ps, struct dm_path *path,
118		       int argc, char **argv, char **error)
119{
120	struct selector *s = ps->context;
121	struct path_info *pi;
122	unsigned repeat_count = RR_MIN_IO;
123	char dummy;
124	unsigned long flags;
125
126	if (argc > 1) {
127		*error = "round-robin ps: incorrect number of arguments";
128		return -EINVAL;
129	}
130
131	/* First path argument is number of I/Os before switching path */
132	if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
133		*error = "round-robin ps: invalid repeat count";
134		return -EINVAL;
135	}
136
137	if (repeat_count > 1) {
138		DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
139		repeat_count = 1;
140	}
141
142	/* allocate the path */
143	pi = kmalloc(sizeof(*pi), GFP_KERNEL);
144	if (!pi) {
145		*error = "round-robin ps: Error allocating path context";
146		return -ENOMEM;
147	}
148
149	pi->path = path;
150	pi->repeat_count = repeat_count;
151
152	path->pscontext = pi;
153
154	spin_lock_irqsave(&s->lock, flags);
155	list_add_tail(&pi->list, &s->valid_paths);
156	spin_unlock_irqrestore(&s->lock, flags);
157
158	return 0;
159}
160
161static void rr_fail_path(struct path_selector *ps, struct dm_path *p)
162{
163	unsigned long flags;
164	struct selector *s = ps->context;
165	struct path_info *pi = p->pscontext;
166
167	spin_lock_irqsave(&s->lock, flags);
168	list_move(&pi->list, &s->invalid_paths);
169	spin_unlock_irqrestore(&s->lock, flags);
170}
171
172static int rr_reinstate_path(struct path_selector *ps, struct dm_path *p)
173{
174	unsigned long flags;
175	struct selector *s = ps->context;
176	struct path_info *pi = p->pscontext;
177
178	spin_lock_irqsave(&s->lock, flags);
179	list_move(&pi->list, &s->valid_paths);
180	spin_unlock_irqrestore(&s->lock, flags);
181
182	return 0;
183}
184
185static struct dm_path *rr_select_path(struct path_selector *ps, size_t nr_bytes)
186{
187	unsigned long flags;
188	struct selector *s = ps->context;
189	struct path_info *pi = NULL;
190
191	spin_lock_irqsave(&s->lock, flags);
192	if (!list_empty(&s->valid_paths)) {
193		pi = list_entry(s->valid_paths.next, struct path_info, list);
194		list_move_tail(&pi->list, &s->valid_paths);
195	}
196	spin_unlock_irqrestore(&s->lock, flags);
197
198	return pi ? pi->path : NULL;
199}
200
201static struct path_selector_type rr_ps = {
202	.name = "round-robin",
203	.module = THIS_MODULE,
204	.table_args = 1,
205	.info_args = 0,
206	.create = rr_create,
207	.destroy = rr_destroy,
208	.status = rr_status,
209	.add_path = rr_add_path,
210	.fail_path = rr_fail_path,
211	.reinstate_path = rr_reinstate_path,
212	.select_path = rr_select_path,
213};
214
215static int __init dm_rr_init(void)
216{
217	int r = dm_register_path_selector(&rr_ps);
218
219	if (r < 0)
220		DMERR("register failed %d", r);
221
222	DMINFO("version " RR_VERSION " loaded");
223
224	return r;
225}
226
227static void __exit dm_rr_exit(void)
228{
229	int r = dm_unregister_path_selector(&rr_ps);
230
231	if (r < 0)
232		DMERR("unregister failed %d", r);
233}
234
235module_init(dm_rr_init);
236module_exit(dm_rr_exit);
237
238MODULE_DESCRIPTION(DM_NAME " round-robin multipath path selector");
239MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
240MODULE_LICENSE("GPL");