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");