Root/drivers/md/dm-round-robin.c

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

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