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