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dm-round-robin.c

/*
 * Copyright (C) 2003 Sistina Software.
 * Copyright (C) 2004-2005 Red Hat, Inc. All rights reserved.
 *
 * Module Author: Heinz Mauelshagen
 *
 * This file is released under the GPL.
 *
 * Round-robin path selector.
 */

#include "dm.h"
#include "dm-path-selector.h"

#include <linux/slab.h>

#define DM_MSG_PREFIX "multipath round-robin"

/*-----------------------------------------------------------------
 * Path-handling code, paths are held in lists
 *---------------------------------------------------------------*/
struct path_info {
      struct list_head list;
      struct dm_path *path;
      unsigned repeat_count;
};

static void free_paths(struct list_head *paths)
{
      struct path_info *pi, *next;

      list_for_each_entry_safe(pi, next, paths, list) {
            list_del(&pi->list);
            kfree(pi);
      }
}

/*-----------------------------------------------------------------
 * Round-robin selector
 *---------------------------------------------------------------*/

#define RR_MIN_IO       1000

struct selector {
      struct list_head valid_paths;
      struct list_head invalid_paths;
};

static struct selector *alloc_selector(void)
{
      struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);

      if (s) {
            INIT_LIST_HEAD(&s->valid_paths);
            INIT_LIST_HEAD(&s->invalid_paths);
      }

      return s;
}

static int rr_create(struct path_selector *ps, unsigned argc, char **argv)
{
      struct selector *s;

      s = alloc_selector();
      if (!s)
            return -ENOMEM;

      ps->context = s;
      return 0;
}

static void rr_destroy(struct path_selector *ps)
{
      struct selector *s = (struct selector *) ps->context;

      free_paths(&s->valid_paths);
      free_paths(&s->invalid_paths);
      kfree(s);
      ps->context = NULL;
}

static int rr_status(struct path_selector *ps, struct dm_path *path,
                 status_type_t type, char *result, unsigned int maxlen)
{
      struct path_info *pi;
      int sz = 0;

      if (!path)
            DMEMIT("0 ");
      else {
            switch(type) {
            case STATUSTYPE_INFO:
                  break;
            case STATUSTYPE_TABLE:
                  pi = path->pscontext;
                  DMEMIT("%u ", pi->repeat_count);
                  break;
            }
      }

      return sz;
}

/*
 * Called during initialisation to register each path with an
 * optional repeat_count.
 */
static int rr_add_path(struct path_selector *ps, struct dm_path *path,
                   int argc, char **argv, char **error)
{
      struct selector *s = (struct selector *) ps->context;
      struct path_info *pi;
      unsigned repeat_count = RR_MIN_IO;

      if (argc > 1) {
            *error = "round-robin ps: incorrect number of arguments";
            return -EINVAL;
      }

      /* First path argument is number of I/Os before switching path */
      if ((argc == 1) && (sscanf(argv[0], "%u", &repeat_count) != 1)) {
            *error = "round-robin ps: invalid repeat count";
            return -EINVAL;
      }

      /* allocate the path */
      pi = kmalloc(sizeof(*pi), GFP_KERNEL);
      if (!pi) {
            *error = "round-robin ps: Error allocating path context";
            return -ENOMEM;
      }

      pi->path = path;
      pi->repeat_count = repeat_count;

      path->pscontext = pi;

      list_add_tail(&pi->list, &s->valid_paths);

      return 0;
}

static void rr_fail_path(struct path_selector *ps, struct dm_path *p)
{
      struct selector *s = (struct selector *) ps->context;
      struct path_info *pi = p->pscontext;

      list_move(&pi->list, &s->invalid_paths);
}

static int rr_reinstate_path(struct path_selector *ps, struct dm_path *p)
{
      struct selector *s = (struct selector *) ps->context;
      struct path_info *pi = p->pscontext;

      list_move(&pi->list, &s->valid_paths);

      return 0;
}

static struct dm_path *rr_select_path(struct path_selector *ps,
                           unsigned *repeat_count)
{
      struct selector *s = (struct selector *) ps->context;
      struct path_info *pi = NULL;

      if (!list_empty(&s->valid_paths)) {
            pi = list_entry(s->valid_paths.next, struct path_info, list);
            list_move_tail(&pi->list, &s->valid_paths);
            *repeat_count = pi->repeat_count;
      }

      return pi ? pi->path : NULL;
}

static struct path_selector_type rr_ps = {
      .name = "round-robin",
      .module = THIS_MODULE,
      .table_args = 1,
      .info_args = 0,
      .create = rr_create,
      .destroy = rr_destroy,
      .status = rr_status,
      .add_path = rr_add_path,
      .fail_path = rr_fail_path,
      .reinstate_path = rr_reinstate_path,
      .select_path = rr_select_path,
};

static int __init dm_rr_init(void)
{
      int r = dm_register_path_selector(&rr_ps);

      if (r < 0)
            DMERR("register failed %d", r);

      DMINFO("version 1.0.0 loaded");

      return r;
}

static void __exit dm_rr_exit(void)
{
      int r = dm_unregister_path_selector(&rr_ps);

      if (r < 0)
            DMERR("unregister failed %d", r);
}

module_init(dm_rr_init);
module_exit(dm_rr_exit);

MODULE_DESCRIPTION(DM_NAME " round-robin multipath path selector");
MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
MODULE_LICENSE("GPL");

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