dm-round-robin.c

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/*
 * 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 <linux/device-mapper.h>

#include "dm-path-selector.h"

#include <linux/slab.h>
#include <linux/module.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;
    char dummy;

    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%c", &repeat_count, &dummy) != 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, size_t nr_bytes)
{
    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 <[email protected]>");
MODULE_LICENSE("GPL");