/*
 * 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;

        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, 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 <dm-devel@redhat.com>");
MODULE_LICENSE("GPL");