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>

/*-----------------------------------------------------------------
 * Path-handling code, paths are held in lists
 *---------------------------------------------------------------*/
struct path_info {
	struct list_head list;
	struct 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 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 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(&pi->list, &s->valid_paths);

	return 0;
}

static void rr_fail_path(struct path_selector *ps, struct 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 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 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("round-robin: register failed %d", r);

	DMINFO("dm-round-robin 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("round-robin: 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");