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