Linux Cross Reference
Linux/drivers/md/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 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_tail(&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("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("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");