drivers/md/dm-path-selector.h

   1 /*
   2  * Copyright (C) 2003 Sistina Software.
   3  * Copyright (C) 2004 Red Hat, Inc. All rights reserved.
   4  *
   5  * Module Author: Heinz Mauelshagen
   6  *
   7  * This file is released under the GPL.
   8  *
   9  * Path-Selector registration.
  10  */
  11
  12 #ifndef DM_PATH_SELECTOR_H
  13 #define DM_PATH_SELECTOR_H
  14
  15 #include <linux/device-mapper.h>
  16
  17 #include "dm-mpath.h"
  18
  19 /*
  20  * We provide an abstraction for the code that chooses which path
  21  * to send some io down.
  22  */
  23 struct path_selector_type;
  24 struct path_selector {
  25         struct path_selector_type *type;
  26         void *context;
  27 };
  28
  29 /* Information about a path selector type */
  30 struct path_selector_type {
  31         char *name;
  32         struct module *module;
  33
  34         unsigned int table_args;
  35         unsigned int info_args;
  36
  37         /*
  38          * Constructs a path selector object, takes custom arguments
  39          */
  40         int (*create) (struct path_selector *ps, unsigned argc, char **argv);
  41         void (*destroy) (struct path_selector *ps);
  42
  43         /*
  44          * Add an opaque path object, along with some selector specific
  45          * path args (eg, path priority).
  46          */
  47         int (*add_path) (struct path_selector *ps, struct dm_path *path,
  48                          int argc, char **argv, char **error);
  49
  50         /*
  51          * Chooses a path for this io, if no paths are available then
  52          * NULL will be returned.
  53          *
  54          * repeat_count is the number of times to use the path before
  55          * calling the function again.  0 means don't call it again unless
  56          * the path fails.
  57          */
  58         struct dm_path *(*select_path) (struct path_selector *ps,
  59                                         unsigned *repeat_count,
  60                                         size_t nr_bytes);
  61
  62         /*
  63          * Notify the selector that a path has failed.
  64          */
  65         void (*fail_path) (struct path_selector *ps, struct dm_path *p);
  66
  67         /*
  68          * Ask selector to reinstate a path.
  69          */
  70         int (*reinstate_path) (struct path_selector *ps, struct dm_path *p);
  71
  72         /*
  73          * Table content based on parameters added in ps_add_path_fn
  74          * or path selector status
  75          */
  76         int (*status) (struct path_selector *ps, struct dm_path *path,
  77                        status_type_t type, char *result, unsigned int maxlen);
  78
  79         int (*start_io) (struct path_selector *ps, struct dm_path *path,
  80                          size_t nr_bytes);
  81         int (*end_io) (struct path_selector *ps, struct dm_path *path,
  82                        size_t nr_bytes);
  83 };
  84
  85 /* Register a path selector */
  86 int dm_register_path_selector(struct path_selector_type *type);
  87
  88 /* Unregister a path selector */
  89 int dm_unregister_path_selector(struct path_selector_type *type);
  90
  91 /* Returns a registered path selector type */
  92 struct path_selector_type *dm_get_path_selector(const char *name);
  93
  94 /* Releases a path selector  */
  95 void dm_put_path_selector(struct path_selector_type *pst);
  96
  97 #endif