drivers/md/dm-target.c

   1 /*
   2  * Copyright (C) 2001 Sistina Software (UK) Limited
   3  *
   4  * This file is released under the GPL.
   5  */
   6
   7 #include "dm.h"
   8
   9 #include <linux/module.h>
  10 #include <linux/init.h>
  11 #include <linux/kmod.h>
  12 #include <linux/bio.h>
  13
  14 #define DM_MSG_PREFIX "target"
  15
  16 static LIST_HEAD(_targets);
  17 static DECLARE_RWSEM(_lock);
  18
  19 #define DM_MOD_NAME_SIZE 32
  20
  21 static inline struct target_type *__find_target_type(const char *name)
  22 {
  23         struct target_type *tt;
  24
  25         list_for_each_entry(tt, &_targets, list)
  26                 if (!strcmp(name, tt->name))
  27                         return tt;
  28
  29         return NULL;
  30 }
  31
  32 static struct target_type *get_target_type(const char *name)
  33 {
  34         struct target_type *tt;
  35
  36         down_read(&_lock);
  37
  38         tt = __find_target_type(name);
  39         if (tt && !try_module_get(tt->module))
  40                 tt = NULL;
  41
  42         up_read(&_lock);
  43         return tt;
  44 }
  45
  46 static void load_module(const char *name)
  47 {
  48         request_module("dm-%s", name);
  49 }
  50
  51 struct target_type *dm_get_target_type(const char *name)
  52 {
  53         struct target_type *tt = get_target_type(name);
  54
  55         if (!tt) {
  56                 load_module(name);
  57                 tt = get_target_type(name);
  58         }
  59
  60         return tt;
  61 }
  62
  63 void dm_put_target_type(struct target_type *tt)
  64 {
  65         down_read(&_lock);
  66         module_put(tt->module);
  67         up_read(&_lock);
  68 }
  69
  70 int dm_target_iterate(void (*iter_func)(struct target_type *tt,
  71                                         void *param), void *param)
  72 {
  73         struct target_type *tt;
  74
  75         down_read(&_lock);
  76         list_for_each_entry(tt, &_targets, list)
  77                 iter_func(tt, param);
  78         up_read(&_lock);
  79
  80         return 0;
  81 }
  82
  83 int dm_register_target(struct target_type *tt)
  84 {
  85         int rv = 0;
  86
  87         down_write(&_lock);
  88         if (__find_target_type(tt->name))
  89                 rv = -EEXIST;
  90         else
  91                 list_add(&tt->list, &_targets);
  92
  93         up_write(&_lock);
  94         return rv;
  95 }
  96
  97 void dm_unregister_target(struct target_type *tt)
  98 {
  99         down_write(&_lock);
 100         if (!__find_target_type(tt->name)) {
 101                 DMCRIT("Unregistering unrecognised target: %s", tt->name);
 102                 BUG();
 103         }
 104
 105         list_del(&tt->list);
 106
 107         up_write(&_lock);
 108 }
 109
 110 /*
 111  * io-err: always fails an io, useful for bringing
 112  * up LVs that have holes in them.
 113  */
 114 static int io_err_ctr(struct dm_target *tt, unsigned int argc, char **args)
 115 {
 116         /*
 117          * Return error for discards instead of -EOPNOTSUPP
 118          */
 119         tt->num_discard_requests = 1;
 120
 121         return 0;
 122 }
 123
 124 static void io_err_dtr(struct dm_target *tt)
 125 {
 126         /* empty */
 127 }
 128
 129 static int io_err_map(struct dm_target *tt, struct bio *bio,
 130                       union map_info *map_context)
 131 {
 132         return -EIO;
 133 }
 134
 135 static struct target_type error_target = {
 136         .name = "error",
 137         .version = {1, 0, 1},
 138         .ctr  = io_err_ctr,
 139         .dtr  = io_err_dtr,
 140         .map  = io_err_map,
 141 };
 142
 143 int __init dm_target_init(void)
 144 {
 145         return dm_register_target(&error_target);
 146 }
 147
 148 void dm_target_exit(void)
 149 {
 150         dm_unregister_target(&error_target);
 151 }
 152
 153 EXPORT_SYMBOL(dm_register_target);
 154 EXPORT_SYMBOL(dm_unregister_target);