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/kmod.h>
  11 #include <linux/bio.h>
  12 #include <linux/slab.h>
  13
  14 struct tt_internal {
  15         struct target_type tt;
  16
  17         struct list_head list;
  18         long use;
  19 };
  20
  21 static LIST_HEAD(_targets);
  22 static DECLARE_RWSEM(_lock);
  23
  24 #define DM_MOD_NAME_SIZE 32
  25
  26 static inline struct tt_internal *__find_target_type(const char *name)
  27 {
  28         struct list_head *tih;
  29         struct tt_internal *ti;
  30
  31         list_for_each(tih, &_targets) {
  32                 ti = list_entry(tih, struct tt_internal, list);
  33
  34                 if (!strcmp(name, ti->tt.name))
  35                         return ti;
  36         }
  37
  38         return NULL;
  39 }
  40
  41 static struct tt_internal *get_target_type(const char *name)
  42 {
  43         struct tt_internal *ti;
  44
  45         down_read(&_lock);
  46
  47         ti = __find_target_type(name);
  48         if (ti) {
  49                 if ((ti->use == 0) && !try_module_get(ti->tt.module))
  50                         ti = NULL;
  51                 else
  52                         ti->use++;
  53         }
  54
  55         up_read(&_lock);
  56         return ti;
  57 }
  58
  59 static void load_module(const char *name)
  60 {
  61         request_module("dm-%s", name);
  62 }
  63
  64 struct target_type *dm_get_target_type(const char *name)
  65 {
  66         struct tt_internal *ti = get_target_type(name);
  67
  68         if (!ti) {
  69                 load_module(name);
  70                 ti = get_target_type(name);
  71         }
  72
  73         return ti ? &ti->tt : NULL;
  74 }
  75
  76 void dm_put_target_type(struct target_type *t)
  77 {
  78         struct tt_internal *ti = (struct tt_internal *) t;
  79
  80         down_read(&_lock);
  81         if (--ti->use == 0)
  82                 module_put(ti->tt.module);
  83
  84         if (ti->use < 0)
  85                 BUG();
  86         up_read(&_lock);
  87
  88         return;
  89 }
  90
  91 static struct tt_internal *alloc_target(struct target_type *t)
  92 {
  93         struct tt_internal *ti = kmalloc(sizeof(*ti), GFP_KERNEL);
  94
  95         if (ti) {
  96                 memset(ti, 0, sizeof(*ti));
  97                 ti->tt = *t;
  98         }
  99
 100         return ti;
 101 }
 102
 103 int dm_register_target(struct target_type *t)
 104 {
 105         int rv = 0;
 106         struct tt_internal *ti = alloc_target(t);
 107
 108         if (!ti)
 109                 return -ENOMEM;
 110
 111         down_write(&_lock);
 112         if (__find_target_type(t->name))
 113                 rv = -EEXIST;
 114         else
 115                 list_add(&ti->list, &_targets);
 116
 117         up_write(&_lock);
 118         if (rv)
 119                 kfree(ti);
 120         return rv;
 121 }
 122
 123 int dm_unregister_target(struct target_type *t)
 124 {
 125         struct tt_internal *ti;
 126
 127         down_write(&_lock);
 128         if (!(ti = __find_target_type(t->name))) {
 129                 up_write(&_lock);
 130                 return -EINVAL;
 131         }
 132
 133         if (ti->use) {
 134                 up_write(&_lock);
 135                 return -ETXTBSY;
 136         }
 137
 138         list_del(&ti->list);
 139         kfree(ti);
 140
 141         up_write(&_lock);
 142         return 0;
 143 }
 144
 145 /*
 146  * io-err: always fails an io, useful for bringing
 147  * up LVs that have holes in them.
 148  */
 149 static int io_err_ctr(struct dm_target *ti, int argc, char **args)
 150 {
 151         return 0;
 152 }
 153
 154 static void io_err_dtr(struct dm_target *ti)
 155 {
 156         /* empty */
 157 }
 158
 159 static int io_err_map(struct dm_target *ti, struct bio *bio)
 160 {
 161         return -EIO;
 162 }
 163
 164 static struct target_type error_target = {
 165         .name = "error",
 166         .ctr  = io_err_ctr,
 167         .dtr  = io_err_dtr,
 168         .map  = io_err_map,
 169 };
 170
 171 int dm_target_init(void)
 172 {
 173         return dm_register_target(&error_target);
 174 }
 175
 176 void dm_target_exit(void)
 177 {
 178         if (dm_unregister_target(&error_target))
 179                 DMWARN("error target unregistration failed");
 180 }
 181
 182 EXPORT_SYMBOL(dm_register_target);
 183 EXPORT_SYMBOL(dm_unregister_target);