Root/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
16static LIST_HEAD(_targets);
17static DECLARE_RWSEM(_lock);
18
19#define DM_MOD_NAME_SIZE 32
20
21static 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
32static 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
46static void load_module(const char *name)
47{
48    request_module("dm-%s", name);
49}
50
51struct 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
63void dm_put_target_type(struct target_type *tt)
64{
65    down_read(&_lock);
66    module_put(tt->module);
67    up_read(&_lock);
68}
69
70int 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
83int 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
97void 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 */
114static 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_bios = 1;
120
121    return 0;
122}
123
124static void io_err_dtr(struct dm_target *tt)
125{
126    /* empty */
127}
128
129static int io_err_map(struct dm_target *tt, struct bio *bio)
130{
131    return -EIO;
132}
133
134static struct target_type error_target = {
135    .name = "error",
136    .version = {1, 1, 0},
137    .ctr = io_err_ctr,
138    .dtr = io_err_dtr,
139    .map = io_err_map,
140};
141
142int __init dm_target_init(void)
143{
144    return dm_register_target(&error_target);
145}
146
147void dm_target_exit(void)
148{
149    dm_unregister_target(&error_target);
150}
151
152EXPORT_SYMBOL(dm_register_target);
153EXPORT_SYMBOL(dm_unregister_target);
154

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