1 /*
2 * Copyright (C) 2003 Christophe Saout <christophe@saout.de>
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/bio.h>
12
13 /*
14 * Construct a dummy mapping that only returns zeros
15 */
16 static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv)
17 {
18 if (argc != 0) {
19 ti->error = "dm-zero: No arguments required";
20 return -EINVAL;
21 }
22
23 return 0;
24 }
25
26 /*
27 * Return zeros only on reads
28 */
29 static int zero_map(struct dm_target *ti, struct bio *bio,
30 union map_info *map_context)
31 {
32 switch(bio_rw(bio)) {
33 case READ:
34 zero_fill_bio(bio);
35 break;
36 case READA:
37 /* readahead of null bytes only wastes buffer cache */
38 return -EIO;
39 case WRITE:
40 /* writes get silently dropped */
41 break;
42 }
43
44 bio_endio(bio, bio->bi_size, 0);
45
46 /* accepted bio, don't make new request */
47 return 0;
48 }
49
50 static struct target_type zero_target = {
51 .name = "zero",
52 .version = {1, 0, 0},
53 .module = THIS_MODULE,
54 .ctr = zero_ctr,
55 .map = zero_map,
56 };
57
58 static int __init dm_zero_init(void)
59 {
60 int r = dm_register_target(&zero_target);
61
62 if (r < 0)
63 DMERR("zero: register failed %d", r);
64
65 return r;
66 }
67
68 static void __exit dm_zero_exit(void)
69 {
70 int r = dm_unregister_target(&zero_target);
71
72 if (r < 0)
73 DMERR("zero: unregister failed %d", r);
74 }
75
76 module_init(dm_zero_init)
77 module_exit(dm_zero_exit)
78
79 MODULE_AUTHOR("Christophe Saout <christophe@saout.de>");
80 MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
81 MODULE_LICENSE("GPL");
82
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