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 #define DM_MSG_PREFIX "zero"
14
15 /*
16 * Construct a dummy mapping that only returns zeros
17 */
18 static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv)
19 {
20 if (argc != 0) {
21 ti->error = "No arguments required";
22 return -EINVAL;
23 }
24
25 return 0;
26 }
27
28 /*
29 * Return zeros only on reads
30 */
31 static int zero_map(struct dm_target *ti, struct bio *bio,
32 union map_info *map_context)
33 {
34 switch(bio_rw(bio)) {
35 case READ:
36 zero_fill_bio(bio);
37 break;
38 case READA:
39 /* readahead of null bytes only wastes buffer cache */
40 return -EIO;
41 case WRITE:
42 /* writes get silently dropped */
43 break;
44 }
45
46 bio_endio(bio, 0);
47
48 /* accepted bio, don't make new request */
49 return DM_MAPIO_SUBMITTED;
50 }
51
52 static struct target_type zero_target = {
53 .name = "zero",
54 .version = {1, 0, 0},
55 .module = THIS_MODULE,
56 .ctr = zero_ctr,
57 .map = zero_map,
58 };
59
60 static int __init dm_zero_init(void)
61 {
62 int r = dm_register_target(&zero_target);
63
64 if (r < 0)
65 DMERR("register failed %d", r);
66
67 return r;
68 }
69
70 static void __exit dm_zero_exit(void)
71 {
72 int r = dm_unregister_target(&zero_target);
73
74 if (r < 0)
75 DMERR("unregister failed %d", r);
76 }
77
78 module_init(dm_zero_init)
79 module_exit(dm_zero_exit)
80
81 MODULE_AUTHOR("Christophe Saout <christophe@saout.de>");
82 MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
83 MODULE_LICENSE("GPL");
84
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