1/*
2 * Copyright (C) 2003 Jana Saout <jana@saout.de>
3 *
4 * This file is released under the GPL.
5 */
6
7#include <linux/device-mapper.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 */
18static 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 /*
26 * Silently drop discards, avoiding -EOPNOTSUPP.
27 */
28 ti->num_discard_bios = 1;
29
30 return 0;
31}
32
33/*
34 * Return zeros only on reads
35 */
36static int zero_map(struct dm_target *ti, struct bio *bio)
37{
38 switch (bio_op(bio)) {
39 case REQ_OP_READ:
40 if (bio->bi_opf & REQ_RAHEAD) {
41 /* readahead of null bytes only wastes buffer cache */
42 return DM_MAPIO_KILL;
43 }
44 zero_fill_bio(bio);
45 break;
46 case REQ_OP_WRITE:
47 /* writes get silently dropped */
48 break;
49 default:
50 return DM_MAPIO_KILL;
51 }
52
53 bio_endio(bio);
54
55 /* accepted bio, don't make new request */
56 return DM_MAPIO_SUBMITTED;
57}
58
59static struct target_type zero_target = {
60 .name = "zero",
61 .version = {1, 1, 0},
62 .module = THIS_MODULE,
63 .ctr = zero_ctr,
64 .map = zero_map,
65};
66
67static int __init dm_zero_init(void)
68{
69 int r = dm_register_target(&zero_target);
70
71 if (r < 0)
72 DMERR("register failed %d", r);
73
74 return r;
75}
76
77static void __exit dm_zero_exit(void)
78{
79 dm_unregister_target(&zero_target);
80}
81
82module_init(dm_zero_init)
83module_exit(dm_zero_exit)
84
85MODULE_AUTHOR("Jana Saout <jana@saout.de>");
86MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
87MODULE_LICENSE("GPL");
88