Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
1/*
2 * Copyright (C) 2003 Christophe Saout <christophe@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_requests = 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 union map_info *map_context)
38{
39 switch(bio_rw(bio)) {
40 case READ:
41 zero_fill_bio(bio);
42 break;
43 case READA:
44 /* readahead of null bytes only wastes buffer cache */
45 return -EIO;
46 case WRITE:
47 /* writes get silently dropped */
48 break;
49 }
50
51 bio_endio(bio, 0);
52
53 /* accepted bio, don't make new request */
54 return DM_MAPIO_SUBMITTED;
55}
56
57static struct target_type zero_target = {
58 .name = "zero",
59 .version = {1, 0, 0},
60 .module = THIS_MODULE,
61 .ctr = zero_ctr,
62 .map = zero_map,
63};
64
65static int __init dm_zero_init(void)
66{
67 int r = dm_register_target(&zero_target);
68
69 if (r < 0)
70 DMERR("register failed %d", r);
71
72 return r;
73}
74
75static void __exit dm_zero_exit(void)
76{
77 dm_unregister_target(&zero_target);
78}
79
80module_init(dm_zero_init)
81module_exit(dm_zero_exit)
82
83MODULE_AUTHOR("Christophe Saout <christophe@saout.de>");
84MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
85MODULE_LICENSE("GPL");