1*4882a593Smuzhiyun /*
2*4882a593Smuzhiyun * Copyright (C) 2003 Jana Saout <jana@saout.de>
3*4882a593Smuzhiyun *
4*4882a593Smuzhiyun * This file is released under the GPL.
5*4882a593Smuzhiyun */
6*4882a593Smuzhiyun
7*4882a593Smuzhiyun #include <linux/device-mapper.h>
8*4882a593Smuzhiyun
9*4882a593Smuzhiyun #include <linux/module.h>
10*4882a593Smuzhiyun #include <linux/init.h>
11*4882a593Smuzhiyun #include <linux/bio.h>
12*4882a593Smuzhiyun
13*4882a593Smuzhiyun #define DM_MSG_PREFIX "zero"
14*4882a593Smuzhiyun
15*4882a593Smuzhiyun /*
16*4882a593Smuzhiyun * Construct a dummy mapping that only returns zeros
17*4882a593Smuzhiyun */
zero_ctr(struct dm_target * ti,unsigned int argc,char ** argv)18*4882a593Smuzhiyun static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv)
19*4882a593Smuzhiyun {
20*4882a593Smuzhiyun if (argc != 0) {
21*4882a593Smuzhiyun ti->error = "No arguments required";
22*4882a593Smuzhiyun return -EINVAL;
23*4882a593Smuzhiyun }
24*4882a593Smuzhiyun
25*4882a593Smuzhiyun /*
26*4882a593Smuzhiyun * Silently drop discards, avoiding -EOPNOTSUPP.
27*4882a593Smuzhiyun */
28*4882a593Smuzhiyun ti->num_discard_bios = 1;
29*4882a593Smuzhiyun
30*4882a593Smuzhiyun return 0;
31*4882a593Smuzhiyun }
32*4882a593Smuzhiyun
33*4882a593Smuzhiyun /*
34*4882a593Smuzhiyun * Return zeros only on reads
35*4882a593Smuzhiyun */
zero_map(struct dm_target * ti,struct bio * bio)36*4882a593Smuzhiyun static int zero_map(struct dm_target *ti, struct bio *bio)
37*4882a593Smuzhiyun {
38*4882a593Smuzhiyun switch (bio_op(bio)) {
39*4882a593Smuzhiyun case REQ_OP_READ:
40*4882a593Smuzhiyun if (bio->bi_opf & REQ_RAHEAD) {
41*4882a593Smuzhiyun /* readahead of null bytes only wastes buffer cache */
42*4882a593Smuzhiyun return DM_MAPIO_KILL;
43*4882a593Smuzhiyun }
44*4882a593Smuzhiyun zero_fill_bio(bio);
45*4882a593Smuzhiyun break;
46*4882a593Smuzhiyun case REQ_OP_WRITE:
47*4882a593Smuzhiyun /* writes get silently dropped */
48*4882a593Smuzhiyun break;
49*4882a593Smuzhiyun default:
50*4882a593Smuzhiyun return DM_MAPIO_KILL;
51*4882a593Smuzhiyun }
52*4882a593Smuzhiyun
53*4882a593Smuzhiyun bio_endio(bio);
54*4882a593Smuzhiyun
55*4882a593Smuzhiyun /* accepted bio, don't make new request */
56*4882a593Smuzhiyun return DM_MAPIO_SUBMITTED;
57*4882a593Smuzhiyun }
58*4882a593Smuzhiyun
59*4882a593Smuzhiyun static struct target_type zero_target = {
60*4882a593Smuzhiyun .name = "zero",
61*4882a593Smuzhiyun .version = {1, 1, 0},
62*4882a593Smuzhiyun .module = THIS_MODULE,
63*4882a593Smuzhiyun .ctr = zero_ctr,
64*4882a593Smuzhiyun .map = zero_map,
65*4882a593Smuzhiyun };
66*4882a593Smuzhiyun
dm_zero_init(void)67*4882a593Smuzhiyun static int __init dm_zero_init(void)
68*4882a593Smuzhiyun {
69*4882a593Smuzhiyun int r = dm_register_target(&zero_target);
70*4882a593Smuzhiyun
71*4882a593Smuzhiyun if (r < 0)
72*4882a593Smuzhiyun DMERR("register failed %d", r);
73*4882a593Smuzhiyun
74*4882a593Smuzhiyun return r;
75*4882a593Smuzhiyun }
76*4882a593Smuzhiyun
dm_zero_exit(void)77*4882a593Smuzhiyun static void __exit dm_zero_exit(void)
78*4882a593Smuzhiyun {
79*4882a593Smuzhiyun dm_unregister_target(&zero_target);
80*4882a593Smuzhiyun }
81*4882a593Smuzhiyun
82*4882a593Smuzhiyun module_init(dm_zero_init)
83*4882a593Smuzhiyun module_exit(dm_zero_exit)
84*4882a593Smuzhiyun
85*4882a593Smuzhiyun MODULE_AUTHOR("Jana Saout <jana@saout.de>");
86*4882a593Smuzhiyun MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
87*4882a593Smuzhiyun MODULE_LICENSE("GPL");
88