1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (C) 2003 Jana Saout <jana@saout.de>
4 *
5 * This file is released under the GPL.
6 */
7
8 #include <linux/device-mapper.h>
9
10 #include <linux/module.h>
11 #include <linux/init.h>
12 #include <linux/bio.h>
13
14 #define DM_MSG_PREFIX "zero"
15
16 /*
17 * Construct a dummy mapping that only returns zeros
18 */
zero_ctr(struct dm_target * ti,unsigned int argc,char ** argv)19 static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv)
20 {
21 if (argc != 0) {
22 ti->error = "No arguments required";
23 return -EINVAL;
24 }
25
26 /*
27 * Silently drop discards, avoiding -EOPNOTSUPP.
28 */
29 ti->num_discard_bios = 1;
30
31 return 0;
32 }
33
34 /*
35 * Return zeros only on reads
36 */
zero_map(struct dm_target * ti,struct bio * bio)37 static int zero_map(struct dm_target *ti, struct bio *bio)
38 {
39 switch (bio_op(bio)) {
40 case REQ_OP_READ:
41 if (bio->bi_opf & REQ_RAHEAD) {
42 /* readahead of null bytes only wastes buffer cache */
43 return DM_MAPIO_KILL;
44 }
45 zero_fill_bio(bio);
46 break;
47 case REQ_OP_WRITE:
48 /* writes get silently dropped */
49 break;
50 default:
51 return DM_MAPIO_KILL;
52 }
53
54 bio_endio(bio);
55
56 /* accepted bio, don't make new request */
57 return DM_MAPIO_SUBMITTED;
58 }
59
60 static struct target_type zero_target = {
61 .name = "zero",
62 .version = {1, 1, 0},
63 .features = DM_TARGET_NOWAIT,
64 .module = THIS_MODULE,
65 .ctr = zero_ctr,
66 .map = zero_map,
67 };
68
dm_zero_init(void)69 static int __init dm_zero_init(void)
70 {
71 int r = dm_register_target(&zero_target);
72
73 if (r < 0)
74 DMERR("register failed %d", r);
75
76 return r;
77 }
78
dm_zero_exit(void)79 static void __exit dm_zero_exit(void)
80 {
81 dm_unregister_target(&zero_target);
82 }
83
84 module_init(dm_zero_init)
85 module_exit(dm_zero_exit)
86
87 MODULE_AUTHOR("Jana Saout <jana@saout.de>");
88 MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
89 MODULE_LICENSE("GPL");
90