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 */
19static 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 ti->discards_supported = true;
31
32 return 0;
33}
34
35/*
36 * Return zeros only on reads
37 */
38static int zero_map(struct dm_target *ti, struct bio *bio)
39{
40 switch (bio_op(bio)) {
41 case REQ_OP_READ:
42 if (bio->bi_opf & REQ_RAHEAD) {
43 /* readahead of null bytes only wastes buffer cache */
44 return DM_MAPIO_KILL;
45 }
46 zero_fill_bio(bio);
47 break;
48 case REQ_OP_WRITE:
49 case REQ_OP_DISCARD:
50 /* writes get silently dropped */
51 break;
52 default:
53 return DM_MAPIO_KILL;
54 }
55
56 bio_endio(bio);
57
58 /* accepted bio, don't make new request */
59 return DM_MAPIO_SUBMITTED;
60}
61
62static void zero_io_hints(struct dm_target *ti, struct queue_limits *limits)
63{
64 limits->max_hw_discard_sectors = UINT_MAX;
65 limits->discard_granularity = 512;
66}
67
68static struct target_type zero_target = {
69 .name = "zero",
70 .version = {1, 2, 0},
71 .features = DM_TARGET_NOWAIT,
72 .module = THIS_MODULE,
73 .ctr = zero_ctr,
74 .map = zero_map,
75 .io_hints = zero_io_hints,
76};
77module_dm(zero);
78
79MODULE_AUTHOR("Jana Saout <jana@saout.de>");
80MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
81MODULE_LICENSE("GPL");
82