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_discard_sectors = UINT_MAX;
65	limits->max_hw_discard_sectors = UINT_MAX;
66	limits->discard_granularity = 512;
67}
68
69static struct target_type zero_target = {
70	.name   = "zero",
71	.version = {1, 2, 0},
72	.features = DM_TARGET_NOWAIT,
73	.module = THIS_MODULE,
74	.ctr    = zero_ctr,
75	.map    = zero_map,
76	.io_hints = zero_io_hints,
77};
78module_dm(zero);
79
80MODULE_AUTHOR("Jana Saout <jana@saout.de>");
81MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
82MODULE_LICENSE("GPL");

 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");