1/*
 2 * Copyright (C) 2003 Jana Saout <jana@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_bios = 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{
38	switch (bio_op(bio)) {
39	case REQ_OP_READ:
40		if (bio->bi_opf & REQ_RAHEAD) {
41			/* readahead of null bytes only wastes buffer cache */
42			return DM_MAPIO_KILL;
43		}
44		zero_fill_bio(bio);
45		break;
46	case REQ_OP_WRITE:
 
 
 
47		/* writes get silently dropped */
48		break;
49	default:
50		return DM_MAPIO_KILL;
51	}
52
53	bio_endio(bio);
54
55	/* accepted bio, don't make new request */
56	return DM_MAPIO_SUBMITTED;
57}
58
59static struct target_type zero_target = {
60	.name   = "zero",
61	.version = {1, 1, 0},
62	.features = DM_TARGET_NOWAIT,
63	.module = THIS_MODULE,
64	.ctr    = zero_ctr,
65	.map    = zero_map,
66};
67
68static int __init dm_zero_init(void)
69{
70	int r = dm_register_target(&zero_target);
71
72	if (r < 0)
73		DMERR("register failed %d", r);
74
75	return r;
76}
77
78static void __exit dm_zero_exit(void)
79{
80	dm_unregister_target(&zero_target);
81}
82
83module_init(dm_zero_init)
84module_exit(dm_zero_exit)
85
86MODULE_AUTHOR("Jana Saout <jana@saout.de>");
87MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
88MODULE_LICENSE("GPL");

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