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 ti->discards_supported = true;
31
32 return 0;
33 }
34
35 /*
36 * Return zeros only on reads
37 */
zero_map(struct dm_target * ti,struct bio * bio)38 static 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
zero_io_hints(struct dm_target * ti,struct queue_limits * limits)62 static 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
69 static 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 };
78 module_dm(zero);
79
80 MODULE_AUTHOR("Jana Saout <jana@saout.de>");
81 MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
82 MODULE_LICENSE("GPL");
83