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 */
zero_ctr(struct dm_target * ti,unsigned int argc,char ** argv)18 static 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 */
zero_map(struct dm_target * ti,struct bio * bio)36 static 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
59 static 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
dm_zero_init(void)68 static 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
dm_zero_exit(void)78 static void __exit dm_zero_exit(void)
79 {
80 dm_unregister_target(&zero_target);
81 }
82
83 module_init(dm_zero_init)
84 module_exit(dm_zero_exit)
85
86 MODULE_AUTHOR("Jana Saout <jana@saout.de>");
87 MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
88 MODULE_LICENSE("GPL");
89
