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