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1da177e4 LT |
1 | /* |
2 | * Copyright (C) 2003 Christophe Saout <christophe@saout.de> | |
3 | * | |
4 | * This file is released under the GPL. | |
5 | */ | |
6 | ||
586e80e6 | 7 | #include <linux/device-mapper.h> |
1da177e4 LT |
8 | |
9 | #include <linux/module.h> | |
10 | #include <linux/init.h> | |
11 | #include <linux/bio.h> | |
12 | ||
72d94861 AK |
13 | #define DM_MSG_PREFIX "zero" |
14 | ||
1da177e4 LT |
15 | /* |
16 | * Construct a dummy mapping that only returns zeros | |
17 | */ | |
18 | static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv) | |
19 | { | |
20 | if (argc != 0) { | |
72d94861 | 21 | ti->error = "No arguments required"; |
1da177e4 LT |
22 | return -EINVAL; |
23 | } | |
24 | ||
f8facb61 MS |
25 | /* |
26 | * Silently drop discards, avoiding -EOPNOTSUPP. | |
27 | */ | |
28 | ti->num_discard_requests = 1; | |
29 | ||
1da177e4 LT |
30 | return 0; |
31 | } | |
32 | ||
33 | /* | |
34 | * Return zeros only on reads | |
35 | */ | |
36 | static int zero_map(struct dm_target *ti, struct bio *bio, | |
37 | union map_info *map_context) | |
38 | { | |
39 | switch(bio_rw(bio)) { | |
40 | case READ: | |
41 | zero_fill_bio(bio); | |
42 | break; | |
43 | case READA: | |
44 | /* readahead of null bytes only wastes buffer cache */ | |
45 | return -EIO; | |
46 | case WRITE: | |
47 | /* writes get silently dropped */ | |
48 | break; | |
49 | } | |
50 | ||
6712ecf8 | 51 | bio_endio(bio, 0); |
1da177e4 LT |
52 | |
53 | /* accepted bio, don't make new request */ | |
d2a7ad29 | 54 | return DM_MAPIO_SUBMITTED; |
1da177e4 LT |
55 | } |
56 | ||
57 | static struct target_type zero_target = { | |
58 | .name = "zero", | |
59 | .version = {1, 0, 0}, | |
60 | .module = THIS_MODULE, | |
61 | .ctr = zero_ctr, | |
62 | .map = zero_map, | |
63 | }; | |
64 | ||
5e198d94 | 65 | static int __init dm_zero_init(void) |
1da177e4 LT |
66 | { |
67 | int r = dm_register_target(&zero_target); | |
68 | ||
69 | if (r < 0) | |
72d94861 | 70 | DMERR("register failed %d", r); |
1da177e4 LT |
71 | |
72 | return r; | |
73 | } | |
74 | ||
5e198d94 | 75 | static void __exit dm_zero_exit(void) |
1da177e4 | 76 | { |
10d3bd09 | 77 | dm_unregister_target(&zero_target); |
1da177e4 LT |
78 | } |
79 | ||
80 | module_init(dm_zero_init) | |
81 | module_exit(dm_zero_exit) | |
82 | ||
83 | MODULE_AUTHOR("Christophe Saout <christophe@saout.de>"); | |
84 | MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros"); | |
85 | MODULE_LICENSE("GPL"); |