1 /*
2 * Copyright (C) 2003 Christophe Saout <christophe@saout.de>
3 *
4 * This file is released under the GPL.
5 */
6
7 #include "dm.h"
8
9 #include <linux/module.h>
10 #include <linux/init.h>
11 #include <linux/bio.h>
12
13 /*
14 * Construct a dummy mapping that only returns zeros
15 */
16 static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv)
17 {
18 if (argc != 0) {
19 ti->error = "dm-zero: No arguments required";
20 return -EINVAL;
21 }
22
23 return 0;
24 }
25
26 /*
27 * Fills the bio pages with zeros
28 */
29 static void zero_fill_bio(struct bio *bio)
30 {
31 unsigned long flags;
32 struct bio_vec *bv;
33 int i;
34
35 bio_for_each_segment(bv, bio, i) {
36 char *data = bvec_kmap_irq(bv, &flags);
37 memset(data, 0, bv->bv_len);
38 flush_dcache_page(bv->bv_page);
39 bvec_kunmap_irq(data, &flags);
40 }
41 }
42
43 /*
44 * Return zeros only on reads
45 */
46 static int zero_map(struct dm_target *ti, struct bio *bio,
47 union map_info *map_context)
48 {
49 switch(bio_rw(bio)) {
50 case READ:
51 zero_fill_bio(bio);
52 break;
53 case READA:
54 /* readahead of null bytes only wastes buffer cache */
55 return -EIO;
56 case WRITE:
57 /* writes get silently dropped */
58 break;
59 }
60
61 bio_endio(bio, bio->bi_size, 0);
62
63 /* accepted bio, don't make new request */
64 return 0;
65 }
66
67 static struct target_type zero_target = {
68 .name = "zero",
69 .version = {1, 0, 0},
70 .module = THIS_MODULE,
71 .ctr = zero_ctr,
72 .map = zero_map,
73 };
74
75 int __init dm_zero_init(void)
76 {
77 int r = dm_register_target(&zero_target);
78
79 if (r < 0)
80 DMERR("zero: register failed %d", r);
81
82 return r;
83 }
84
85 void __exit dm_zero_exit(void)
86 {
87 int r = dm_unregister_target(&zero_target);
88
89 if (r < 0)
90 DMERR("zero: unregister failed %d", r);
91 }
92
93 module_init(dm_zero_init)
94 module_exit(dm_zero_exit)
95
96 MODULE_AUTHOR("Christophe Saout <christophe@saout.de>");
97 MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
98 MODULE_LICENSE("GPL");
99
|
This page was automatically generated by the
LXR engine.
|