89 lines
1.6 KiB
C
89 lines
1.6 KiB
C
|
/*
|
||
|
|
* Copyright (C) 2003 Jana Saout <jana@saout.de>
|
||
|
|
*
|
||
|
|
* This file is released under the GPL.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#include <linux/device-mapper.h>
|
||
|
|
|
||
|
|
#include <linux/module.h>
|
||
|
|
#include <linux/init.h>
|
||
|
|
#include <linux/bio.h>
|
||
|
|
|
||
|
|
#define DM_MSG_PREFIX "zero"
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Construct a dummy mapping that only returns zeros
|
||
|
|
*/
|
||
|
|
static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv)
|
||
|
|
{
|
||
|
|
if (argc != 0) {
|
||
|
|
ti->error = "No arguments required";
|
||
|
|
return -EINVAL;
|
||
|
|
}
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Silently drop discards, avoiding -EOPNOTSUPP.
|
||
|
|
*/
|
||
|
|
ti->num_discard_bios = 1;
|
||
|
|
|
||
|
|
return 0;
|
||
|
|
}
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Return zeros only on reads
|
||
|
|
*/
|
||
|
|
static int zero_map(struct dm_target *ti, struct bio *bio)
|
||
|
|
{
|
||
|
|
switch (bio_op(bio)) {
|
||
|
|
case REQ_OP_READ:
|
||
|
|
if (bio->bi_opf & REQ_RAHEAD) {
|
||
|
|
/* readahead of null bytes only wastes buffer cache */
|
||
|
|
return DM_MAPIO_KILL;
|
||
|
|
}
|
||
|
|
zero_fill_bio(bio);
|
||
|
|
break;
|
||
|
|
case REQ_OP_WRITE:
|
||
|
|
/* writes get silently dropped */
|
||
|
|
break;
|
||
|
|
default:
|
||
|
|
return DM_MAPIO_KILL;
|
||
|
|
}
|
||
|
|
|
||
|
|
bio_endio(bio);
|
||
|
|
|
||
|
|
/* accepted bio, don't make new request */
|
||
|
|
return DM_MAPIO_SUBMITTED;
|
||
|
|
}
|
||
|
|
|
||
|
|
static struct target_type zero_target = {
|
||
|
|
.name = "zero",
|
||
|
|
.version = {1, 1, 0},
|
||
|
|
.features = DM_TARGET_NOWAIT,
|
||
|
|
.module = THIS_MODULE,
|
||
|
|
.ctr = zero_ctr,
|
||
|
|
.map = zero_map,
|
||
|
|
};
|
||
|
|
|
||
|
|
static int __init dm_zero_init(void)
|
||
|
|
{
|
||
|
|
int r = dm_register_target(&zero_target);
|
||
|
|
|
||
|
|
if (r < 0)
|
||
|
|
DMERR("register failed %d", r);
|
||
|
|
|
||
|
|
return r;
|
||
|
|
}
|
||
|
|
|
||
|
|
static void __exit dm_zero_exit(void)
|
||
|
|
{
|
||
|
|
dm_unregister_target(&zero_target);
|
||
|
|
}
|
||
|
|
|
||
|
|
module_init(dm_zero_init)
|
||
|
|
module_exit(dm_zero_exit)
|
||
|
|
|
||
|
|
MODULE_AUTHOR("Jana Saout <jana@saout.de>");
|
||
|
|
MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
|
||
|
|
MODULE_LICENSE("GPL");
|