dm-zero.c
1.51 KB
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/*
* Copyright (C) 2003 Christophe Saout <christophe@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_rw(bio)) {
case READ:
zero_fill_bio(bio);
break;
case READA:
/* readahead of null bytes only wastes buffer cache */
return -EIO;
case WRITE:
/* writes get silently dropped */
break;
}
bio_endio(bio, 0);
/* accepted bio, don't make new request */
return DM_MAPIO_SUBMITTED;
}
static struct target_type zero_target = {
.name = "zero",
.version = {1, 1, 0},
.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("Christophe Saout <christophe@saout.de>");
MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
MODULE_LICENSE("GPL");