/* * 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");