// SPDX-License-Identifier: GPL-2.0-only/* * 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;	ti->discards_supported = true; 	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:	case REQ_OP_DISCARD:		/* 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 void zero_io_hints(struct dm_target *ti, struct queue_limits *limits){	limits->max_hw_discard_sectors = UINT_MAX;	limits->discard_granularity = 512;} static struct target_type zero_target = {	.name   = "zero",	.version = {1, 2, 0},	.features = DM_TARGET_NOWAIT,	.module = THIS_MODULE,	.ctr    = zero_ctr,	.map    = zero_map,	.io_hints = zero_io_hints,};module_dm(zero); MODULE_AUTHOR("Jana Saout <jana@saout.de>");MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");MODULE_LICENSE("GPL");