1// SPDX-License-Identifier: GPL-2.0-only 2/* 3 * Copyright (C) 2003 Jana Saout <jana@saout.de> 4 * 5 * This file is released under the GPL. 6 */ 7 8#include <linux/device-mapper.h> 9 10#include <linux/module.h> 11#include <linux/init.h> 12#include <linux/bio.h> 13 14#define DM_MSG_PREFIX "zero" 15 16/* 17 * Construct a dummy mapping that only returns zeros 18 */ 19static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv) 20{ 21 if (argc != 0) { 22 ti->error = "No arguments required"; 23 return -EINVAL; 24 } 25 26 /* 27 * Silently drop discards, avoiding -EOPNOTSUPP. 28 */ 29 ti->num_discard_bios = 1; 30 ti->discards_supported = true; 31 32 return 0; 33} 34 35/* 36 * Return zeros only on reads 37 */ 38static int zero_map(struct dm_target *ti, struct bio *bio) 39{ 40 switch (bio_op(bio)) { 41 case REQ_OP_READ: 42 if (bio->bi_opf & REQ_RAHEAD) { 43 /* readahead of null bytes only wastes buffer cache */ 44 return DM_MAPIO_KILL; 45 } 46 zero_fill_bio(bio); 47 break; 48 case REQ_OP_WRITE: 49 case REQ_OP_DISCARD: 50 /* writes get silently dropped */ 51 break; 52 default: 53 return DM_MAPIO_KILL; 54 } 55 56 bio_endio(bio); 57 58 /* accepted bio, don't make new request */ 59 return DM_MAPIO_SUBMITTED; 60} 61 62static void zero_io_hints(struct dm_target *ti, struct queue_limits *limits) 63{ 64 limits->max_discard_sectors = UINT_MAX; 65 limits->max_hw_discard_sectors = UINT_MAX; 66 limits->discard_granularity = 512; 67} 68 69static struct target_type zero_target = { 70 .name = "zero", 71 .version = {1, 2, 0}, 72 .features = DM_TARGET_NOWAIT, 73 .module = THIS_MODULE, 74 .ctr = zero_ctr, 75 .map = zero_map, 76 .io_hints = zero_io_hints, 77}; 78module_dm(zero); 79 80MODULE_AUTHOR("Jana Saout <jana@saout.de>"); 81MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros"); 82MODULE_LICENSE("GPL"); 83