// 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_discard_sectors = UINT_MAX; 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");