/* * 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; 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: /* 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 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("Jana Saout <jana@saout.de>"); MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros"); MODULE_LICENSE("GPL");