| /* |
| * 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"); |