1 /* 2 * Copyright (C) 2003 Christophe Saout <christophe@saout.de> 3 * 4 * This file is released under the GPL. 5 */ 6 7 #include <linux/device-mapper.h> 8 9 #include <linux/module.h> 10 #include <linux/init.h> 11 #include <linux/bio.h> 12 13 #define DM_MSG_PREFIX "zero" 14 15 /* 16 * Construct a dummy mapping that only returns zeros 17 */ 18 static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv) 19 { 20 if (argc != 0) { 21 ti->error = "No arguments required"; 22 return -EINVAL; 23 } 24 25 return 0; 26 } 27 28 /* 29 * Return zeros only on reads 30 */ 31 static int zero_map(struct dm_target *ti, struct bio *bio, 32 union map_info *map_context) 33 { 34 switch(bio_rw(bio)) { 35 case READ: 36 zero_fill_bio(bio); 37 break; 38 case READA: 39 /* readahead of null bytes only wastes buffer cache */ 40 return -EIO; 41 case WRITE: 42 /* writes get silently dropped */ 43 break; 44 } 45 46 bio_endio(bio, 0); 47 48 /* accepted bio, don't make new request */ 49 return DM_MAPIO_SUBMITTED; 50 } 51 52 static struct target_type zero_target = { 53 .name = "zero", 54 .version = {1, 0, 0}, 55 .module = THIS_MODULE, 56 .ctr = zero_ctr, 57 .map = zero_map, 58 }; 59 60 static int __init dm_zero_init(void) 61 { 62 int r = dm_register_target(&zero_target); 63 64 if (r < 0) 65 DMERR("register failed %d", r); 66 67 return r; 68 } 69 70 static void __exit dm_zero_exit(void) 71 { 72 dm_unregister_target(&zero_target); 73 } 74 75 module_init(dm_zero_init) 76 module_exit(dm_zero_exit) 77 78 MODULE_AUTHOR("Christophe Saout <christophe@saout.de>"); 79 MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros"); 80 MODULE_LICENSE("GPL"); 81