diff options
Diffstat (limited to 'kernel/drivers/md/dm-zero.c')
-rw-r--r-- | kernel/drivers/md/dm-zero.c | 84 |
1 files changed, 84 insertions, 0 deletions
diff --git a/kernel/drivers/md/dm-zero.c b/kernel/drivers/md/dm-zero.c new file mode 100644 index 000000000..b9a64bbce --- /dev/null +++ b/kernel/drivers/md/dm-zero.c @@ -0,0 +1,84 @@ +/* + * 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_rw(bio)) { + case READ: + zero_fill_bio(bio); + break; + case READA: + /* readahead of null bytes only wastes buffer cache */ + return -EIO; + case WRITE: + /* writes get silently dropped */ + break; + } + + bio_endio(bio, 0); + + /* 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"); |