[linux-2.6-block.git] / drivers / md / dm-zero.c

/*
 * 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 -EIO;
		}
		zero_fill_bio(bio);
		break;
	case REQ_OP_WRITE:
		/* writes get silently dropped */
		break;
	default:
		return -EIO;
	}

	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");
Commit	Line	Data
	1	/*
	2	* Copyright (C) 2003 Jana Saout <jana@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	/*
	26	* Silently drop discards, avoiding -EOPNOTSUPP.
	27	*/
	28	ti->num_discard_bios = 1;
	29
	30	return 0;
	31	}
	32
	33	/*
	34	* Return zeros only on reads
	35	*/
	36	static int zero_map(struct dm_target ti, struct bio bio)
	37	{
	38	switch (bio_op(bio)) {
	39	case REQ_OP_READ:
	40	if (bio->bi_opf & REQ_RAHEAD) {
	41	/* readahead of null bytes only wastes buffer cache */
	42	return -EIO;
	43	}
	44	zero_fill_bio(bio);
	45	break;
	46	case REQ_OP_WRITE:
	47	/* writes get silently dropped */
	48	break;
	49	default:
	50	return -EIO;
	51	}
	52
	53	bio_endio(bio);
	54
	55	/* accepted bio, don't make new request */
	56	return DM_MAPIO_SUBMITTED;
	57	}
	58
	59	static struct target_type zero_target = {
	60	.name = "zero",
	61	.version = {1, 1, 0},
	62	.module = THIS_MODULE,
	63	.ctr = zero_ctr,
	64	.map = zero_map,
	65	};
	66
	67	static int __init dm_zero_init(void)
	68	{
	69	int r = dm_register_target(&zero_target);
	70
	71	if (r < 0)
	72	DMERR("register failed %d", r);
	73
	74	return r;
	75	}
	76
	77	static void __exit dm_zero_exit(void)
	78	{
	79	dm_unregister_target(&zero_target);
	80	}
	81
	82	module_init(dm_zero_init)
	83	module_exit(dm_zero_exit)
	84
	85	MODULE_AUTHOR("Jana Saout <jana@saout.de>");
	86	MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
	87	MODULE_LICENSE("GPL");