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

// SPDX-License-Identifier: GPL-2.0-only
/*
 * 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},
	.features = DM_TARGET_NOWAIT,
	.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	// SPDX-License-Identifier: GPL-2.0-only
	2	/*
	3	* Copyright (C) 2003 Jana Saout <jana@saout.de>
	4	*
	5	* This file is released under the GPL.
	6	*/
	7
	8	#include <linux/device-mapper.h>
	9
	10	#include <linux/module.h>
	11	#include <linux/init.h>
	12	#include <linux/bio.h>
	13
	14	#define DM_MSG_PREFIX "zero"
	15
	16	/*
	17	* Construct a dummy mapping that only returns zeros
	18	*/
	19	static int zero_ctr(struct dm_target ti, unsigned int argc, char *argv)
	20	{
	21	if (argc != 0) {
	22	ti->error = "No arguments required";
	23	return -EINVAL;
	24	}
	25
	26	/*
	27	* Silently drop discards, avoiding -EOPNOTSUPP.
	28	*/
	29	ti->num_discard_bios = 1;
	30
	31	return 0;
	32	}
	33
	34	/*
	35	* Return zeros only on reads
	36	*/
	37	static int zero_map(struct dm_target ti, struct bio bio)
	38	{
	39	switch (bio_op(bio)) {
	40	case REQ_OP_READ:
	41	if (bio->bi_opf & REQ_RAHEAD) {
	42	/* readahead of null bytes only wastes buffer cache */
	43	return DM_MAPIO_KILL;
	44	}
	45	zero_fill_bio(bio);
	46	break;
	47	case REQ_OP_WRITE:
	48	/* writes get silently dropped */
	49	break;
	50	default:
	51	return DM_MAPIO_KILL;
	52	}
	53
	54	bio_endio(bio);
	55
	56	/* accepted bio, don't make new request */
	57	return DM_MAPIO_SUBMITTED;
	58	}
	59
	60	static struct target_type zero_target = {
	61	.name = "zero",
	62	.version = {1, 1, 0},
	63	.features = DM_TARGET_NOWAIT,
	64	.module = THIS_MODULE,
	65	.ctr = zero_ctr,
	66	.map = zero_map,
	67	};
	68
	69	static int __init dm_zero_init(void)
	70	{
	71	int r = dm_register_target(&zero_target);
	72
	73	if (r < 0)
	74	DMERR("register failed %d", r);
	75
	76	return r;
	77	}
	78
	79	static void __exit dm_zero_exit(void)
	80	{
	81	dm_unregister_target(&zero_target);
	82	}
	83
	84	module_init(dm_zero_init)
	85	module_exit(dm_zero_exit)
	86
	87	MODULE_AUTHOR("Jana Saout <jana@saout.de>");
	88	MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
	89	MODULE_LICENSE("GPL");