[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
3bd94003	1	// SPDX-License-Identifier: GPL-2.0-only
1da177e4	2	/*
bf14299f	3	* Copyright (C) 2003 Jana Saout <jana@saout.de>
1da177e4 LT	4	*
	5	* This file is released under the GPL.
	6	*/
	7
586e80e6	8	#include <linux/device-mapper.h>
1da177e4 LT	9
	10	#include <linux/module.h>
	11	#include <linux/init.h>
	12	#include <linux/bio.h>
	13
72d94861 AK	14	#define DM_MSG_PREFIX "zero"
72d94861 AK	15
1da177e4 LT	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) {
72d94861	22	ti->error = "No arguments required";
1da177e4 LT	23	return -EINVAL;
	24	}
	25
f8facb61 MS	26	/*
	27	* Silently drop discards, avoiding -EOPNOTSUPP.
	28	*/
55a62eef	29	ti->num_discard_bios = 1;
f8facb61	30
1da177e4 LT	31	return 0;
	32	}
	33
	34	/*
	35	* Return zeros only on reads
	36	*/
7de3ee57	37	static int zero_map(struct dm_target ti, struct bio bio)
1da177e4	38	{
70246286 CH	39	switch (bio_op(bio)) {
70246286 CH	40	case REQ_OP_READ:
1eff9d32	41	if (bio->bi_opf & REQ_RAHEAD) {
70246286	42	/* readahead of null bytes only wastes buffer cache */
846785e6	43	return DM_MAPIO_KILL;
70246286	44	}
1da177e4 LT	45	zero_fill_bio(bio);
1da177e4 LT	46	break;
70246286	47	case REQ_OP_WRITE:
1da177e4 LT	48	/* writes get silently dropped */
1da177e4 LT	49	break;
70246286	50	default:
846785e6	51	return DM_MAPIO_KILL;
1da177e4 LT	52	}
1da177e4 LT	53
4246a0b6	54	bio_endio(bio);
1da177e4 LT	55
1da177e4 LT	56	/* accepted bio, don't make new request */
d2a7ad29	57	return DM_MAPIO_SUBMITTED;
1da177e4 LT	58	}
	59
	60	static struct target_type zero_target = {
	61	.name = "zero",
7de3ee57	62	.version = {1, 1, 0},
410fe220	63	.features = DM_TARGET_NOWAIT,
1da177e4 LT	64	.module = THIS_MODULE,
	65	.ctr = zero_ctr,
	66	.map = zero_map,
	67	};
	68
5e198d94	69	static int __init dm_zero_init(void)
1da177e4 LT	70	{
	71	int r = dm_register_target(&zero_target);
	72
	73	if (r < 0)
72d94861	74	DMERR("register failed %d", r);
1da177e4 LT	75
	76	return r;
	77	}
	78
5e198d94	79	static void __exit dm_zero_exit(void)
1da177e4	80	{
10d3bd09	81	dm_unregister_target(&zero_target);
1da177e4 LT	82	}
	83
	84	module_init(dm_zero_init)
	85	module_exit(dm_zero_exit)
	86
bf14299f	87	MODULE_AUTHOR("Jana Saout <jana@saout.de>");
1da177e4 LT	88	MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
1da177e4 LT	89	MODULE_LICENSE("GPL");