linux-imx

/*

 * 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},

    .module = THIS_MODULE,

    .ctr    = zero_ctr,