dm-target.c

Go to the documentation of this file.

/*
 * Copyright (C) 2001 Sistina Software (UK) Limited
 *
 * This file is released under the GPL.
 */

#include "dm.h"

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kmod.h>
#include <linux/bio.h>

#define DM_MSG_PREFIX "target"

static LIST_HEAD(_targets);
static DECLARE_RWSEM(_lock);

#define DM_MOD_NAME_SIZE 32

static inline struct target_type *__find_target_type(const char *name)
{
    struct target_type *tt;

    list_for_each_entry(tt, &_targets, list)
        if (!strcmp(name, tt->name))
            return tt;

    return NULL;
}

static struct target_type *get_target_type(const char *name)
{
    struct target_type *tt;

    down_read(&_lock);

    tt = __find_target_type(name);
    if (tt && !try_module_get(tt->module))
        tt = NULL;

    up_read(&_lock);
    return tt;
}

static void load_module(const char *name)
{
    request_module("dm-%s", name);
}

struct target_type *dm_get_target_type(const char *name)
{
    struct target_type *tt = get_target_type(name);

    if (!tt) {
        load_module(name);
        tt = get_target_type(name);
    }

    return tt;
}

void dm_put_target_type(struct target_type *tt)
{
    down_read(&_lock);
    module_put(tt->module);
    up_read(&_lock);
}

int dm_target_iterate(void (*iter_func)(struct target_type *tt,
                    void *param), void *param)
{
    struct target_type *tt;

    down_read(&_lock);
    list_for_each_entry(tt, &_targets, list)
        iter_func(tt, param);
    up_read(&_lock);

    return 0;
}

int dm_register_target(struct target_type *tt)
{
    int rv = 0;

    down_write(&_lock);
    if (__find_target_type(tt->name))
        rv = -EEXIST;
    else
        list_add(&tt->list, &_targets);

    up_write(&_lock);
    return rv;
}

void dm_unregister_target(struct target_type *tt)
{
    down_write(&_lock);
    if (!__find_target_type(tt->name)) {
        DMCRIT("Unregistering unrecognised target: %s", tt->name);
        BUG();
    }

    list_del(&tt->list);

    up_write(&_lock);
}

/*
 * io-err: always fails an io, useful for bringing
 * up LVs that have holes in them.
 */
static int io_err_ctr(struct dm_target *tt, unsigned int argc, char **args)
{
    /*
     * Return error for discards instead of -EOPNOTSUPP
     */
    tt->num_discard_requests = 1;

    return 0;
}

static void io_err_dtr(struct dm_target *tt)
{
    /* empty */
}

static int io_err_map(struct dm_target *tt, struct bio *bio,
              union map_info *map_context)
{
    return -EIO;
}

static struct target_type error_target = {
    .name = "error",
    .version = {1, 0, 1},
    .ctr  = io_err_ctr,
    .dtr  = io_err_dtr,
    .map  = io_err_map,
};

int __init dm_target_init(void)
{
    return dm_register_target(&error_target);
}

void dm_target_exit(void)
{
    dm_unregister_target(&error_target);
}

EXPORT_SYMBOL(dm_register_target);
EXPORT_SYMBOL(dm_unregister_target);