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dm-target.c

/*
 * 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>
#include <linux/slab.h>

#define DM_MSG_PREFIX "target"

struct tt_internal {
      struct target_type tt;

      struct list_head list;
      long use;
};

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

#define DM_MOD_NAME_SIZE 32

static inline struct tt_internal *__find_target_type(const char *name)
{
      struct tt_internal *ti;

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

      return NULL;
}

static struct tt_internal *get_target_type(const char *name)
{
      struct tt_internal *ti;

      down_read(&_lock);

      ti = __find_target_type(name);
      if (ti) {
            if ((ti->use == 0) && !try_module_get(ti->tt.module))
                  ti = NULL;
            else
                  ti->use++;
      }

      up_read(&_lock);
      return ti;
}

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

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

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

      return ti ? &ti->tt : NULL;
}

void dm_put_target_type(struct target_type *t)
{
      struct tt_internal *ti = (struct tt_internal *) t;

      down_read(&_lock);
      if (--ti->use == 0)
            module_put(ti->tt.module);

      BUG_ON(ti->use < 0);
      up_read(&_lock);

      return;
}

static struct tt_internal *alloc_target(struct target_type *t)
{
      struct tt_internal *ti = kzalloc(sizeof(*ti), GFP_KERNEL);

      if (ti)
            ti->tt = *t;

      return ti;
}


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

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

      return 0;
}

int dm_register_target(struct target_type *t)
{
      int rv = 0;
      struct tt_internal *ti = alloc_target(t);

      if (!ti)
            return -ENOMEM;

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

      up_write(&_lock);
      if (rv)
            kfree(ti);
      return rv;
}

int dm_unregister_target(struct target_type *t)
{
      struct tt_internal *ti;

      down_write(&_lock);
      if (!(ti = __find_target_type(t->name))) {
            up_write(&_lock);
            return -EINVAL;
      }

      if (ti->use) {
            up_write(&_lock);
            return -ETXTBSY;
      }

      list_del(&ti->list);
      kfree(ti);

      up_write(&_lock);
      return 0;
}

/*
 * io-err: always fails an io, useful for bringing
 * up LVs that have holes in them.
 */
static int io_err_ctr(struct dm_target *ti, unsigned int argc, char **args)
{
      return 0;
}

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

static int io_err_map(struct dm_target *ti, 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)
{
      if (dm_unregister_target(&error_target))
            DMWARN("error target unregistration failed");
}

EXPORT_SYMBOL(dm_register_target);
EXPORT_SYMBOL(dm_unregister_target);

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