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dm-path-selector.h

/*
 * Copyright (C) 2003 Sistina Software.
 * Copyright (C) 2004 Red Hat, Inc. All rights reserved.
 *
 * Module Author: Heinz Mauelshagen
 *
 * This file is released under the GPL.
 *
 * Path-Selector registration.
 */

#ifndef     DM_PATH_SELECTOR_H
#define     DM_PATH_SELECTOR_H

#include <linux/device-mapper.h>

#include "dm-mpath.h"

/*
 * We provide an abstraction for the code that chooses which path
 * to send some io down.
 */
struct path_selector_type;
struct path_selector {
      struct path_selector_type *type;
      void *context;
};

/* Information about a path selector type */
struct path_selector_type {
      char *name;
      struct module *module;

      unsigned int table_args;
      unsigned int info_args;

      /*
       * Constructs a path selector object, takes custom arguments
       */
      int (*create) (struct path_selector *ps, unsigned argc, char **argv);
      void (*destroy) (struct path_selector *ps);

      /*
       * Add an opaque path object, along with some selector specific
       * path args (eg, path priority).
       */
      int (*add_path) (struct path_selector *ps, struct dm_path *path,
                   int argc, char **argv, char **error);

      /*
       * Chooses a path for this io, if no paths are available then
       * NULL will be returned.
       *
       * repeat_count is the number of times to use the path before
       * calling the function again.  0 means don't call it again unless
       * the path fails.
       */
      struct dm_path *(*select_path) (struct path_selector *ps,
                             unsigned *repeat_count);

      /*
       * Notify the selector that a path has failed.
       */
      void (*fail_path) (struct path_selector *ps, struct dm_path *p);

      /*
       * Ask selector to reinstate a path.
       */
      int (*reinstate_path) (struct path_selector *ps, struct dm_path *p);

      /*
       * Table content based on parameters added in ps_add_path_fn
       * or path selector status
       */
      int (*status) (struct path_selector *ps, struct dm_path *path,
                   status_type_t type, char *result, unsigned int maxlen);

      int (*end_io) (struct path_selector *ps, struct dm_path *path);
};

/* Register a path selector */
int dm_register_path_selector(struct path_selector_type *type);

/* Unregister a path selector */
int dm_unregister_path_selector(struct path_selector_type *type);

/* Returns a registered path selector type */
struct path_selector_type *dm_get_path_selector(const char *name);

/* Releases a path selector  */
void dm_put_path_selector(struct path_selector_type *pst);

#endif

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