dm-path-selector.h

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/*
 * 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,
                    size_t nr_bytes);

    /*
     * 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 (*start_io) (struct path_selector *ps, struct dm_path *path,
             size_t nr_bytes);
    int (*end_io) (struct path_selector *ps, struct dm_path *path,
               size_t nr_bytes);
};

/* 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