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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;
};
/*
* If a path selector uses this flag, a high resolution timer is used
* (via ktime_get_ns) to account for IO start time in BIO-based mpath.
* This improves performance of some path selectors (i.e. HST), in
* exchange for slightly higher overhead when submitting the BIO.
* The extra cost is usually offset by improved path selection for
* some benchmarks.
*
* This has no effect for request-based mpath, since it already uses a
* higher precision timer by default.
*/
#define DM_PS_USE_HR_TIMER 0x00000001
#define dm_ps_use_hr_timer(type) ((type)->features & DM_PS_USE_HR_TIMER)
/* Information about a path selector type */
struct path_selector_type {
char *name;
struct module *module;
unsigned int features;
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.
*/
struct dm_path *(*select_path) (struct path_selector *ps,
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, u64 start_time);
};
/* 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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