linux-hardened/drivers/md/dm-path-selector.h
Kiyoshi Ueda 02ab823fd1 dm mpath: add start_io and nr_bytes to path selectors
This patch makes two additions to the dm path selector interface for
dynamic load balancers:
  o a new hook, start_io()
  o a new parameter 'nr_bytes' to select_path()/start_io()/end_io()
    to pass the size of the I/O

start_io() is called when a target driver actually submits I/O
to the selected path.
Path selectors can use it to start accounting of the I/O.
(e.g. counting the number of in-flight I/Os.)
The start_io hook is based on the patch posted by Stefan Bader:
https://www.redhat.com/archives/dm-devel/2005-October/msg00050.html

nr_bytes, the size of the I/O, is so path selectors can take the
size of the I/O into account when deciding which path to use.
dm-service-time uses it to estimate service time, for example.
(Added the nr_bytes member to dm_mpath_io instead of using existing
 details.bi_size, since request-based dm patch deletes it.)

Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2009-06-22 10:12:27 +01:00

97 lines
2.5 KiB
C

/*
* 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