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02ab823fd1
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>
97 lines
2.5 KiB
C
97 lines
2.5 KiB
C
/*
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* Copyright (C) 2003 Sistina Software.
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* Copyright (C) 2004 Red Hat, Inc. All rights reserved.
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*
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* Module Author: Heinz Mauelshagen
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*
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* This file is released under the GPL.
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*
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* Path-Selector registration.
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*/
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#ifndef DM_PATH_SELECTOR_H
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#define DM_PATH_SELECTOR_H
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#include <linux/device-mapper.h>
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#include "dm-mpath.h"
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/*
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* We provide an abstraction for the code that chooses which path
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* to send some io down.
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*/
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struct path_selector_type;
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struct path_selector {
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struct path_selector_type *type;
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void *context;
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};
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/* Information about a path selector type */
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struct path_selector_type {
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char *name;
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struct module *module;
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unsigned int table_args;
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unsigned int info_args;
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/*
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* Constructs a path selector object, takes custom arguments
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*/
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int (*create) (struct path_selector *ps, unsigned argc, char **argv);
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void (*destroy) (struct path_selector *ps);
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/*
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* Add an opaque path object, along with some selector specific
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* path args (eg, path priority).
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*/
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int (*add_path) (struct path_selector *ps, struct dm_path *path,
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int argc, char **argv, char **error);
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/*
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* Chooses a path for this io, if no paths are available then
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* NULL will be returned.
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*
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* repeat_count is the number of times to use the path before
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* calling the function again. 0 means don't call it again unless
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* the path fails.
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*/
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struct dm_path *(*select_path) (struct path_selector *ps,
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unsigned *repeat_count,
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size_t nr_bytes);
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/*
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* Notify the selector that a path has failed.
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*/
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void (*fail_path) (struct path_selector *ps, struct dm_path *p);
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/*
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* Ask selector to reinstate a path.
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*/
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int (*reinstate_path) (struct path_selector *ps, struct dm_path *p);
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/*
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* Table content based on parameters added in ps_add_path_fn
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* or path selector status
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*/
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int (*status) (struct path_selector *ps, struct dm_path *path,
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status_type_t type, char *result, unsigned int maxlen);
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int (*start_io) (struct path_selector *ps, struct dm_path *path,
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size_t nr_bytes);
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int (*end_io) (struct path_selector *ps, struct dm_path *path,
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size_t nr_bytes);
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};
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/* Register a path selector */
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int dm_register_path_selector(struct path_selector_type *type);
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/* Unregister a path selector */
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int dm_unregister_path_selector(struct path_selector_type *type);
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/* Returns a registered path selector type */
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struct path_selector_type *dm_get_path_selector(const char *name);
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/* Releases a path selector */
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void dm_put_path_selector(struct path_selector_type *pst);
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#endif
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