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