drivers/md/dm-path-selector.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  * Copyright (C) 2003 Sistina Software.
   4  * Copyright (C) 2004 Red Hat, Inc. All rights reserved.
   5  *
   6  * Module Author: Heinz Mauelshagen
   7  *
   8  * This file is released under the GPL.
   9  *
  10  * Path-Selector registration.
  11  */
  12
  13 #ifndef DM_PATH_SELECTOR_H
  14 #define DM_PATH_SELECTOR_H
  15
  16 #include <linux/device-mapper.h>
  17
  18 #include "dm-mpath.h"
  19
  20 /*
  21  * We provide an abstraction for the code that chooses which path
  22  * to send some io down.
  23  */
  24 struct path_selector_type;
  25 struct path_selector {
  26         struct path_selector_type *type;
  27         void *context;
  28 };
  29
  30 /*
  31  * If a path selector uses this flag, a high resolution timer is used
  32  * (via ktime_get_ns) to account for IO start time in BIO-based mpath.
  33  * This improves performance of some path selectors (i.e. HST), in
  34  * exchange for slightly higher overhead when submitting the BIO.
  35  * The extra cost is usually offset by improved path selection for
  36  * some benchmarks.
  37  *
  38  * This has no effect for request-based mpath, since it already uses a
  39  * higher precision timer by default.
  40  */
  41 #define DM_PS_USE_HR_TIMER              0x00000001
  42 #define dm_ps_use_hr_timer(type)        ((type)->features & DM_PS_USE_HR_TIMER)
  43
  44 /* Information about a path selector type */
  45 struct path_selector_type {
  46         char *name;
  47         struct module *module;
  48
  49         unsigned int features;
  50         unsigned int table_args;
  51         unsigned int info_args;
  52
  53         /*
  54          * Constructs a path selector object, takes custom arguments
  55          */
  56         int (*create)(struct path_selector *ps, unsigned int argc, char **argv);
  57         void (*destroy)(struct path_selector *ps);
  58
  59         /*
  60          * Add an opaque path object, along with some selector specific
  61          * path args (eg, path priority).
  62          */
  63         int (*add_path)(struct path_selector *ps, struct dm_path *path,
  64                         int argc, char **argv, char **error);
  65
  66         /*
  67          * Chooses a path for this io, if no paths are available then
  68          * NULL will be returned.
  69          */
  70         struct dm_path *(*select_path)(struct path_selector *ps, size_t nr_bytes);
  71
  72         /*
  73          * Notify the selector that a path has failed.
  74          */
  75         void (*fail_path)(struct path_selector *ps, struct dm_path *p);
  76
  77         /*
  78          * Ask selector to reinstate a path.
  79          */
  80         int (*reinstate_path)(struct path_selector *ps, struct dm_path *p);
  81
  82         /*
  83          * Table content based on parameters added in ps_add_path_fn
  84          * or path selector status
  85          */
  86         int (*status)(struct path_selector *ps, struct dm_path *path,
  87                       status_type_t type, char *result, unsigned int maxlen);
  88
  89         int (*start_io)(struct path_selector *ps, struct dm_path *path,
  90                         size_t nr_bytes);
  91         int (*end_io)(struct path_selector *ps, struct dm_path *path,
  92                       size_t nr_bytes, u64 start_time);
  93 };
  94
  95 /* Register a path selector */
  96 int dm_register_path_selector(struct path_selector_type *type);
  97
  98 /* Unregister a path selector */
  99 int dm_unregister_path_selector(struct path_selector_type *type);
 100
 101 /* Returns a registered path selector type */
 102 struct path_selector_type *dm_get_path_selector(const char *name);
 103
 104 /* Releases a path selector  */
 105 void dm_put_path_selector(struct path_selector_type *pst);
 106
 107 #endif