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 108