1 /* 2 * Copyright (C) 2003 Sistina Software. 3 * Copyright (C) 2004 Red Hat, Inc. All rights reserved. 4 * 5 * Module Author: Heinz Mauelshagen 6 * 7 * This file is released under the GPL. 8 * 9 * Path-Selector registration. 10 */ 11 12 #ifndef DM_PATH_SELECTOR_H 13 #define DM_PATH_SELECTOR_H 14 15 #include <linux/device-mapper.h> 16 17 #include "dm-mpath.h" 18 19 /* 20 * We provide an abstraction for the code that chooses which path 21 * to send some io down. 22 */ 23 struct path_selector_type; 24 struct path_selector { 25 struct path_selector_type *type; 26 void *context; 27 }; 28 29 /* 30 * If a path selector uses this flag, a high resolution timer is used 31 * (via ktime_get_ns) to account for IO start time in BIO-based mpath. 32 * This improves performance of some path selectors (i.e. HST), in 33 * exchange for slightly higher overhead when submitting the BIO. 34 * The extra cost is usually offset by improved path selection for 35 * some benchmarks. 36 * 37 * This has no effect for request-based mpath, since it already uses a 38 * higher precision timer by default. 39 */ 40 #define DM_PS_USE_HR_TIMER 0x00000001 41 #define dm_ps_use_hr_timer(type) ((type)->features & DM_PS_USE_HR_TIMER) 42 43 /* Information about a path selector type */ 44 struct path_selector_type { 45 char *name; 46 struct module *module; 47 48 unsigned int features; 49 unsigned int table_args; 50 unsigned int info_args; 51 52 /* 53 * Constructs a path selector object, takes custom arguments 54 */ 55 int (*create) (struct path_selector *ps, unsigned argc, char **argv); 56 void (*destroy) (struct path_selector *ps); 57 58 /* 59 * Add an opaque path object, along with some selector specific 60 * path args (eg, path priority). 61 */ 62 int (*add_path) (struct path_selector *ps, struct dm_path *path, 63 int argc, char **argv, char **error); 64 65 /* 66 * Chooses a path for this io, if no paths are available then 67 * NULL will be returned. 68 */ 69 struct dm_path *(*select_path) (struct path_selector *ps, 70 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