elf/dl-tunables.h

   1 /* The tunable framework.  See the README to know how to use the tunable in
   2    a glibc module.
   3
   4    Copyright (C) 2016-2023 Free Software Foundation, Inc.
   5    This file is part of the GNU C Library.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Lesser General Public
   9    License as published by the Free Software Foundation; either
  10    version 2.1 of the License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public
  18    License along with the GNU C Library; if not, see
  19    <https://www.gnu.org/licenses/>.  */
  20
  21 #ifndef _TUNABLES_H_
  22 #define _TUNABLES_H_
  23
  24 #include <stdbool.h>
  25 #include <stddef.h>
  26 #include <stdint.h>
  27
  28 typedef intmax_t tunable_num_t;
  29
  30 typedef union
  31 {
  32   tunable_num_t numval;
  33   struct tunable_str_t
  34   {
  35     const char *str;
  36     size_t len;
  37   } strval;
  38 } tunable_val_t;
  39
  40 typedef void (*tunable_callback_t) (tunable_val_t *);
  41
  42 /* Full name for a tunable is top_ns.tunable_ns.id.  */
  43 #define TUNABLE_NAME_S(top,ns,id) #top "." #ns "." #id
  44
  45 #define TUNABLE_ENUM_NAME(__top,__ns,__id) TUNABLE_ENUM_NAME1 (__top,__ns,__id)
  46 #define TUNABLE_ENUM_NAME1(__top,__ns,__id) __top ## _ ## __ns ## _ ## __id
  47
  48 #include "dl-tunable-list.h"
  49
  50 extern void __tunables_init (char **);
  51 extern void __tunables_print (void);
  52 extern bool __tunable_is_initialized (tunable_id_t);
  53 extern void __tunable_get_val (tunable_id_t, void *, tunable_callback_t);
  54 extern void __tunable_set_val (tunable_id_t, tunable_val_t *, tunable_num_t *,
  55                                tunable_num_t *);
  56 extern void __tunable_get_default (tunable_id_t id, void *valp);
  57 rtld_hidden_proto (__tunables_init)
  58 rtld_hidden_proto (__tunables_print)
  59 rtld_hidden_proto (__tunable_is_initialized)
  60 rtld_hidden_proto (__tunable_get_val)
  61 rtld_hidden_proto (__tunable_set_val)
  62 rtld_hidden_proto (__tunable_get_default)
  63
  64 /* Define TUNABLE_GET and TUNABLE_SET in short form if TOP_NAMESPACE and
  65    TUNABLE_NAMESPACE are defined.  This is useful shorthand to get and set
  66    tunables within a module.  */
  67 #if defined TOP_NAMESPACE && defined TUNABLE_NAMESPACE
  68 # define TUNABLE_IS_INITIALIZED(__id) \
  69   TUNABLE_IS_INITIALIZED_FULL(TOP_NAMESPACE, TUNABLE_NAMESPACE, __id)
  70 # define TUNABLE_GET_DEFAULT(__id, __type) \
  71   TUNABLE_GET_DEFAULT_FULL(TOP_NAMESPACE, TUNABLE_NAMESPACE,__id, __type)
  72 # define TUNABLE_GET(__id, __type, __cb) \
  73   TUNABLE_GET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __cb)
  74 # define TUNABLE_SET(__id, __val) \
  75   TUNABLE_SET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __val)
  76 # define TUNABLE_SET_WITH_BOUNDS(__id, __val, __min, __max) \
  77   TUNABLE_SET_WITH_BOUNDS_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, \
  78                                 __val, __min, __max)
  79 #else
  80 # define TUNABLE_IS_INITIALIZED(__top, __ns, __id) \
  81   TUNABLE_IS_INITIALIZED_FULL(__top, __ns, __id)
  82 # define TUNABLE_GET_DEFAULT(__top, __ns, __type) \
  83   TUNABLE_GET_DEFAULT_FULL(__top, __ns, __id, __type)
  84 # define TUNABLE_GET(__top, __ns, __id, __type, __cb) \
  85   TUNABLE_GET_FULL (__top, __ns, __id, __type, __cb)
  86 # define TUNABLE_SET(__top, __ns, __id, __val) \
  87   TUNABLE_SET_FULL (__top, __ns, __id, __val)
  88 # define TUNABLE_SET_WITH_BOUNDS(__top, __ns, __id, __val, __min, __max) \
  89   TUNABLE_SET_WITH_BOUNDS_FULL (__top, __ns, __id, __val, __min, __max)
  90 #endif
  91
  92 /* Return whether the tunable was initialized by the environment variable.  */
  93 #define TUNABLE_IS_INITIALIZED_FULL(__top, __ns, __id) \
  94 ({                                                                            \
  95   tunable_id_t id = TUNABLE_ENUM_NAME (__top, __ns, __id);                    \
  96   __tunable_is_initialized (id);                                              \
  97 })
  98
  99 /* Return the default value of the tunable.  */
 100 #define TUNABLE_GET_DEFAULT_FULL(__top, __ns, __id, __type) \
 101 ({                                                                            \
 102   tunable_id_t id = TUNABLE_ENUM_NAME (__top, __ns, __id);                    \
 103   __type __ret;                                                               \
 104   __tunable_get_default (id, &__ret);                                         \
 105   __ret;                                                                      \
 106 })
 107
 108 /* Get and return a tunable value.  If the tunable was set externally and __CB
 109    is defined then call __CB before returning the value.  */
 110 #define TUNABLE_GET_FULL(__top, __ns, __id, __type, __cb) \
 111 ({                                                                            \
 112   tunable_id_t id = TUNABLE_ENUM_NAME (__top, __ns, __id);                    \
 113   __type ret;                                                                 \
 114   __tunable_get_val (id, &ret, __cb);                                         \
 115   ret;                                                                        \
 116 })
 117
 118 /* Set a tunable value.  */
 119 #define TUNABLE_SET_FULL(__top, __ns, __id, __val) \
 120 ({                                                                            \
 121   __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id),                   \
 122                      & (tunable_val_t) {.numval = __val}, NULL, NULL);        \
 123 })
 124
 125 /* Set a tunable value together with min/max values.  */
 126 #define TUNABLE_SET_WITH_BOUNDS_FULL(__top, __ns, __id,__val, __min, __max)  \
 127 ({                                                                            \
 128   __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id),                   \
 129                      & (tunable_val_t) {.numval = __val},                     \
 130                      & (tunable_num_t) {__min},                               \
 131                      & (tunable_num_t) {__max});                              \
 132 })
 133
 134 /* Namespace sanity for callback functions.  Use this macro to keep the
 135    namespace of the modules clean.  */
 136 #define TUNABLE_CALLBACK(__name) _dl_tunable_ ## __name
 137
 138 static __always_inline bool
 139 tunable_val_lt (tunable_num_t lhs, tunable_num_t rhs, bool unsigned_cmp)
 140 {
 141   if (unsigned_cmp)
 142     return (uintmax_t) lhs < (uintmax_t) rhs;
 143   else
 144     return lhs < rhs;
 145 }
 146
 147 static __always_inline bool
 148 tunable_val_gt (tunable_num_t lhs, tunable_num_t rhs, bool unsigned_cmp)
 149 {
 150   if (unsigned_cmp)
 151     return (uintmax_t) lhs > (uintmax_t) rhs;
 152   else
 153     return lhs > rhs;
 154 }
 155
 156 /* Compare two name strings, bounded by the name hardcoded in glibc.  */
 157 static __always_inline bool
 158 tunable_is_name (const char *orig, const char *envname)
 159 {
 160   for (;*orig != '\0' && *envname != '\0'; envname++, orig++)
 161     if (*orig != *envname)
 162       break;
 163
 164   /* The ENVNAME is immediately followed by a value.  */
 165   if (*orig == '\0' && *envname == '=')
 166     return true;
 167   else
 168     return false;
 169 }
 170
 171 #endif