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 #if !HAVE_TUNABLES
  25 static inline void
  26 __always_inline
  27 __tunables_init (char **unused __attribute__ ((unused)))
  28 {
  29   /* This is optimized out if tunables are not enabled.  */
  30 }
  31 #else
  32 # include <stdbool.h>
  33 # include <stddef.h>
  34 # include <stdint.h>
  35
  36 typedef intmax_t tunable_num_t;
  37
  38 typedef union
  39 {
  40   tunable_num_t numval;
  41   const char *strval;
  42 } tunable_val_t;
  43
  44 typedef void (*tunable_callback_t) (tunable_val_t *);
  45
  46 /* Full name for a tunable is top_ns.tunable_ns.id.  */
  47 # define TUNABLE_NAME_S(top,ns,id) #top "." #ns "." #id
  48
  49 # define TUNABLE_ENUM_NAME(__top,__ns,__id) TUNABLE_ENUM_NAME1 (__top,__ns,__id)
  50 # define TUNABLE_ENUM_NAME1(__top,__ns,__id) __top ## _ ## __ns ## _ ## __id
  51
  52 # include "dl-tunable-list.h"
  53
  54 extern void __tunables_init (char **);
  55 extern void __tunables_print (void);
  56 extern void __tunable_get_val (tunable_id_t, void *, tunable_callback_t);
  57 extern void __tunable_set_val (tunable_id_t, tunable_val_t *, tunable_num_t *,
  58                                tunable_num_t *);
  59 rtld_hidden_proto (__tunables_init)
  60 rtld_hidden_proto (__tunables_print)
  61 rtld_hidden_proto (__tunable_get_val)
  62 rtld_hidden_proto (__tunable_set_val)
  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_GET(__id, __type, __cb) \
  69   TUNABLE_GET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __cb)
  70 # define TUNABLE_SET(__id, __val) \
  71   TUNABLE_SET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __val)
  72 # define TUNABLE_SET_WITH_BOUNDS(__id, __val, __min, __max) \
  73   TUNABLE_SET_WITH_BOUNDS_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, \
  74                                 __val, __min, __max)
  75 #else
  76 # define TUNABLE_GET(__top, __ns, __id, __type, __cb) \
  77   TUNABLE_GET_FULL (__top, __ns, __id, __type, __cb)
  78 # define TUNABLE_SET(__top, __ns, __id, __val) \
  79   TUNABLE_SET_FULL (__top, __ns, __id, __val)
  80 # define TUNABLE_SET_WITH_BOUNDS(__top, __ns, __id, __val, __min, __max) \
  81   TUNABLE_SET_WITH_BOUNDS_FULL (__top, __ns, __id, __val, __min, __max)
  82 #endif
  83
  84 /* Get and return a tunable value.  If the tunable was set externally and __CB
  85    is defined then call __CB before returning the value.  */
  86 # define TUNABLE_GET_FULL(__top, __ns, __id, __type, __cb) \
  87 ({                                                                            \
  88   tunable_id_t id = TUNABLE_ENUM_NAME (__top, __ns, __id);                    \
  89   __type ret;                                                                 \
  90   __tunable_get_val (id, &ret, __cb);                                         \
  91   ret;                                                                        \
  92 })
  93
  94 /* Set a tunable value.  */
  95 # define TUNABLE_SET_FULL(__top, __ns, __id, __val) \
  96 ({                                                                            \
  97   __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id),                   \
  98                      & (tunable_val_t) {.numval = __val}, NULL, NULL);        \
  99 })
 100
 101 /* Set a tunable value together with min/max values.  */
 102 # define TUNABLE_SET_WITH_BOUNDS_FULL(__top, __ns, __id,__val, __min, __max)  \
 103 ({                                                                            \
 104   __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id),                   \
 105                      & (tunable_val_t) {.numval = __val},                     \
 106                      & (tunable_num_t) {__min},                               \
 107                      & (tunable_num_t) {__max});                              \
 108 })
 109
 110 /* Namespace sanity for callback functions.  Use this macro to keep the
 111    namespace of the modules clean.  */
 112 # define TUNABLE_CALLBACK(__name) _dl_tunable_ ## __name
 113
 114 # define TUNABLES_FRONTEND_valstring 1
 115 /* The default value for TUNABLES_FRONTEND.  */
 116 # define TUNABLES_FRONTEND_yes TUNABLES_FRONTEND_valstring
 117
 118 static __always_inline bool
 119 tunable_val_lt (tunable_num_t lhs, tunable_num_t rhs, bool unsigned_cmp)
 120 {
 121   if (unsigned_cmp)
 122     return (uintmax_t) lhs < (uintmax_t) rhs;
 123   else
 124     return lhs < rhs;
 125 }
 126
 127 static __always_inline bool
 128 tunable_val_gt (tunable_num_t lhs, tunable_num_t rhs, bool unsigned_cmp)
 129 {
 130   if (unsigned_cmp)
 131     return (uintmax_t) lhs > (uintmax_t) rhs;
 132   else
 133     return lhs > rhs;
 134 }
 135
 136 /* Compare two name strings, bounded by the name hardcoded in glibc.  */
 137 static __always_inline bool
 138 tunable_is_name (const char *orig, const char *envname)
 139 {
 140   for (;*orig != '\0' && *envname != '\0'; envname++, orig++)
 141     if (*orig != *envname)
 142       break;
 143
 144   /* The ENVNAME is immediately followed by a value.  */
 145   if (*orig == '\0' && *envname == '=')
 146     return true;
 147   else
 148     return false;
 149 }
 150
 151 #endif
 152 #endif