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   const char *strval;
  34 } tunable_val_t;
  35
  36 typedef void (*tunable_callback_t) (tunable_val_t *);
  37
  38 /* Full name for a tunable is top_ns.tunable_ns.id.  */
  39 #define TUNABLE_NAME_S(top,ns,id) #top "." #ns "." #id
  40
  41 #define TUNABLE_ENUM_NAME(__top,__ns,__id) TUNABLE_ENUM_NAME1 (__top,__ns,__id)
  42 #define TUNABLE_ENUM_NAME1(__top,__ns,__id) __top ## _ ## __ns ## _ ## __id
  43
  44 #include "dl-tunable-list.h"
  45
  46 extern void __tunables_init (char **);
  47 extern void __tunables_print (void);
  48 extern void __tunable_get_val (tunable_id_t, void *, tunable_callback_t);
  49 extern void __tunable_set_val (tunable_id_t, tunable_val_t *, tunable_num_t *,
  50                                tunable_num_t *);
  51 rtld_hidden_proto (__tunables_init)
  52 rtld_hidden_proto (__tunables_print)
  53 rtld_hidden_proto (__tunable_get_val)
  54 rtld_hidden_proto (__tunable_set_val)
  55
  56 /* Define TUNABLE_GET and TUNABLE_SET in short form if TOP_NAMESPACE and
  57    TUNABLE_NAMESPACE are defined.  This is useful shorthand to get and set
  58    tunables within a module.  */
  59 #if defined TOP_NAMESPACE && defined TUNABLE_NAMESPACE
  60 # define TUNABLE_GET(__id, __type, __cb) \
  61   TUNABLE_GET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __cb)
  62 # define TUNABLE_SET(__id, __val) \
  63   TUNABLE_SET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __val)
  64 # define TUNABLE_SET_WITH_BOUNDS(__id, __val, __min, __max) \
  65   TUNABLE_SET_WITH_BOUNDS_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, \
  66                                 __val, __min, __max)
  67 #else
  68 # define TUNABLE_GET(__top, __ns, __id, __type, __cb) \
  69   TUNABLE_GET_FULL (__top, __ns, __id, __type, __cb)
  70 # define TUNABLE_SET(__top, __ns, __id, __val) \
  71   TUNABLE_SET_FULL (__top, __ns, __id, __val)
  72 # define TUNABLE_SET_WITH_BOUNDS(__top, __ns, __id, __val, __min, __max) \
  73   TUNABLE_SET_WITH_BOUNDS_FULL (__top, __ns, __id, __val, __min, __max)
  74 #endif
  75
  76 /* Get and return a tunable value.  If the tunable was set externally and __CB
  77    is defined then call __CB before returning the value.  */
  78 #define TUNABLE_GET_FULL(__top, __ns, __id, __type, __cb) \
  79 ({                                                                            \
  80   tunable_id_t id = TUNABLE_ENUM_NAME (__top, __ns, __id);                    \
  81   __type ret;                                                                 \
  82   __tunable_get_val (id, &ret, __cb);                                         \
  83   ret;                                                                        \
  84 })
  85
  86 /* Set a tunable value.  */
  87 #define TUNABLE_SET_FULL(__top, __ns, __id, __val) \
  88 ({                                                                            \
  89   __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id),                   \
  90                      & (tunable_val_t) {.numval = __val}, NULL, NULL);        \
  91 })
  92
  93 /* Set a tunable value together with min/max values.  */
  94 #define TUNABLE_SET_WITH_BOUNDS_FULL(__top, __ns, __id,__val, __min, __max)  \
  95 ({                                                                            \
  96   __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id),                   \
  97                      & (tunable_val_t) {.numval = __val},                     \
  98                      & (tunable_num_t) {__min},                               \
  99                      & (tunable_num_t) {__max});                              \
 100 })
 101
 102 /* Namespace sanity for callback functions.  Use this macro to keep the
 103    namespace of the modules clean.  */
 104 #define TUNABLE_CALLBACK(__name) _dl_tunable_ ## __name
 105
 106 static __always_inline bool
 107 tunable_val_lt (tunable_num_t lhs, tunable_num_t rhs, bool unsigned_cmp)
 108 {
 109   if (unsigned_cmp)
 110     return (uintmax_t) lhs < (uintmax_t) rhs;
 111   else
 112     return lhs < rhs;
 113 }
 114
 115 static __always_inline bool
 116 tunable_val_gt (tunable_num_t lhs, tunable_num_t rhs, bool unsigned_cmp)
 117 {
 118   if (unsigned_cmp)
 119     return (uintmax_t) lhs > (uintmax_t) rhs;
 120   else
 121     return lhs > rhs;
 122 }
 123
 124 /* Compare two name strings, bounded by the name hardcoded in glibc.  */
 125 static __always_inline bool
 126 tunable_is_name (const char *orig, const char *envname)
 127 {
 128   for (;*orig != '\0' && *envname != '\0'; envname++, orig++)
 129     if (*orig != *envname)
 130       break;
 131
 132   /* The ENVNAME is immediately followed by a value.  */
 133   if (*orig == '\0' && *envname == '=')
 134     return true;
 135   else
 136     return false;
 137 }
 138
 139 #endif