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) 2016-2021 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 union
  37 {
  38   int64_t numval;
  39   const char *strval;
  40 } tunable_val_t;
  41
  42 typedef void (*tunable_callback_t) (tunable_val_t *);
  43
  44 /* Full name for a tunable is top_ns.tunable_ns.id.  */
  45 # define TUNABLE_NAME_S(top,ns,id) #top "." #ns "." #id
  46
  47 # define TUNABLE_ENUM_NAME(__top,__ns,__id) TUNABLE_ENUM_NAME1 (__top,__ns,__id)
  48 # define TUNABLE_ENUM_NAME1(__top,__ns,__id) __top ## _ ## __ns ## _ ## __id
  49
  50 # include "dl-tunable-list.h"
  51
  52 extern void __tunables_init (char **);
  53 extern void __tunables_print (void);
  54 extern void __tunable_get_val (tunable_id_t, void *, tunable_callback_t);
  55 extern void __tunable_set_val (tunable_id_t, void *, void *, void *);
  56 rtld_hidden_proto (__tunables_init)
  57 rtld_hidden_proto (__tunables_print)
  58 rtld_hidden_proto (__tunable_get_val)
  59 rtld_hidden_proto (__tunable_set_val)
  60
  61 /* Define TUNABLE_GET and TUNABLE_SET in short form if TOP_NAMESPACE and
  62    TUNABLE_NAMESPACE are defined.  This is useful shorthand to get and set
  63    tunables within a module.  */
  64 #if defined TOP_NAMESPACE && defined TUNABLE_NAMESPACE
  65 # define TUNABLE_GET(__id, __type, __cb) \
  66   TUNABLE_GET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __cb)
  67 # define TUNABLE_SET(__id, __type, __val) \
  68   TUNABLE_SET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __val)
  69 # define TUNABLE_SET_WITH_BOUNDS(__id, __type, __val, __min, __max) \
  70   TUNABLE_SET_WITH_BOUNDS_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, \
  71                                 __type, __val, __min, __max)
  72 #else
  73 # define TUNABLE_GET(__top, __ns, __id, __type, __cb) \
  74   TUNABLE_GET_FULL (__top, __ns, __id, __type, __cb)
  75 # define TUNABLE_SET(__top, __ns, __id, __type, __val) \
  76   TUNABLE_SET_FULL (__top, __ns, __id, __type, __val)
  77 # define TUNABLE_SET_WITH_BOUNDS(__top, __ns, __id, __type, __val, \
  78                                  __min, __max) \
  79   TUNABLE_SET_WITH_BOUNDS_FULL (__top, __ns, __id, __type, __val, \
  80                                 __min, __max)
  81 #endif
  82
  83 /* Get and return a tunable value.  If the tunable was set externally and __CB
  84    is defined then call __CB before returning the value.  */
  85 # define TUNABLE_GET_FULL(__top, __ns, __id, __type, __cb) \
  86 ({                                                                            \
  87   tunable_id_t id = TUNABLE_ENUM_NAME (__top, __ns, __id);                    \
  88   __type ret;                                                                 \
  89   __tunable_get_val (id, &ret, __cb);                                         \
  90   ret;                                                                        \
  91 })
  92
  93 /* Set a tunable value.  */
  94 # define TUNABLE_SET_FULL(__top, __ns, __id, __type, __val) \
  95 ({                                                                            \
  96   __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id),                   \
  97                      & (__type) {__val}, NULL, NULL);                         \
  98 })
  99
 100 /* Set a tunable value together with min/max values.  */
 101 # define TUNABLE_SET_WITH_BOUNDS_FULL(__top, __ns, __id, __type, __val,       \
 102                                       __min, __max)                           \
 103 ({                                                                            \
 104   __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id),                   \
 105                      & (__type) {__val},  & (__type) {__min},                 \
 106                      & (__type) {__max});                                     \
 107 })
 108
 109 /* Namespace sanity for callback functions.  Use this macro to keep the
 110    namespace of the modules clean.  */
 111 # define TUNABLE_CALLBACK(__name) _dl_tunable_ ## __name
 112
 113 # define TUNABLES_FRONTEND_valstring 1
 114 /* The default value for TUNABLES_FRONTEND.  */
 115 # define TUNABLES_FRONTEND_yes TUNABLES_FRONTEND_valstring
 116
 117 /* Compare two name strings, bounded by the name hardcoded in glibc.  */
 118 static __always_inline bool
 119 tunable_is_name (const char *orig, const char *envname)
 120 {
 121   for (;*orig != '\0' && *envname != '\0'; envname++, orig++)
 122     if (*orig != *envname)
 123       break;
 124
 125   /* The ENVNAME is immediately followed by a value.  */
 126   if (*orig == '\0' && *envname == '=')
 127     return true;
 128   else
 129     return false;
 130 }
 131
 132 #endif
 133 #endif