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) 2016-2017 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    <http://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
  33 # include <stddef.h>
  34 # include "dl-tunable-types.h"
  35
  36 /* A tunable.  */
  37 struct _tunable
  38 {
  39   const char *name;                     /* Internal name of the tunable.  */
  40   tunable_type_t type;                  /* Data type of the tunable.  */
  41   tunable_val_t val;                    /* The value.  */
  42   const char *strval;                   /* The string containing the value,
  43                                            points into envp.  */
  44   bool is_secure;                       /* Whether the tunable must be read
  45                                            even for setuid binaries.  Note that
  46                                            even if the tunable is read, it may
  47                                            not get used by the target module if
  48                                            the value is considered unsafe.  */
  49   /* Compatibility elements.  */
  50   const char *env_alias;                /* The compatibility environment
  51                                            variable name.  */
  52 };
  53
  54 typedef struct _tunable tunable_t;
  55
  56 /* Full name for a tunable is top_ns.tunable_ns.id.  */
  57 # define TUNABLE_NAME_S(top,ns,id) #top "." #ns "." #id
  58
  59 # define TUNABLE_ENUM_NAME(top,ns,id) TUNABLE_ENUM_NAME1 (top,ns,id)
  60 # define TUNABLE_ENUM_NAME1(top,ns,id) top ## _ ## ns ## _ ## id
  61
  62 # include "dl-tunable-list.h"
  63
  64 extern void __tunables_init (char **);
  65 extern void __tunable_set_val (tunable_id_t, void *, tunable_callback_t);
  66
  67 /* Check if the tunable has been set to a non-default value and if it is, copy
  68    it over into __VAL.  */
  69 # define TUNABLE_SET_VAL(__id,__val) \
  70 ({                                                                            \
  71   __tunable_set_val                                                           \
  72    (TUNABLE_ENUM_NAME (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id), (__val),      \
  73     NULL);                                                                    \
  74 })
  75
  76 /* Same as TUNABLE_SET_VAL, but also call the callback function __CB.  */
  77 # define TUNABLE_SET_VAL_WITH_CALLBACK(__id,__val,__cb) \
  78 ({                                                                            \
  79   __tunable_set_val                                                           \
  80    (TUNABLE_ENUM_NAME (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id), (__val),      \
  81     DL_TUNABLE_CALLBACK (__cb));                                              \
  82 })
  83
  84 /* Namespace sanity for callback functions.  Use this macro to keep the
  85    namespace of the modules clean.  */
  86 # define DL_TUNABLE_CALLBACK(__name) _dl_tunable_ ## __name
  87
  88 # define TUNABLES_FRONTEND_valstring 1
  89 /* The default value for TUNABLES_FRONTEND.  */
  90 # define TUNABLES_FRONTEND_yes TUNABLES_FRONTEND_valstring
  91 #endif
  92 #endif