glibc/elf/dl-tunables.h

/* The tunable framework.  See the README to know how to use the tunable in
   a glibc module.

   Copyright (C) 2016-2024 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#ifndef _TUNABLES_H_
#define _TUNABLES_H_

#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>

typedef intmax_t tunable_num_t;

typedef union
{
  tunable_num_t numval;
  struct tunable_str_t
  {
    const char *str;
    size_t len;
  } strval;
} tunable_val_t;

typedef void (*tunable_callback_t) (tunable_val_t *);

/* Full name for a tunable is top_ns.tunable_ns.id.  */
#define TUNABLE_NAME_S(top,ns,id) #top "." #ns "." #id

#define TUNABLE_ENUM_NAME(__top,__ns,__id) TUNABLE_ENUM_NAME1 (__top,__ns,__id)
#define TUNABLE_ENUM_NAME1(__top,__ns,__id) __top ## _ ## __ns ## _ ## __id

#include "dl-tunable-list.h"

extern void __tunables_init (char **);
extern void __tunables_print (void);
extern bool __tunable_is_initialized (tunable_id_t);
extern void __tunable_get_val (tunable_id_t, void *, tunable_callback_t);
extern void __tunable_set_val (tunable_id_t, tunable_val_t *, tunable_num_t *,
			       tunable_num_t *);
extern void __tunable_get_default (tunable_id_t id, void *valp);
rtld_hidden_proto (__tunables_init)
rtld_hidden_proto (__tunables_print)
rtld_hidden_proto (__tunable_is_initialized)
rtld_hidden_proto (__tunable_get_val)
rtld_hidden_proto (__tunable_set_val)
rtld_hidden_proto (__tunable_get_default)

/* Define TUNABLE_GET and TUNABLE_SET in short form if TOP_NAMESPACE and
   TUNABLE_NAMESPACE are defined.  This is useful shorthand to get and set
   tunables within a module.  */
#if defined TOP_NAMESPACE && defined TUNABLE_NAMESPACE
# define TUNABLE_IS_INITIALIZED(__id) \
  TUNABLE_IS_INITIALIZED_FULL(TOP_NAMESPACE, TUNABLE_NAMESPACE, __id)
# define TUNABLE_GET_DEFAULT(__id, __type) \
  TUNABLE_GET_DEFAULT_FULL(TOP_NAMESPACE, TUNABLE_NAMESPACE,__id, __type)
# define TUNABLE_GET(__id, __type, __cb) \
  TUNABLE_GET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __cb)
# define TUNABLE_SET(__id, __val) \
  TUNABLE_SET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __val)
# define TUNABLE_SET_WITH_BOUNDS(__id, __val, __min, __max) \
  TUNABLE_SET_WITH_BOUNDS_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, \
				__val, __min, __max)
#else
# define TUNABLE_IS_INITIALIZED(__top, __ns, __id) \
  TUNABLE_IS_INITIALIZED_FULL(__top, __ns, __id)
# define TUNABLE_GET_DEFAULT(__top, __ns, __type) \
  TUNABLE_GET_DEFAULT_FULL(__top, __ns, __id, __type)
# define TUNABLE_GET(__top, __ns, __id, __type, __cb) \
  TUNABLE_GET_FULL (__top, __ns, __id, __type, __cb)
# define TUNABLE_SET(__top, __ns, __id, __val) \
  TUNABLE_SET_FULL (__top, __ns, __id, __val)
# define TUNABLE_SET_WITH_BOUNDS(__top, __ns, __id, __val, __min, __max) \
  TUNABLE_SET_WITH_BOUNDS_FULL (__top, __ns, __id, __val, __min, __max)
#endif

/* Return whether the tunable was initialized by the environment variable.  */
#define TUNABLE_IS_INITIALIZED_FULL(__top, __ns, __id) \
({									      \
  tunable_id_t id = TUNABLE_ENUM_NAME (__top, __ns, __id);		      \
  __tunable_is_initialized (id);					      \
})

/* Return the default value of the tunable.  */
#define TUNABLE_GET_DEFAULT_FULL(__top, __ns, __id, __type) \
({									      \
  tunable_id_t id = TUNABLE_ENUM_NAME (__top, __ns, __id);		      \
  __type __ret;								      \
  __tunable_get_default (id, &__ret);					      \
  __ret;								      \
})

/* Get and return a tunable value.  If the tunable was set externally and __CB
   is defined then call __CB before returning the value.  */
#define TUNABLE_GET_FULL(__top, __ns, __id, __type, __cb) \
({									      \
  tunable_id_t id = TUNABLE_ENUM_NAME (__top, __ns, __id);		      \
  __type ret;								      \
  __tunable_get_val (id, &ret, __cb);					      \
  ret;									      \
})

/* Set a tunable value.  */
#define TUNABLE_SET_FULL(__top, __ns, __id, __val) \
({									      \
  __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id),		      \
		     & (tunable_val_t) {.numval = __val}, NULL, NULL);	      \
})

/* Set a tunable value together with min/max values.  */
#define TUNABLE_SET_WITH_BOUNDS_FULL(__top, __ns, __id,__val, __min, __max)  \
({									      \
  __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id),		      \
		     & (tunable_val_t) {.numval = __val},		      \
		     & (tunable_num_t) {__min},				      \
		     & (tunable_num_t) {__max});			      \
})

/* Namespace sanity for callback functions.  Use this macro to keep the
   namespace of the modules clean.  */
#define TUNABLE_CALLBACK(__name) _dl_tunable_ ## __name

static __always_inline bool
tunable_val_lt (tunable_num_t lhs, tunable_num_t rhs, bool unsigned_cmp)
{
  if (unsigned_cmp)
    return (uintmax_t) lhs < (uintmax_t) rhs;
  else
    return lhs < rhs;
}

static __always_inline bool
tunable_val_gt (tunable_num_t lhs, tunable_num_t rhs, bool unsigned_cmp)
{
  if (unsigned_cmp)
    return (uintmax_t) lhs > (uintmax_t) rhs;
  else
    return lhs > rhs;
}

/* Compare two name strings, bounded by the name hardcoded in glibc.  */
static __always_inline bool
tunable_is_name (const char *orig, const char *envname)
{
  for (;*orig != '\0' && *envname != '\0'; envname++, orig++)
    if (*orig != *envname)
      break;

  /* The ENVNAME is immediately followed by a value.  */
  if (*orig == '\0' && *envname == '=')
    return true;
  else
    return false;
}

#endif