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/* The tunable framework. See the README to know how to use the tunable in
a glibc module.
Copyright (C) 2016-2025 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
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