1/* The tunable framework. See the README to know how to use the tunable in
2 a glibc module.
3
4 Copyright (C) 2016-2020 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
26#if !HAVE_TUNABLES
27static inline void
28__always_inline
29__tunables_init (char **unused __attribute__ ((unused)))
30{
31 /* This is optimized out if tunables are not enabled. */
32}
33#else
34
35# include <stddef.h>
36# include "dl-tunable-types.h"
37
38/* A tunable. */
39struct _tunable
40{
41 const char *name; /* Internal name of the tunable. */
42 tunable_type_t type; /* Data type of the tunable. */
43 tunable_val_t val; /* The value. */
44 bool initialized; /* Flag to indicate that the tunable is
45 initialized. */
46 tunable_seclevel_t security_level; /* Specify the security level for the
47 tunable with respect to AT_SECURE
48 programs. See description of
49 tunable_seclevel_t to see a
50 description of the values.
51
52 Note that even if the tunable is
53 read, it may not get used by the
54 target module if the value is
55 considered unsafe. */
56 /* Compatibility elements. */
57 const char *env_alias; /* The compatibility environment
58 variable name. */
59};
60
61typedef struct _tunable tunable_t;
62
63/* Full name for a tunable is top_ns.tunable_ns.id. */
64# define TUNABLE_NAME_S(top,ns,id) #top "." #ns "." #id
65
66# define TUNABLE_ENUM_NAME(__top,__ns,__id) TUNABLE_ENUM_NAME1 (__top,__ns,__id)
67# define TUNABLE_ENUM_NAME1(__top,__ns,__id) __top ## _ ## __ns ## _ ## __id
68
69# include "dl-tunable-list.h"
70
71extern void __tunables_init (char **);
72extern void __tunable_get_val (tunable_id_t, void *, tunable_callback_t);
73extern void __tunable_set_val (tunable_id_t, void *);
74rtld_hidden_proto (__tunables_init)
75rtld_hidden_proto (__tunable_get_val)
76
77/* Define TUNABLE_GET and TUNABLE_SET in short form if TOP_NAMESPACE and
78 TUNABLE_NAMESPACE are defined. This is useful shorthand to get and set
79 tunables within a module. */
80#if defined TOP_NAMESPACE && defined TUNABLE_NAMESPACE
81# define TUNABLE_GET(__id, __type, __cb) \
82 TUNABLE_GET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __cb)
83# define TUNABLE_SET(__id, __type, __val) \
84 TUNABLE_SET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __val)
85#else
86# define TUNABLE_GET(__top, __ns, __id, __type, __cb) \
87 TUNABLE_GET_FULL (__top, __ns, __id, __type, __cb)
88# define TUNABLE_SET(__top, __ns, __id, __type, __val) \
89 TUNABLE_SET_FULL (__top, __ns, __id, __type, __val)
90#endif
91
92/* Get and return a tunable value. If the tunable was set externally and __CB
93 is defined then call __CB before returning the value. */
94# define TUNABLE_GET_FULL(__top, __ns, __id, __type, __cb) \
95({ \
96 tunable_id_t id = TUNABLE_ENUM_NAME (__top, __ns, __id); \
97 __type ret; \
98 __tunable_get_val (id, &ret, __cb); \
99 ret; \
100})
101
102/* Set a tunable value. */
103# define TUNABLE_SET_FULL(__top, __ns, __id, __type, __val) \
104({ \
105 __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id), \
106 & (__type) {__val}); \
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. */
118static __always_inline bool
119tunable_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
134