1 /* The tunable framework. See the README to know how to use the tunable in
2 a glibc module.
3
4 Copyright (C) 2016-2023 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 #include <stddef.h>
26 #include <stdint.h>
27
28 typedef intmax_t tunable_num_t;
29
30 typedef union
31 {
32 tunable_num_t numval;
33 const char *strval;
34 } tunable_val_t;
35
36 typedef void (*tunable_callback_t) (tunable_val_t *);
37
38 /* Full name for a tunable is top_ns.tunable_ns.id. */
39 #define TUNABLE_NAME_S(top,ns,id) #top "." #ns "." #id
40
41 #define TUNABLE_ENUM_NAME(__top,__ns,__id) TUNABLE_ENUM_NAME1 (__top,__ns,__id)
42 #define TUNABLE_ENUM_NAME1(__top,__ns,__id) __top ## _ ## __ns ## _ ## __id
43
44 #include "dl-tunable-list.h"
45
46 extern void __tunables_init (char **);
47 extern void __tunables_print (void);
48 extern void __tunable_get_val (tunable_id_t, void *, tunable_callback_t);
49 extern void __tunable_set_val (tunable_id_t, tunable_val_t *, tunable_num_t *,
50 tunable_num_t *);
51 rtld_hidden_proto (__tunables_init)
52 rtld_hidden_proto (__tunables_print)
53 rtld_hidden_proto (__tunable_get_val)
54 rtld_hidden_proto (__tunable_set_val)
55
56 /* Define TUNABLE_GET and TUNABLE_SET in short form if TOP_NAMESPACE and
57 TUNABLE_NAMESPACE are defined. This is useful shorthand to get and set
58 tunables within a module. */
59 #if defined TOP_NAMESPACE && defined TUNABLE_NAMESPACE
60 # define TUNABLE_GET(__id, __type, __cb) \
61 TUNABLE_GET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __cb)
62 # define TUNABLE_SET(__id, __val) \
63 TUNABLE_SET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __val)
64 # define TUNABLE_SET_WITH_BOUNDS(__id, __val, __min, __max) \
65 TUNABLE_SET_WITH_BOUNDS_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, \
66 __val, __min, __max)
67 #else
68 # define TUNABLE_GET(__top, __ns, __id, __type, __cb) \
69 TUNABLE_GET_FULL (__top, __ns, __id, __type, __cb)
70 # define TUNABLE_SET(__top, __ns, __id, __val) \
71 TUNABLE_SET_FULL (__top, __ns, __id, __val)
72 # define TUNABLE_SET_WITH_BOUNDS(__top, __ns, __id, __val, __min, __max) \
73 TUNABLE_SET_WITH_BOUNDS_FULL (__top, __ns, __id, __val, __min, __max)
74 #endif
75
76 /* Get and return a tunable value. If the tunable was set externally and __CB
77 is defined then call __CB before returning the value. */
78 #define TUNABLE_GET_FULL(__top, __ns, __id, __type, __cb) \
79 ({ \
80 tunable_id_t id = TUNABLE_ENUM_NAME (__top, __ns, __id); \
81 __type ret; \
82 __tunable_get_val (id, &ret, __cb); \
83 ret; \
84 })
85
86 /* Set a tunable value. */
87 #define TUNABLE_SET_FULL(__top, __ns, __id, __val) \
88 ({ \
89 __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id), \
90 & (tunable_val_t) {.numval = __val}, NULL, NULL); \
91 })
92
93 /* Set a tunable value together with min/max values. */
94 #define TUNABLE_SET_WITH_BOUNDS_FULL(__top, __ns, __id,__val, __min, __max) \
95 ({ \
96 __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id), \
97 & (tunable_val_t) {.numval = __val}, \
98 & (tunable_num_t) {__min}, \
99 & (tunable_num_t) {__max}); \
100 })
101
102 /* Namespace sanity for callback functions. Use this macro to keep the
103 namespace of the modules clean. */
104 #define TUNABLE_CALLBACK(__name) _dl_tunable_ ## __name
105
106 static __always_inline bool
107 tunable_val_lt (tunable_num_t lhs, tunable_num_t rhs, bool unsigned_cmp)
108 {
109 if (unsigned_cmp)
110 return (uintmax_t) lhs < (uintmax_t) rhs;
111 else
112 return lhs < rhs;
113 }
114
115 static __always_inline bool
116 tunable_val_gt (tunable_num_t lhs, tunable_num_t rhs, bool unsigned_cmp)
117 {
118 if (unsigned_cmp)
119 return (uintmax_t) lhs > (uintmax_t) rhs;
120 else
121 return lhs > rhs;
122 }
123
124 /* Compare two name strings, bounded by the name hardcoded in glibc. */
125 static __always_inline bool
126 tunable_is_name (const char *orig, const char *envname)
127 {
128 for (;*orig != '\0' && *envname != '\0'; envname++, orig++)
129 if (*orig != *envname)
130 break;
131
132 /* The ENVNAME is immediately followed by a value. */
133 if (*orig == '\0' && *envname == '=')
134 return true;
135 else
136 return false;
137 }
138
139 #endif