1 /* The tunable framework. See the README to know how to use the tunable in
2 a glibc module.
3
4 Copyright (C) 2016-2022 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 #if !HAVE_TUNABLES
25 static inline void
26 __always_inline
__tunables_init(char ** unused)27 __tunables_init (char **unused __attribute__ ((unused)))
28 {
29 /* This is optimized out if tunables are not enabled. */
30 }
31 #else
32 # include <stdbool.h>
33 # include <stddef.h>
34 # include <stdint.h>
35
36 typedef intmax_t tunable_num_t;
37
38 typedef union
39 {
40 tunable_num_t numval;
41 const char *strval;
42 } tunable_val_t;
43
44 typedef void (*tunable_callback_t) (tunable_val_t *);
45
46 /* Full name for a tunable is top_ns.tunable_ns.id. */
47 # define TUNABLE_NAME_S(top,ns,id) #top "." #ns "." #id
48
49 # define TUNABLE_ENUM_NAME(__top,__ns,__id) TUNABLE_ENUM_NAME1 (__top,__ns,__id)
50 # define TUNABLE_ENUM_NAME1(__top,__ns,__id) __top ## _ ## __ns ## _ ## __id
51
52 # include "dl-tunable-list.h"
53
54 extern void __tunables_init (char **);
55 extern void __tunables_print (void);
56 extern void __tunable_get_val (tunable_id_t, void *, tunable_callback_t);
57 extern void __tunable_set_val (tunable_id_t, tunable_val_t *, tunable_num_t *,
58 tunable_num_t *);
59 rtld_hidden_proto (__tunables_init)
rtld_hidden_proto(__tunables_print)60 rtld_hidden_proto (__tunables_print)
61 rtld_hidden_proto (__tunable_get_val)
62 rtld_hidden_proto (__tunable_set_val)
63
64 /* Define TUNABLE_GET and TUNABLE_SET in short form if TOP_NAMESPACE and
65 TUNABLE_NAMESPACE are defined. This is useful shorthand to get and set
66 tunables within a module. */
67 #if defined TOP_NAMESPACE && defined TUNABLE_NAMESPACE
68 # define TUNABLE_GET(__id, __type, __cb) \
69 TUNABLE_GET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __cb)
70 # define TUNABLE_SET(__id, __val) \
71 TUNABLE_SET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __val)
72 # define TUNABLE_SET_WITH_BOUNDS(__id, __val, __min, __max) \
73 TUNABLE_SET_WITH_BOUNDS_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, \
74 __val, __min, __max)
75 #else
76 # define TUNABLE_GET(__top, __ns, __id, __type, __cb) \
77 TUNABLE_GET_FULL (__top, __ns, __id, __type, __cb)
78 # define TUNABLE_SET(__top, __ns, __id, __val) \
79 TUNABLE_SET_FULL (__top, __ns, __id, __val)
80 # define TUNABLE_SET_WITH_BOUNDS(__top, __ns, __id, __val, __min, __max) \
81 TUNABLE_SET_WITH_BOUNDS_FULL (__top, __ns, __id, __val, __min, __max)
82 #endif
83
84 /* Get and return a tunable value. If the tunable was set externally and __CB
85 is defined then call __CB before returning the value. */
86 # define TUNABLE_GET_FULL(__top, __ns, __id, __type, __cb) \
87 ({ \
88 tunable_id_t id = TUNABLE_ENUM_NAME (__top, __ns, __id); \
89 __type ret; \
90 __tunable_get_val (id, &ret, __cb); \
91 ret; \
92 })
93
94 /* Set a tunable value. */
95 # define TUNABLE_SET_FULL(__top, __ns, __id, __val) \
96 ({ \
97 __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id), \
98 & (tunable_val_t) {.numval = __val}, NULL, NULL); \
99 })
100
101 /* Set a tunable value together with min/max values. */
102 # define TUNABLE_SET_WITH_BOUNDS_FULL(__top, __ns, __id,__val, __min, __max) \
103 ({ \
104 __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id), \
105 & (tunable_val_t) {.numval = __val}, \
106 & (tunable_num_t) {__min}, \
107 & (tunable_num_t) {__max}); \
108 })
109
110 /* Namespace sanity for callback functions. Use this macro to keep the
111 namespace of the modules clean. */
112 # define TUNABLE_CALLBACK(__name) _dl_tunable_ ## __name
113
114 # define TUNABLES_FRONTEND_valstring 1
115 /* The default value for TUNABLES_FRONTEND. */
116 # define TUNABLES_FRONTEND_yes TUNABLES_FRONTEND_valstring
117
118 static __always_inline bool
119 tunable_val_lt (tunable_num_t lhs, tunable_num_t rhs, bool unsigned_cmp)
120 {
121 if (unsigned_cmp)
122 return (uintmax_t) lhs < (uintmax_t) rhs;
123 else
124 return lhs < rhs;
125 }
126
127 static __always_inline bool
tunable_val_gt(tunable_num_t lhs,tunable_num_t rhs,bool unsigned_cmp)128 tunable_val_gt (tunable_num_t lhs, tunable_num_t rhs, bool unsigned_cmp)
129 {
130 if (unsigned_cmp)
131 return (uintmax_t) lhs > (uintmax_t) rhs;
132 else
133 return lhs > rhs;
134 }
135
136 /* Compare two name strings, bounded by the name hardcoded in glibc. */
137 static __always_inline bool
tunable_is_name(const char * orig,const char * envname)138 tunable_is_name (const char *orig, const char *envname)
139 {
140 for (;*orig != '\0' && *envname != '\0'; envname++, orig++)
141 if (*orig != *envname)
142 break;
143
144 /* The ENVNAME is immediately followed by a value. */
145 if (*orig == '\0' && *envname == '=')
146 return true;
147 else
148 return false;
149 }
150
151 #endif
152 #endif
153