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43 .Nd Static sysctl declaration functions
48 .Fn SYSCTL_INT parent nbr name access ptr val descr
49 .Fn SYSCTL_LONG parent nbr name access ptr val descr
50 .Fn SYSCTL_NODE parent nbr name access handler descr
51 .Fn SYSCTL_OPAQUE parent nbr name access ptr len fmt descr
52 .Fn SYSCTL_PROC parent nbr name access ptr arg handler fmt descr
53 .Fn SYSCTL_STRING parent nbr name access arg len descr
54 .Fn SYSCTL_STRUCT parent nbr name access ptr type descr
55 .Fn SYSCTL_UINT parent nbr name access ptr val descr
56 .Fn SYSCTL_ULONG parent nbr name access ptr val descr
57 .Fn SYSCTL_QUAD parent nbr name access ptr val descr
61 kernel interfaces allow code to statically declare
63 MIB entries, which will be initialized when the kernel module containing the
64 declaration is initialized.
65 When the module is unloaded, the sysctl will be automatically destroyed.
67 Sysctl nodes are created in a hierarchical tree, with all static nodes being
68 represented by named C data structures; in order to create a new node under
69 an existing node in the tree, the structure representing the desired parent
70 node must be declared in the current context using
73 New nodes are declared using one of
85 Each macro accepts a parent name, as declared using
87 an OID number, typically
89 a node name, a set of control and access flags, and a description.
90 Depending on the macro, a pointer to a variable supporting the MIB entry, a
91 size, a value, and a function pointer implementing the MIB entry may also be
94 For most of the above macros, declaring a type as part of the access flags is
95 not necessary \[em] however, when declaring a sysctl implemented by a function,
96 including a type in the access mask is required:
97 .Bl -tag -width ".Dv CTLTYPE_STRING"
99 This is a node intended to be a parent for other nodes.
101 This is a signed integer.
102 .It Dv CTLTYPE_STRING
103 This is a nul-terminated string stored in a character array.
105 This is a 64-bit signed integer.
106 .It Dv CTLTYPE_OPAQUE
107 This is an opaque data structure.
108 .It Dv CTLTYPE_STRUCT
112 This is an unsigned integer.
114 This is a signed long.
116 This is an unsigned long.
118 This is a 64-bit unsigned integer.
121 All sysctl types except for new node declarations require one or more flags
122 to be set indicating the read and write disposition of the sysctl:
123 .Bl -tag -width ".Dv CTLFLAG_ANYBODY"
125 This is a read-only sysctl.
127 This is a writable sysctl.
129 This sysctl is readable and writable.
130 .It Dv CTLFLAG_ANYBODY
131 Any user or process can write to this sysctl.
132 .It Dv CTLFLAG_SECURE
133 This sysctl can be written to only if the effective securelevel of the
135 .It Dv CTLFLAG_PRISON
136 This sysctl can be written to by processes in
139 When iterating the sysctl name space, do not list this sysctl.
141 Advisory flag that a system tunable also exists for this variable.
143 Advisory flag that a system tunable also exists for this variable;
144 however, the run-time variable is read-only.
147 When creating new sysctls, careful attention should be paid to the security
148 implications of the monitoring or management interface being created.
149 Most sysctls present in the kernel are read-only or writable only by the
151 Sysctls exporting extensive information on system data structures and
152 operation, especially those implemented using procedures, will wish to
153 implement access control to limit the undesired exposure of information about
154 other processes, network connections, etc.
156 The following top level sysctl name spaces are commonly used:
157 .Bl -tag -width ".Va regression"
159 Compatibility layer information.
161 Debugging information.
162 Various name spaces exist under
165 Hardware and device driver information.
167 Kernel behavior tuning; generally deprecated in favor of more specific
170 Machine-dependent configuration parameters.
173 Various protocols have name spaces under
176 Regression test configuration and information.
178 Security and security-policy configuration and information.
180 Reserved name space for the implementation of sysctl.
182 Configuration settings relating to user application behavior.
183 Generally, configuring applications using kernel sysctls is discouraged.
185 Virtual file system configuration and information.
187 Virtual memory subsystem configuration and information.
194 sysctl tree for use by new nodes:
195 .Bd -literal -offset indent
196 SYSCTL_DECL(_security);
199 Examples of integer, opaque, string, and procedure sysctls follow:
200 .Bd -literal -offset indent
202 * Example of a constant integer value. Notice that the control
203 * flags are CTLFLAG_RD, the variable pointer is NULL, and the
206 SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, NULL,
207 sizeof(struct bio), "sizeof(struct bio)");
210 * Example of a variable integer value. Notice that the control
211 * flags are CTLFLAG_RW, the variable pointer is set, and the
214 static int doingcache = 1; /* 1 => enable the cache */
215 SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0,
216 "Enable name cache");
219 * Example of a variable string value. Notice that the control
220 * flags are CTLFLAG_RW, that the variable pointer and string
221 * size are set. Unlike newer sysctls, this older sysctl uses a
224 char kernelname[MAXPATHLEN] = "/kernel"; /* XXX bloat */
225 SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW,
226 kernelname, sizeof(kernelname), "Name of kernel file booted");
229 * Example of an opaque data type exported by sysctl. Notice that
230 * the variable pointer and size are provided, as well as a format
231 * string for sysctl(8).
233 static l_fp pps_freq; /* scaled frequence offset (ns/s) */
234 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD,
235 &pps_freq, sizeof(pps_freq), "I", "");
238 * Example of a procedure based sysctl exporting string
239 * information. Notice that the data type is declared, the NULL
240 * variable pointer and 0 size, the function pointer, and the
241 * format string for sysctl(8).
243 SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING |
244 CTLFLAG_RW, NULL, 0, sysctl_kern_timecounter_hardware, "A",
248 When adding, modifying, or removing sysctl names, it is important to be
249 aware that these interfaces may be used by users, libraries, applications,
250 or documentation (such as published books), and are implicitly published application interfaces.
251 As with other application interfaces, caution must be taken not to break
252 existing applications, and to think about future use of new name spaces so as
253 to avoid the need to rename or remove interfaces that might be depended on in
256 The semantics chosen for a new sysctl should be as clear as possible,
257 and the name of the sysctl must closely reflect its semantics.
258 Therefore the sysctl name deserves a fair amount of consideration.
259 It should be short but yet representative of the sysctl meaning.
260 If the name consists of several words, they should be separated by
261 underscore characters, as in
262 .Va compute_summary_at_mount .
263 Underscore characters may be omitted only if the name consists of not more
264 than two words, each being not longer than four characters, as in
266 For boolean sysctls, negative logic should be totally avoided.
267 That is, do not use names like
271 They are confusing and lead to configuration errors.
272 Use positive logic instead:
276 A temporary sysctl node that should not be relied upon must be designated
277 as such by a leading underscore character in its name. For example:
282 .Xr sysctl_add_oid 9 ,
283 .Xr sysctl_ctx_free 9 ,
284 .Xr sysctl_ctx_init 9 ,
285 .Xr sysctl_remove_oid 9
289 utility first appeared in
295 implementation originally found in
297 has been extensively rewritten by
298 .An Poul-Henning Kamp
299 in order to add support for name lookups, name space iteration, and dynamic
300 addition of MIB nodes.
302 This man page was written by
303 .An Robert N. M. Watson .