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44 .Nd Static sysctl declaration functions
155 kernel interfaces allow code to statically declare
157 MIB entries, which will be initialized when the kernel module containing the
158 declaration is initialized.
159 When the module is unloaded, the sysctl will be automatically destroyed.
161 Sysctl nodes are created in a hierarchical tree, with all static nodes being
162 represented by named C data structures; in order to create a new node under
163 an existing node in the tree, the structure representing the desired parent
164 node must be declared in the current context using
167 New nodes are declared using one of
180 Each macro accepts a parent name, as declared using
182 an OID number, typically
184 a node name, a set of control and access flags, and a description.
185 Depending on the macro, a pointer to a variable supporting the MIB entry, a
186 size, a value, and a function pointer implementing the MIB entry may also be
189 For most of the above macros, declaring a type as part of the access flags is
190 not necessary -- however, when declaring a sysctl implemented by a function,
191 including a type in the access mask is required:
192 .Bl -tag -width CTLTYPE_STRING
194 This is a node intended to be a parent for other nodes.
196 This is a signed integer.
197 .It Dv CTLTYPE_STRING
198 This is a nul-terminated string stored in a character array.
200 This is a 64-bit signed integer.
201 .It Dv CTLTYPE_OPAQUE
202 This is an opaque data structure.
203 .It Dv CTLTYPE_STRUCT
207 This is an unsigned integer.
209 This is a signed long.
211 This is an unsigned long.
214 All sysctl types except for new node declarations require one or more flags
215 to be set indicating the read and write disposition of the sysctl:
216 .Bl -tag -width CTLFLAG_ANYBODY
218 This is a read-only sysctl.
220 This is a writable sysctl.
222 This sysctl is readable and writable.
223 .It Dv CTLFLAG_ANYBODY
224 Any user or process can write to this sysctl.
225 .It Dv CTLFLAG_SECURE
226 This sysctl can be written to only if the effective securelevel of the
228 .It Dv CTLFLAG_PRISON
229 This sysctl can be written to by processes in
232 When iterating the sysctl name space, do not list this sysctl.
234 Also declare a system tunable with the same name to initialize this variable.
236 Also declare a system tunable with the same name to initalize this variable;
237 however, the run-time variable is read-only.
240 When creating new sysctls, careful attention should be paid to the security
241 implications of the monitoring or management interface being created.
242 Most sysctls present in the kernel are read-only or writable only by the
244 Sysctls exporting extensive information on system data structures and
245 operation, especially those implemented using procedures, will wish to
246 implement access control to limit the undesired exposure of information about
247 other processes, network connections, etc.
249 The following top level sysctl name spaces are commonly used:
250 .Bl -tag -width regression
252 Compatibility layer information.
254 Debugging information.
255 Various name spaces exist under
258 Hardware and device driver information.
260 Kernel behavior tuning; generally deprecated in favor of more specific
263 Machine-dependent configuration parameters.
266 Various protocols have name spaces under
269 Regression test configuration and information.
271 Security and security-policy configuration and information.
273 Reserved name space for the implementation of sysctl.
275 Configuration settings relating to user application behavior.
276 Generally, configuring applications using kernel sysctls is discouraged.
278 Virtual file system configuration and information.
280 Virtual memory subsystem configuration and information.
285 to declare the "security" sysctl tree for use by new nodes:
286 .Bd -literal -offset indent
287 SYSCTL_DECL(_security);
290 Examples of integer, opaque, string, and procedure sysctls follow:
291 .Bd -literal -offset indent
293 * Example of a constant integer value. Notice that the control
294 * flags are CTLFLAG_RD, the variable pointer is NULL, and the
296 * If sysctl(8) should print this value in hex, use 'SYSCTL_XINT'.
298 SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, NULL,
299 sizeof(struct bio), "sizeof(struct bio)");
302 * Example of a variable integer value. Notice that the control
303 * flags are CTLFLAG_RW, the variable pointer is set, and the
306 static int doingcache = 1; /* 1 => enable the cache */
307 SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0,
308 "Enable name cache");
311 * Example of a variable string value. Notice that the control
312 * flags are CTLFLAG_RW, that the variable pointer and string
313 * size are set. Unlike newer sysctls, this older sysctl uses a
316 char kernelname[MAXPATHLEN] = "/kernel"; /* XXX bloat */
317 SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW,
318 kernelname, sizeof(kernelname), "Name of kernel file booted");
321 * Example of an opaque data type exported by sysctl. Notice that
322 * the variable pointer and size are provided, as well as a format
323 * string for sysctl(8).
325 static l_fp pps_freq; /* scaled frequence offset (ns/s) */
326 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD,
327 &pps_freq, sizeof(pps_freq), "I", "");
330 * Example of a procedure based sysctl exporting string
331 * information. Notice that the data type is declared, the NULL
332 * variable pointer and 0 size, the function pointer, and the
333 * format string for sysctl(8).
335 SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING |
336 CTLFLAG_RW, NULL, 0, sysctl_kern_timecounter_hardware, "A",
340 When adding, modifying, or removing sysctl names, it is important to be
341 aware that these interfaces may be used by users, libraries, applications,
342 or documentation (such as published books), and are implicitly published application interfaces.
343 As with other application interfaces, caution must be taken not to break
344 existing applications, and to think about future use of new name spaces so as
345 to avoid the need to rename or remove interfaces that might be depended on in
349 .Xr sysctl_add_oid 9 ,
350 .Xr sysctl_ctx_free 9 ,
351 .Xr sysctl_ctx_init 9 ,
352 .Xr sysctl_remove_oid 9
358 The sysctl implementation originally found in
360 has been extensively rewritten by
361 .An Poul-Henning Kamp
362 in order to add support for name lookups, name space iteration, and dynamic
363 addition of MIB nodes.
365 This man page was written by
366 .An Robert N. M. Watson .