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26 .\" $FreeBSD: src/share/man/man9/sysctl.9,v 1.3 2006/04/28 23:21:36 keramida Exp $
52 .Nd Static sysctl declaration functions
235 kernel interfaces allow code to statically declare
237 MIB entries, which will be initialized when the kernel module containing the
238 declaration is initialized.
239 When the module is unloaded, the sysctl will be automatically destroyed.
241 Sysctl nodes are created in a hierarchical tree, with all static nodes being
242 represented by named C data structures; in order to create a new node under
243 an existing node in the tree, the structure representing the desired parent
244 node must be declared in the current context using
247 New nodes are declared using one of
268 Each macro accepts a parent name, as declared using
270 an OID number, typically
272 a node name, a set of control and access flags, and a description.
273 Depending on the macro, a pointer to a variable supporting the MIB entry, a
274 size, a value, and a function pointer implementing the MIB entry may also be
277 For most of the above macros, declaring a type as part of the access flags is
278 not necessary -- however, when declaring a sysctl implemented by a function,
279 including a type in the access mask is required:
280 .Bl -tag -width ".Dv CTLTYPE_STRING"
282 This is a node intended to be a parent for other nodes.
284 This is a signed integer.
286 This is an 8-bit signed integer.
288 This is a 16-bit signed integer.
290 This is a 32-bit signed integer.
292 This is a 64-bit signed integer.
293 .It Dv CTLTYPE_STRING
294 This is a nul-terminated string stored in a character array.
296 This is a 64-bit signed integer.
297 .It Dv CTLTYPE_OPAQUE
298 This is an opaque data structure.
299 .It Dv CTLTYPE_STRUCT
303 This is an 8-bit unsigned integer.
305 This is a 16-bit unsigned integer.
307 This is a 32-bit unsigned integer.
309 This is a 64-bit unsigned integer.
311 This is an unsigned integer.
313 This is a signed long.
315 This is an unsigned long.
317 This is a 64-bit unsigned integer.
320 All sysctl types except for new node declarations require one or more flags
321 to be set indicating the read and write disposition of the sysctl:
322 .Bl -tag -width ".Dv CTLFLAG_ANYBODY"
324 This is a read-only sysctl.
326 This is a writable sysctl.
328 This sysctl is readable and writable.
329 .It Dv CTLFLAG_ANYBODY
330 Any user or process can write to this sysctl.
331 .It Dv CTLFLAG_SECURE
332 This sysctl can be written to only if the effective securelevel of the
334 .It Dv CTLFLAG_PRISON
335 This sysctl can be written to by processes in
337 .\".It Dv CTLFLAG_SKIP
338 .\"When iterating the sysctl name space, do not list this sysctl.
341 When creating new sysctls, careful attention should be paid to the security
342 implications of the monitoring or management interface being created.
343 Most sysctls present in the kernel are read-only or writable only by the
345 Sysctls exporting extensive information on system data structures and
346 operation, especially those implemented using procedures, will wish to
347 implement access control to limit the undesired exposure of information about
348 other processes, network connections, etc.
350 The following top level sysctl name spaces are commonly used:
351 .Bl -tag -width ".Va machdep"
353 Compatibility layer information.
355 Debugging information.
356 Various name spaces exist under
359 Hardware and device driver information.
361 Information about the
365 Kernel behavior tuning; generally deprecated in favor of more specific
368 Machine-dependent configuration parameters.
371 Various protocols have name spaces under
374 Reserved name space for the implementation of sysctl.
376 Configuration settings relating to user application behavior.
377 Generally, configuring applications using kernel sysctls is discouraged.
379 Virtual file system configuration and information.
381 Virtual memory subsystem configuration and information.
386 to declare the "machdep" sysctl tree for use by new nodes:
387 .Bd -literal -offset indent
388 SYSCTL_DECL(_machdep);
391 Examples of integer, opaque, string, and procedure sysctls follow:
392 .Bd -literal -offset indent
394 * Example of a constant integer value. Notice that the control
395 * flags are CTLFLAG_RD, the variable pointer is NULL, and the
398 SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, NULL,
399 sizeof(struct bio), "sizeof(struct bio)");
402 * Example of a variable integer value. Notice that the control
403 * flags are CTLFLAG_RW, the variable pointer is set, and the
406 static int doingcache = 1; /* 1 => enable the cache */
407 SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0,
408 "Enable name cache");
411 * Example of a variable string value. Notice that the control
412 * flags are CTLFLAG_RW, that the variable pointer and string
413 * size are set. Unlike newer sysctls, this older sysctl uses a
416 char kernelname[MAXPATHLEN] = "/boot/kernel"; /* XXX bloat */
417 SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW,
418 kernelname, sizeof(kernelname), "Name of kernel file booted");
421 * Example of an opaque data type exported by sysctl. Notice that
422 * the variable pointer and size are provided, as well as a format
423 * string for sysctl(8).
425 static l_fp pps_freq; /* scaled frequency offset (ns/s) */
426 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD,
427 &pps_freq, sizeof(pps_freq), "I", "");
430 * Example of a procedure based sysctl exporting string
431 * information. Notice that the data type is declared, the NULL
432 * variable pointer and 0 size, the function pointer, and the
433 * format string for sysctl(8).
435 SYSCTL_PROC(_kern, OID_AUTO, msgbuf, CTLTYPE_STRING | CTLFLAG_RD,
436 0, 0, sysctl_kern_msgbuf, "A", "Contents of kernel message buffer");
439 When adding, modifying, or removing sysctl names, it is important to be
440 aware that these interfaces may be used by users, libraries, applications,
441 or documentation (such as published books), and are implicitly published
442 application interfaces.
443 As with other application interfaces, caution must be taken not to break
444 existing applications, and to think about future use of new name spaces so as
445 to avoid the need to rename or remove interfaces that might be depended on in
449 .Xr sysctl_add_oid 9 ,
450 .Xr sysctl_ctx_free 9 ,
451 .Xr sysctl_ctx_init 9 ,
452 .Xr sysctl_remove_oid 9
459 The sysctl implementation originally found in
461 has been extensively rewritten by
462 .An Poul-Henning Kamp
463 in order to add support for name lookups, name space iteration, and dynamic
464 addition of MIB nodes.
466 This man page was written by
467 .An Robert N. M. Watson .
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