2 .\" Copyright (c) 2006 Robert N. M. Watson
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36 .Nm SYSCTL_ADD_OPAQUE ,
39 .Nm SYSCTL_ADD_ROOT_NODE ,
40 .Nm SYSCTL_ADD_STRING ,
41 .Nm SYSCTL_ADD_STRUCT ,
44 .Nm SYSCTL_ADD_UAUTO ,
46 .Nm SYSCTL_ADD_ULONG ,
47 .Nm SYSCTL_ADD_UQUAD ,
49 .Nm SYSCTL_STATIC_CHILDREN ,
50 .Nm SYSCTL_NODE_CHILDREN ,
58 .Nm SYSCTL_ROOT_NODE ,
66 .Nd Dynamic and static sysctl MIB creation functions
71 .Ft struct sysctl_oid *
73 .Fa "struct sysctl_ctx_list *ctx"
74 .Fa "struct sysctl_oid_list *parent"
76 .Fa "const char *name"
80 .Fa "const char *descr"
82 .Ft struct sysctl_oid *
84 .Fa "struct sysctl_ctx_list *ctx"
85 .Fa "struct sysctl_oid_list *parent"
87 .Fa "const char *name"
90 .Fa "const char *descr"
92 .Ft struct sysctl_oid *
94 .Fa "struct sysctl_ctx_list *ctx"
95 .Fa "struct sysctl_oid_list *parent"
97 .Fa "const char *name"
99 .Fa "int (*handler)(SYSCTL_HANDLER_ARGS)"
100 .Fa "const char *descr"
102 .Ft struct sysctl_oid *
103 .Fo SYSCTL_ADD_OPAQUE
104 .Fa "struct sysctl_ctx_list *ctx"
105 .Fa "struct sysctl_oid_list *parent"
107 .Fa "const char *name"
111 .Fa "const char *format"
112 .Fa "const char *descr"
114 .Ft struct sysctl_oid *
116 .Fa "struct sysctl_ctx_list *ctx"
117 .Fa "struct sysctl_oid_list *parent"
119 .Fa "const char *name"
123 .Fa "int (*handler) (SYSCTL_HANDLERARGS)"
124 .Fa "const char *format"
125 .Fa "const char *descr"
127 .Ft struct sysctl_oid *
129 .Fa "struct sysctl_ctx_list *ctx"
130 .Fa "struct sysctl_oid_list *parent"
132 .Fa "const char *name"
135 .Fa "const char *descr"
137 .Ft struct sysctl_oid *
138 .Fo SYSCTL_ADD_ROOT_NODE
139 .Fa "struct sysctl_ctx_list *ctx"
141 .Fa "const char *name"
143 .Fa "int (*handler)(SYSCTL_HANDLER_ARGS)"
144 .Fa "const char *descr"
146 .Ft struct sysctl_oid *
147 .Fo SYSCTL_ADD_STRING
148 .Fa "struct sysctl_ctx_list *ctx"
149 .Fa "struct sysctl_oid_list *parent"
151 .Fa "const char *name"
155 .Fa "const char *descr"
157 .Ft struct sysctl_oid *
158 .Fo SYSCTL_ADD_STRUCT
159 .Fa "struct sysctl_ctx_list *ctx"
160 .Fa "struct sysctl_oid_list *parent"
162 .Fa "const char *name"
166 .Fa "const char *descr"
168 .Ft struct sysctl_oid *
170 .Fa "struct sysctl_ctx_list *ctx"
171 .Fa "struct sysctl_oid_list *parent"
173 .Fa "const char *name"
175 .Fa "unsigned int *ptr"
177 .Fa "const char *descr"
179 .Ft struct sysctl_oid *
181 .Fa "struct sysctl_ctx_list *ctx"
182 .Fa "struct sysctl_oid_list *parent"
184 .Fa "const char *name"
186 .Fa "unsigned int *ptr"
188 .Fa "const char *descr"
190 .Ft struct sysctl_oid *
192 .Fa "struct sysctl_ctx_list *ctx"
193 .Fa "struct sysctl_oid_list *parent"
195 .Fa "const char *name"
197 .Fa "unsigned int *ptr"
199 .Fa "const char *descr"
201 .Ft struct sysctl_oid *
203 .Fa "struct sysctl_ctx_list *ctx"
204 .Fa "struct sysctl_oid_list *parent"
206 .Fa "const char *name"
208 .Fa "unsigned long *ptr"
209 .Fa "const char *descr"
211 .Ft struct sysctl_oid *
213 .Fa "struct sysctl_ctx_list *ctx"
214 .Fa "struct sysctl_oid_list *parent"
216 .Fa "const char *name"
219 .Fa "const char *descr"
221 .Ft struct sysctl_oid *
223 .Fa "struct sysctl_ctx_list *ctx"
224 .Fa "struct sysctl_oid_list *parent"
226 .Fa "const char *name"
229 .Fa "const char *descr"
231 .Ft struct sysctl_oid_list *
233 .Fa "struct sysctl_oid *oidp"
235 .Ft struct sysctl_oid_list *
236 .Fo SYSCTL_STATIC_CHILDREN
237 .Fa "struct sysctl_oid_list OID_NAME"
239 .Ft struct sysctl_oid_list *
240 .Fo SYSCTL_NODE_CHILDREN
244 .Ft struct sysctl_oid *
246 .Fa "struct sysctl_oid *oid"
248 .Fn SYSCTL_INT parent number name ctlflags ptr val descr
249 .Fn SYSCTL_LONG parent number name ctlflags ptr val descr
250 .Fn SYSCTL_NODE parent number name ctlflags handler descr
251 .Fn SYSCTL_OPAQUE parent number name ctlflags ptr len format descr
252 .Fn SYSCTL_PROC parent number name ctlflags arg1 arg2 handler format descr
253 .Fn SYSCTL_QUAD parent number name ctlflags ptr val descr
254 .Fn SYSCTL_STRING parent number name ctlflags arg len descr
255 .Fn SYSCTL_STRUCT parent number name ctlflags ptr struct_type descr
256 .Fn SYSCTL_ROOT_NODE number name ctlflags handler descr
257 .Fn SYSCTL_U8 parent number name ctlflags ptr val descr
258 .Fn SYSCTL_U16 parent number name ctlflags ptr val descr
259 .Fn SYSCTL_UINT parent number name ctlflags ptr val descr
260 .Fn SYSCTL_ULONG parent number name ctlflags ptr val descr
261 .Fn SYSCTL_UQUAD parent number name ctlflags ptr val descr
265 kernel interface allows dynamic or static creation of
268 All static sysctls are automatically destroyed when the module which
269 they are part of is unloaded.
270 Most top level categories are created statically and are available to
271 all kernel code and its modules.
272 .Sh DESCRIPTION OF ARGUMENTS
273 .Bl -tag -width ctlflags
275 Pointer to sysctl context or NULL, if no context.
277 .Xr sysctl_ctx_init 9
278 for how to create a new sysctl context.
279 Programmers are strongly advised to use contexts to organize the
280 dynamic OIDs which they create because when a context is destroyed all
281 belonging sysctls are destroyed as well.
282 This makes the sysctl cleanup code much simpler.
283 Else deletion of all created OIDs is required at module unload.
286 .Li struct sysctl_oid_list ,
287 which is the head of the parent's list of children.
288 This pointer is retrieved using the
289 .Fn SYSCTL_STATIC_CHILDREN
290 macro for static sysctls and the
292 macro for dynamic sysctls.
295 macro can be used to get the parent of an OID.
296 The macro returns NULL if there is no parent.
298 The OID number that will be assigned to this OID.
299 In almost all cases this should be set to
301 which will result in the assignment of the next available OID number.
304 The newly created OID will contain a copy of the name.
306 A bit mask of sysctl control flags.
307 See the section below describing all the control flags.
309 First callback argument for procedure sysctls.
311 Second callback argument for procedure sysctls.
313 The length of the data pointed to by the
316 For string type OIDs a length of zero means that
318 will be used to get the length of the string at each access to the OID.
320 Pointer to sysctl variable or string data.
321 For sysctl values the pointer can be SYSCTL_NULL_XXX_PTR which means the OID is read-only and the returned value should be taken from the
327 argument is SYSCTL_NULL_XXX_PTR, gives the constant value returned by this OID.
328 Else this argument is not used.
330 Name of structure type.
332 A pointer to the function
333 that is responsible for handling read and write requests
335 There are several standard handlers
336 that support operations on nodes,
337 integers, strings and opaque objects.
338 It is possible to define custom handlers using the
344 A pointer to a string
345 which specifies the format of the OID in a symbolic way.
346 This format is used as a hint by
348 to apply proper data formatting for display purposes.
351 .Bl -tag -width "S,TYPE" -compact -offset indent
359 temperature in Kelvin, multiplied by an optional single digit
360 power of ten scaling factor: 1 (default) gives deciKelvin, 0 gives Kelvin, 3
377 A pointer to a textual description of the OID.
379 .Sh CREATING ROOT NODES
380 Sysctl MIBs or OIDs are created in a hierarchical tree.
381 The nodes at the bottom of the tree are called root nodes, and have no
383 To create bottom tree nodes the
386 .Fn SYSCTL_ADD_ROOT_NODE
387 function needs to be used.
388 By default all static sysctl node OIDs are global and need a
390 statement prior to their
392 definition statement, typically in a so-called header file.
393 .Sh CREATING SYSCTL STRINGS
394 Zero terminated character strings sysctls are created either using the
397 .Fn SYSCTL_ADD_STRING
401 argument in zero, the string length is computed at every access to the OID using
403 .Sh CREATING OPAQUE SYSCTLS
409 .Fn SYSCTL_ADD_OPAQUE
411 .Fn SYSCTL_ADD_STRUCT
412 functions create an OID that handle any chunk of data
413 of the size specified by the
415 argument and data pointed to by the
418 When using the structure version the type is encoded as part of the
420 .Sh CREATING CUSTOM SYSCTLS
426 create OIDs with the specified
429 The handler is responsible for handling all read and write requests to
431 This OID type is especially useful if the kernel data is not easily
432 accessible, or needs to be processed before exporting.
433 .Sh CREATING A STATIC SYSCTL
434 Static sysctls are declared using one of the
441 .Fn SYSCTL_ROOT_NODE ,
451 .Sh CREATING A DYNAMIC SYSCTL
452 Dynamic nodes are created using one of the
454 .Fn SYSCTL_ADD_LONG ,
455 .Fn SYSCTL_ADD_NODE ,
456 .Fn SYSCTL_ADD_OPAQUE ,
457 .Fn SYSCTL_ADD_PROC ,
458 .Fn SYSCTL_ADD_QUAD ,
459 .Fn SYSCTL_ADD_ROOT_NODE ,
460 .Fn SYSCTL_ADD_STRING ,
461 .Fn SYSCTL_ADD_STRUCT ,
464 .Fn SYSCTL_ADD_UAUTO ,
465 .Fn SYSCTL_ADD_UINT ,
466 .Fn SYSCTL_ADD_ULONG ,
471 .Xr sysctl_remove_oid 9
473 .Xr sysctl_ctx_free 9
474 for more information on how to destroy a dynamically created OID.
476 For most of the above functions and macros, declaring a type as part
477 of the access flags is not necessary \[em] however, when declaring a
478 sysctl implemented by a function, including a type in the access mask
480 .Bl -tag -width ".Dv CTLTYPE_NOFETCH"
482 This is a node intended to be a parent for other nodes.
484 This is a signed integer.
485 .It Dv CTLTYPE_STRING
486 This is a nul-terminated string stored in a character array.
488 This is a 64-bit signed integer.
489 .It Dv CTLTYPE_OPAQUE
490 This is an opaque data structure.
491 .It Dv CTLTYPE_STRUCT
495 This is an 8-bit unsigned integer.
497 This is a 16-bit unsigned integer.
499 This is an unsigned integer.
501 This is a signed long.
503 This is an unsigned long.
505 This is a 64-bit unsigned integer.
508 All sysctl types except for new node declarations require one of the following
509 flags to be set indicating the read and write disposition of the sysctl:
510 .Bl -tag -width ".Dv CTLFLAG_ANYBODY"
512 This is a read-only sysctl.
514 This is a read-only sysctl and tunable which is tried fetched once
515 from the system enviroment early during module load or system boot.
517 This is a writable sysctl.
519 This sysctl is readable and writable.
521 This is a readable and writeable sysctl and tunable which is tried
522 fetched once from the system enviroment early during module load or
524 .It Dv CTLFLAG_NOFETCH
525 In case the node is marked as a tunable using the CTLFLAG_[XX]TUN,
526 this flag will prevent fetching the initial value from the system
527 environment. Typically this flag should only be used for very early
528 low level system setup code, and not by common drivers and modules.
531 Additionally, any of the following optional flags may also be specified:
532 .Bl -tag -width ".Dv CTLFLAG_ANYBODY"
533 .It Dv CTLFLAG_ANYBODY
534 Any user or process can write to this sysctl.
535 .It Dv CTLFLAG_SECURE
536 This sysctl can be written to only if the effective securelevel of the
538 .It Dv CTLFLAG_PRISON
539 This sysctl can be written to by processes in
542 When iterating the sysctl name space, do not list this sysctl.
544 Advisory flag that a system tunable also exists for this variable.
545 The initial sysctl value is tried fetched once from the system
546 enviroment early during module load or system boot.
548 Dynamically created OIDs automatically get this flag set.
550 OID references a VIMAGE-enabled variable.
557 sysctl tree for use by new nodes:
558 .Bd -literal -offset indent
559 SYSCTL_DECL(_security);
562 Examples of integer, opaque, string, and procedure sysctls follow:
563 .Bd -literal -offset indent
565 * Example of a constant integer value. Notice that the control
566 * flags are CTLFLAG_RD, the variable pointer is SYSCTL_NULL_INT_PTR,
567 * and the value is declared.
569 SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, SYSCTL_NULL_INT_PTR,
570 sizeof(struct bio), "sizeof(struct bio)");
573 * Example of a variable integer value. Notice that the control
574 * flags are CTLFLAG_RW, the variable pointer is set, and the
577 static int doingcache = 1; /* 1 => enable the cache */
578 SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0,
579 "Enable name cache");
582 * Example of a variable string value. Notice that the control
583 * flags are CTLFLAG_RW, that the variable pointer and string
584 * size are set. Unlike newer sysctls, this older sysctl uses a
587 char kernelname[MAXPATHLEN] = "/kernel"; /* XXX bloat */
588 SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW,
589 kernelname, sizeof(kernelname), "Name of kernel file booted");
592 * Example of an opaque data type exported by sysctl. Notice that
593 * the variable pointer and size are provided, as well as a format
594 * string for sysctl(8).
596 static l_fp pps_freq; /* scaled frequence offset (ns/s) */
597 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD,
598 &pps_freq, sizeof(pps_freq), "I", "");
601 * Example of a procedure based sysctl exporting string
602 * information. Notice that the data type is declared, the NULL
603 * variable pointer and 0 size, the function pointer, and the
604 * format string for sysctl(8).
606 SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING |
607 CTLFLAG_RW, NULL, 0, sysctl_kern_timecounter_hardware, "A",
611 The following is an example of
612 how to create a new top-level category
613 and how to hook up another subtree to an existing static node.
614 This example does not use contexts,
615 which results in tedious management of all intermediate oids,
616 as they need to be freed later on:
617 .Bd -literal -offset indent
618 #include <sys/sysctl.h>
621 * Need to preserve pointers to newly created subtrees,
622 * to be able to free them later:
624 static struct sysctl_oid *root1;
625 static struct sysctl_oid *root2;
626 static struct sysctl_oid *oidp;
628 static char *string = "dynamic sysctl";
631 root1 = SYSCTL_ADD_ROOT_NODE(NULL,
632 OID_AUTO, "newtree", CTLFLAG_RW, 0, "new top level tree");
633 oidp = SYSCTL_ADD_INT(NULL, SYSCTL_CHILDREN(root1),
634 OID_AUTO, "newint", CTLFLAG_RW, &a_int, 0, "new int leaf");
636 root2 = SYSCTL_ADD_NODE(NULL, SYSCTL_STATIC_CHILDREN(_debug),
637 OID_AUTO, "newtree", CTLFLAG_RW, 0, "new tree under debug");
638 oidp = SYSCTL_ADD_STRING(NULL, SYSCTL_CHILDREN(root2),
639 OID_AUTO, "newstring", CTLFLAG_RD, string, 0, "new string leaf");
642 This example creates the following subtrees:
643 .Bd -literal -offset indent
644 debug.newtree.newstring
648 .Em "Care should be taken to free all OIDs once they are no longer needed!"
650 When adding, modifying, or removing sysctl names, it is important to be
651 aware that these interfaces may be used by users, libraries, applications,
652 or documentation (such as published books), and are implicitly published application interfaces.
653 As with other application interfaces, caution must be taken not to break
654 existing applications, and to think about future use of new name spaces so as
655 to avoid the need to rename or remove interfaces that might be depended on in
658 The semantics chosen for a new sysctl should be as clear as possible,
659 and the name of the sysctl must closely reflect its semantics.
660 Therefore the sysctl name deserves a fair amount of consideration.
661 It should be short but yet representative of the sysctl meaning.
662 If the name consists of several words, they should be separated by
663 underscore characters, as in
664 .Va compute_summary_at_mount .
665 Underscore characters may be omitted only if the name consists of not more
666 than two words, each being not longer than four characters, as in
668 For boolean sysctls, negative logic should be totally avoided.
669 That is, do not use names like
673 They are confusing and lead to configuration errors.
674 Use positive logic instead:
678 A temporary sysctl node OID that should not be relied upon must be designated
679 as such by a leading underscore character in its name. For example:
684 .Xr sysctl_add_oid 9 ,
685 .Xr sysctl_ctx_free 9 ,
686 .Xr sysctl_ctx_init 9 ,
687 .Xr sysctl_remove_oid 9
691 utility first appeared in
697 implementation originally found in
699 has been extensively rewritten by
700 .An Poul-Henning Kamp
701 in order to add support for name lookups, name space iteration, and dynamic
702 addition of MIB nodes.
704 This man page was written by
705 .An Robert N. M. Watson .
706 .Sh SECURITY CONSIDERATIONS
707 When creating new sysctls, careful attention should be paid to the security
708 implications of the monitoring or management interface being created.
709 Most sysctls present in the kernel are read-only or writable only by the
711 Sysctls exporting extensive information on system data structures and
712 operation, especially those implemented using procedures, will wish to
713 implement access control to limit the undesired exposure of information about
714 other processes, network connections, etc.
716 The following top level sysctl name spaces are commonly used:
717 .Bl -tag -width ".Va regression"
719 Compatibility layer information.
721 Debugging information.
722 Various name spaces exist under
725 Hardware and device driver information.
727 Kernel behavior tuning; generally deprecated in favor of more specific
730 Machine-dependent configuration parameters.
733 Various protocols have name spaces under
736 Regression test configuration and information.
738 Security and security-policy configuration and information.
740 Reserved name space for the implementation of sysctl.
742 Configuration settings relating to user application behavior.
743 Generally, configuring applications using kernel sysctls is discouraged.
745 Virtual file system configuration and information.
747 Virtual memory subsystem configuration and information.