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 ,
42 .Nm SYSCTL_ADD_UAUTO ,
44 .Nm SYSCTL_ADD_ULONG ,
45 .Nm SYSCTL_ADD_UQUAD ,
47 .Nm SYSCTL_STATIC_CHILDREN ,
48 .Nm SYSCTL_NODE_CHILDREN ,
56 .Nm SYSCTL_ROOT_NODE ,
62 .Nd Dynamic and static sysctl MIB creation functions
67 .Ft struct sysctl_oid *
69 .Fa "struct sysctl_ctx_list *ctx"
70 .Fa "struct sysctl_oid_list *parent"
72 .Fa "const char *name"
76 .Fa "const char *descr"
78 .Ft struct sysctl_oid *
80 .Fa "struct sysctl_ctx_list *ctx"
81 .Fa "struct sysctl_oid_list *parent"
83 .Fa "const char *name"
86 .Fa "const char *descr"
88 .Ft struct sysctl_oid *
90 .Fa "struct sysctl_ctx_list *ctx"
91 .Fa "struct sysctl_oid_list *parent"
93 .Fa "const char *name"
95 .Fa "int (*handler)(SYSCTL_HANDLER_ARGS)"
96 .Fa "const char *descr"
98 .Ft struct sysctl_oid *
100 .Fa "struct sysctl_ctx_list *ctx"
101 .Fa "struct sysctl_oid_list *parent"
103 .Fa "const char *name"
107 .Fa "const char *format"
108 .Fa "const char *descr"
110 .Ft struct sysctl_oid *
112 .Fa "struct sysctl_ctx_list *ctx"
113 .Fa "struct sysctl_oid_list *parent"
115 .Fa "const char *name"
119 .Fa "int (*handler) (SYSCTL_HANDLERARGS)"
120 .Fa "const char *format"
121 .Fa "const char *descr"
123 .Ft struct sysctl_oid *
125 .Fa "struct sysctl_ctx_list *ctx"
126 .Fa "struct sysctl_oid_list *parent"
128 .Fa "const char *name"
131 .Fa "const char *descr"
133 .Ft struct sysctl_oid *
134 .Fo SYSCTL_ADD_ROOT_NODE
135 .Fa "struct sysctl_ctx_list *ctx"
137 .Fa "const char *name"
139 .Fa "int (*handler)(SYSCTL_HANDLER_ARGS)"
140 .Fa "const char *descr"
142 .Ft struct sysctl_oid *
143 .Fo SYSCTL_ADD_STRING
144 .Fa "struct sysctl_ctx_list *ctx"
145 .Fa "struct sysctl_oid_list *parent"
147 .Fa "const char *name"
151 .Fa "const char *descr"
153 .Ft struct sysctl_oid *
154 .Fo SYSCTL_ADD_STRUCT
155 .Fa "struct sysctl_ctx_list *ctx"
156 .Fa "struct sysctl_oid_list *parent"
158 .Fa "const char *name"
162 .Fa "const char *descr"
164 .Ft struct sysctl_oid *
166 .Fa "struct sysctl_ctx_list *ctx"
167 .Fa "struct sysctl_oid_list *parent"
169 .Fa "const char *name"
171 .Fa "unsigned int *ptr"
173 .Fa "const char *descr"
175 .Ft struct sysctl_oid *
177 .Fa "struct sysctl_ctx_list *ctx"
178 .Fa "struct sysctl_oid_list *parent"
180 .Fa "const char *name"
182 .Fa "unsigned long *ptr"
183 .Fa "const char *descr"
185 .Ft struct sysctl_oid *
187 .Fa "struct sysctl_ctx_list *ctx"
188 .Fa "struct sysctl_oid_list *parent"
190 .Fa "const char *name"
193 .Fa "const char *descr"
195 .Ft struct sysctl_oid *
197 .Fa "struct sysctl_ctx_list *ctx"
198 .Fa "struct sysctl_oid_list *parent"
200 .Fa "const char *name"
203 .Fa "const char *descr"
205 .Ft struct sysctl_oid_list *
207 .Fa "struct sysctl_oid *oidp"
209 .Ft struct sysctl_oid_list *
210 .Fo SYSCTL_STATIC_CHILDREN
211 .Fa "struct sysctl_oid_list OID_NAME"
213 .Ft struct sysctl_oid_list *
214 .Fo SYSCTL_NODE_CHILDREN
218 .Ft struct sysctl_oid *
220 .Fa "struct sysctl_oid *oid"
222 .Fn SYSCTL_INT parent number name ctlflags ptr val descr
223 .Fn SYSCTL_LONG parent number name ctlflags ptr val descr
224 .Fn SYSCTL_NODE parent number name ctlflags handler descr
225 .Fn SYSCTL_OPAQUE parent number name ctlflags ptr len format descr
226 .Fn SYSCTL_PROC parent number name ctlflags arg1 arg2 handler format descr
227 .Fn SYSCTL_QUAD parent number name ctlflags ptr val descr
228 .Fn SYSCTL_STRING parent number name ctlflags arg len descr
229 .Fn SYSCTL_STRUCT parent number name ctlflags ptr struct_type descr
230 .Fn SYSCTL_ROOT_NODE number name ctlflags handler descr
231 .Fn SYSCTL_UINT parent number name ctlflags ptr val descr
232 .Fn SYSCTL_ULONG parent number name ctlflags ptr val descr
233 .Fn SYSCTL_UQUAD parent number name ctlflags ptr val descr
237 kernel interface allows dynamic or static creation of
240 All static sysctls are automatically destroyed when the module which
241 they are part of is unloaded.
242 Most top level categories are created statically and are available to
243 all kernel code and its modules.
244 .Sh DESCRIPTION OF ARGUMENTS
245 .Bl -tag -width ctlflags
247 Pointer to sysctl context or NULL, if no context.
249 .Xr sysctl_ctx_init 9
250 for how to create a new sysctl context.
251 Programmers are strongly advised to use contexts to organize the
252 dynamic OIDs which they create because when a context is destroyed all
253 belonging sysctls are destroyed as well.
254 This makes the sysctl cleanup code much simpler.
255 Else deletion of all created OIDs is required at module unload.
258 .Li struct sysctl_oid_list ,
259 which is the head of the parent's list of children.
260 This pointer is retrieved using the
261 .Fn SYSCTL_STATIC_CHILDREN
262 macro for static sysctls and the
264 macro for dynamic sysctls.
267 macro can be used to get the parent of an OID.
268 The macro returns NULL if there is no parent.
270 The OID number that will be assigned to this OID.
271 In almost all cases this should be set to
273 which will result in the assignment of the next available OID number.
276 The newly created OID will contain a copy of the name.
278 A bit mask of sysctl control flags.
279 See the section below describing all the control flags.
281 First callback argument for procedure sysctls.
283 Second callback argument for procedure sysctls.
285 The length of the data pointed to by the
288 For string type OIDs a length of zero means that
290 will be used to get the length of the string at each access to the OID.
292 Pointer to sysctl variable or string data.
293 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
299 argument is SYSCTL_NULL_XXX_PTR, gives the constant value returned by this OID.
300 Else this argument is not used.
302 Name of structure type.
304 A pointer to the function
305 that is responsible for handling read and write requests
307 There are several standard handlers
308 that support operations on nodes,
309 integers, strings and opaque objects.
310 It is possible to define custom handlers using the
316 A pointer to a string
317 which specifies the format of the OID in a symbolic way.
318 This format is used as a hint by
320 to apply proper data formatting for display purposes.
323 .Bl -tag -width "S,TYPE" -compact -offset indent
331 temperature in Kelvin, multiplied by an optional single digit
332 power of ten scaling factor: 1 (default) gives deciKelvin, 0 gives Kelvin, 3
349 A pointer to a textual description of the OID.
351 .Sh CREATING ROOT NODES
352 Sysctl MIBs or OIDs are created in a hierarchical tree.
353 The nodes at the bottom of the tree are called root nodes, and have no
355 To create bottom tree nodes the
358 .Fn SYSCTL_ADD_ROOT_NODE
359 function needs to be used.
360 By default all static sysctl node OIDs are global and need a
362 statement prior to their
364 definition statement, typically in a so-called header file.
365 .Sh CREATING SYSCTL STRINGS
366 Zero terminated character strings sysctls are created either using the
369 .Fn SYSCTL_ADD_STRING
373 argument in zero, the string length is computed at every access to the OID using
375 .Sh CREATING OPAQUE SYSCTLS
381 .Fn SYSCTL_ADD_OPAQUE
383 .Fn SYSCTL_ADD_STRUCT
384 functions create an OID that handle any chunk of data
385 of the size specified by the
387 argument and data pointed to by the
390 When using the structure version the type is encoded as part of the
392 .Sh CREATING CUSTOM SYSCTLS
398 create OIDs with the specified
401 The handler is responsible for handling all read and write requests to
403 This OID type is especially useful if the kernel data is not easily
404 accessible, or needs to be processed before exporting.
405 .Sh CREATING A STATIC SYSCTL
406 Static sysctls are declared using one of the
413 .Fn SYSCTL_ROOT_NODE ,
421 .Sh CREATING A DYNAMIC SYSCTL
422 Dynamic nodes are created using one of the
424 .Fn SYSCTL_ADD_LONG ,
425 .Fn SYSCTL_ADD_NODE ,
426 .Fn SYSCTL_ADD_OPAQUE ,
427 .Fn SYSCTL_ADD_PROC ,
428 .Fn SYSCTL_ADD_QUAD ,
429 .Fn SYSCTL_ADD_ROOT_NODE ,
430 .Fn SYSCTL_ADD_STRING ,
431 .Fn SYSCTL_ADD_STRUCT ,
432 .Fn SYSCTL_ADD_UAUTO ,
433 .Fn SYSCTL_ADD_UINT ,
434 .Fn SYSCTL_ADD_ULONG ,
439 .Xr sysctl_remove_oid 9
441 .Xr sysctl_ctx_free 9
442 for more information on how to destroy a dynamically created OID.
444 For most of the above functions and macros, declaring a type as part
445 of the access flags is not necessary \[em] however, when declaring a
446 sysctl implemented by a function, including a type in the access mask
448 .Bl -tag -width ".Dv CTLTYPE_NOFETCH"
450 This is a node intended to be a parent for other nodes.
452 This is a signed integer.
453 .It Dv CTLTYPE_STRING
454 This is a nul-terminated string stored in a character array.
456 This is a 64-bit signed integer.
457 .It Dv CTLTYPE_OPAQUE
458 This is an opaque data structure.
459 .It Dv CTLTYPE_STRUCT
463 This is an unsigned integer.
465 This is a signed long.
467 This is an unsigned long.
469 This is a 64-bit unsigned integer.
472 All sysctl types except for new node declarations require one of the following
473 flags to be set indicating the read and write disposition of the sysctl:
474 .Bl -tag -width ".Dv CTLFLAG_ANYBODY"
476 This is a read-only sysctl.
478 This is a read-only sysctl and tunable which is tried fetched once
479 from the system enviroment early during module load or system boot.
481 This is a writable sysctl.
483 This sysctl is readable and writable.
485 This is a readable and writeable sysctl and tunable which is tried
486 fetched once from the system enviroment early during module load or
488 .It Dv CTLFLAG_NOFETCH
489 In case the node is marked as a tunable using the CTLFLAG_[XX]TUN,
490 this flag will prevent fetching the initial value from the system
491 environment. Typically this flag should only be used for very early
492 low level system setup code, and not by common drivers and modules.
495 Additionally, any of the following optional flags may also be specified:
496 .Bl -tag -width ".Dv CTLFLAG_ANYBODY"
497 .It Dv CTLFLAG_ANYBODY
498 Any user or process can write to this sysctl.
499 .It Dv CTLFLAG_SECURE
500 This sysctl can be written to only if the effective securelevel of the
502 .It Dv CTLFLAG_PRISON
503 This sysctl can be written to by processes in
506 When iterating the sysctl name space, do not list this sysctl.
508 Advisory flag that a system tunable also exists for this variable.
509 The initial sysctl value is tried fetched once from the system
510 enviroment early during module load or system boot.
512 Dynamically created OIDs automatically get this flag set.
514 OID references a VIMAGE-enabled variable.
521 sysctl tree for use by new nodes:
522 .Bd -literal -offset indent
523 SYSCTL_DECL(_security);
526 Examples of integer, opaque, string, and procedure sysctls follow:
527 .Bd -literal -offset indent
529 * Example of a constant integer value. Notice that the control
530 * flags are CTLFLAG_RD, the variable pointer is SYSCTL_NULL_INT_PTR,
531 * and the value is declared.
533 SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, SYSCTL_NULL_INT_PTR,
534 sizeof(struct bio), "sizeof(struct bio)");
537 * Example of a variable integer value. Notice that the control
538 * flags are CTLFLAG_RW, the variable pointer is set, and the
541 static int doingcache = 1; /* 1 => enable the cache */
542 SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0,
543 "Enable name cache");
546 * Example of a variable string value. Notice that the control
547 * flags are CTLFLAG_RW, that the variable pointer and string
548 * size are set. Unlike newer sysctls, this older sysctl uses a
551 char kernelname[MAXPATHLEN] = "/kernel"; /* XXX bloat */
552 SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW,
553 kernelname, sizeof(kernelname), "Name of kernel file booted");
556 * Example of an opaque data type exported by sysctl. Notice that
557 * the variable pointer and size are provided, as well as a format
558 * string for sysctl(8).
560 static l_fp pps_freq; /* scaled frequence offset (ns/s) */
561 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD,
562 &pps_freq, sizeof(pps_freq), "I", "");
565 * Example of a procedure based sysctl exporting string
566 * information. Notice that the data type is declared, the NULL
567 * variable pointer and 0 size, the function pointer, and the
568 * format string for sysctl(8).
570 SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING |
571 CTLFLAG_RW, NULL, 0, sysctl_kern_timecounter_hardware, "A",
575 The following is an example of
576 how to create a new top-level category
577 and how to hook up another subtree to an existing static node.
578 This example does not use contexts,
579 which results in tedious management of all intermediate oids,
580 as they need to be freed later on:
581 .Bd -literal -offset indent
582 #include <sys/sysctl.h>
585 * Need to preserve pointers to newly created subtrees,
586 * to be able to free them later:
588 static struct sysctl_oid *root1;
589 static struct sysctl_oid *root2;
590 static struct sysctl_oid *oidp;
592 static char *string = "dynamic sysctl";
595 root1 = SYSCTL_ADD_ROOT_NODE(NULL,
596 OID_AUTO, "newtree", CTLFLAG_RW, 0, "new top level tree");
597 oidp = SYSCTL_ADD_INT(NULL, SYSCTL_CHILDREN(root1),
598 OID_AUTO, "newint", CTLFLAG_RW, &a_int, 0, "new int leaf");
600 root2 = SYSCTL_ADD_NODE(NULL, SYSCTL_STATIC_CHILDREN(_debug),
601 OID_AUTO, "newtree", CTLFLAG_RW, 0, "new tree under debug");
602 oidp = SYSCTL_ADD_STRING(NULL, SYSCTL_CHILDREN(root2),
603 OID_AUTO, "newstring", CTLFLAG_RD, string, 0, "new string leaf");
606 This example creates the following subtrees:
607 .Bd -literal -offset indent
608 debug.newtree.newstring
612 .Em "Care should be taken to free all OIDs once they are no longer needed!"
614 When adding, modifying, or removing sysctl names, it is important to be
615 aware that these interfaces may be used by users, libraries, applications,
616 or documentation (such as published books), and are implicitly published application interfaces.
617 As with other application interfaces, caution must be taken not to break
618 existing applications, and to think about future use of new name spaces so as
619 to avoid the need to rename or remove interfaces that might be depended on in
622 The semantics chosen for a new sysctl should be as clear as possible,
623 and the name of the sysctl must closely reflect its semantics.
624 Therefore the sysctl name deserves a fair amount of consideration.
625 It should be short but yet representative of the sysctl meaning.
626 If the name consists of several words, they should be separated by
627 underscore characters, as in
628 .Va compute_summary_at_mount .
629 Underscore characters may be omitted only if the name consists of not more
630 than two words, each being not longer than four characters, as in
632 For boolean sysctls, negative logic should be totally avoided.
633 That is, do not use names like
637 They are confusing and lead to configuration errors.
638 Use positive logic instead:
642 A temporary sysctl node OID that should not be relied upon must be designated
643 as such by a leading underscore character in its name. For example:
648 .Xr sysctl_add_oid 9 ,
649 .Xr sysctl_ctx_free 9 ,
650 .Xr sysctl_ctx_init 9 ,
651 .Xr sysctl_remove_oid 9
655 utility first appeared in
661 implementation originally found in
663 has been extensively rewritten by
664 .An Poul-Henning Kamp
665 in order to add support for name lookups, name space iteration, and dynamic
666 addition of MIB nodes.
668 This man page was written by
669 .An Robert N. M. Watson .
670 .Sh SECURITY CONSIDERATIONS
671 When creating new sysctls, careful attention should be paid to the security
672 implications of the monitoring or management interface being created.
673 Most sysctls present in the kernel are read-only or writable only by the
675 Sysctls exporting extensive information on system data structures and
676 operation, especially those implemented using procedures, will wish to
677 implement access control to limit the undesired exposure of information about
678 other processes, network connections, etc.
680 The following top level sysctl name spaces are commonly used:
681 .Bl -tag -width ".Va regression"
683 Compatibility layer information.
685 Debugging information.
686 Various name spaces exist under
689 Hardware and device driver information.
691 Kernel behavior tuning; generally deprecated in favor of more specific
694 Machine-dependent configuration parameters.
697 Various protocols have name spaces under
700 Regression test configuration and information.
702 Security and security-policy configuration and information.
704 Reserved name space for the implementation of sysctl.
706 Configuration settings relating to user application behavior.
707 Generally, configuring applications using kernel sysctls is discouraged.
709 Virtual file system configuration and information.
711 Virtual memory subsystem configuration and information.