2 .\" Copyright (c) 2006 Robert N. M. Watson
3 .\" All rights reserved.
5 .\" Redistribution and use in source and binary forms, with or without
6 .\" modification, are permitted provided that the following conditions
8 .\" 1. Redistributions of source code must retain the above copyright
9 .\" notice, this list of conditions and the following disclaimer.
10 .\" 2. Redistributions in binary form must reproduce the above copyright
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12 .\" documentation and/or other materials provided with the distribution.
14 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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36 .Nm SYSCTL_ADD_OPAQUE ,
39 .Nm SYSCTL_ADD_ROOT_NODE ,
44 .Nm SYSCTL_ADD_STRING ,
45 .Nm SYSCTL_ADD_CONST_STRING ,
46 .Nm SYSCTL_ADD_STRUCT ,
51 .Nm SYSCTL_ADD_UAUTO ,
53 .Nm SYSCTL_ADD_ULONG ,
54 .Nm SYSCTL_ADD_UQUAD ,
56 .Nm SYSCTL_STATIC_CHILDREN ,
57 .Nm SYSCTL_NODE_CHILDREN ,
65 .Nm SYSCTL_ROOT_NODE ,
71 .Nm SYSCTL_CONST_STRING ,
80 .Nd Dynamic and static sysctl MIB creation functions
85 .Ft struct sysctl_oid *
87 .Fa "struct sysctl_ctx_list *ctx"
88 .Fa "struct sysctl_oid_list *parent"
90 .Fa "const char *name"
94 .Fa "const char *descr"
96 .Ft struct sysctl_oid *
98 .Fa "struct sysctl_ctx_list *ctx"
99 .Fa "struct sysctl_oid_list *parent"
101 .Fa "const char *name"
104 .Fa "const char *descr"
106 .Ft struct sysctl_oid *
108 .Fa "struct sysctl_ctx_list *ctx"
109 .Fa "struct sysctl_oid_list *parent"
111 .Fa "const char *name"
113 .Fa "int (*handler)(SYSCTL_HANDLER_ARGS)"
114 .Fa "const char *descr"
116 .Ft struct sysctl_oid *
117 .Fo SYSCTL_ADD_OPAQUE
118 .Fa "struct sysctl_ctx_list *ctx"
119 .Fa "struct sysctl_oid_list *parent"
121 .Fa "const char *name"
125 .Fa "const char *format"
126 .Fa "const char *descr"
128 .Ft struct sysctl_oid *
130 .Fa "struct sysctl_ctx_list *ctx"
131 .Fa "struct sysctl_oid_list *parent"
133 .Fa "const char *name"
137 .Fa "int (*handler) (SYSCTL_HANDLERARGS)"
138 .Fa "const char *format"
139 .Fa "const char *descr"
141 .Ft struct sysctl_oid *
143 .Fa "struct sysctl_ctx_list *ctx"
144 .Fa "struct sysctl_oid_list *parent"
146 .Fa "const char *name"
149 .Fa "const char *descr"
151 .Ft struct sysctl_oid *
152 .Fo SYSCTL_ADD_ROOT_NODE
153 .Fa "struct sysctl_ctx_list *ctx"
155 .Fa "const char *name"
157 .Fa "int (*handler)(SYSCTL_HANDLER_ARGS)"
158 .Fa "const char *descr"
160 .Ft struct sysctl_oid *
162 .Fa "struct sysctl_ctx_list *ctx"
163 .Fa "struct sysctl_oid_list *parent"
165 .Fa "const char *name"
169 .Fa "const char *descr"
171 .Ft struct sysctl_oid *
173 .Fa "struct sysctl_ctx_list *ctx"
174 .Fa "struct sysctl_oid_list *parent"
176 .Fa "const char *name"
180 .Fa "const char *descr"
182 .Ft struct sysctl_oid *
184 .Fa "struct sysctl_ctx_list *ctx"
185 .Fa "struct sysctl_oid_list *parent"
187 .Fa "const char *name"
191 .Fa "const char *descr"
193 .Ft struct sysctl_oid *
195 .Fa "struct sysctl_ctx_list *ctx"
196 .Fa "struct sysctl_oid_list *parent"
198 .Fa "const char *name"
202 .Fa "const char *descr"
204 .Ft struct sysctl_oid *
205 .Fo SYSCTL_ADD_STRING
206 .Fa "struct sysctl_ctx_list *ctx"
207 .Fa "struct sysctl_oid_list *parent"
209 .Fa "const char *name"
213 .Fa "const char *descr"
215 .Ft struct sysctl_oid *
216 .Fo SYSCTL_ADD_CONST_STRING
217 .Fa "struct sysctl_ctx_list *ctx"
218 .Fa "struct sysctl_oid_list *parent"
220 .Fa "const char *name"
222 .Fa "const char *ptr"
223 .Fa "const char *descr"
225 .Ft struct sysctl_oid *
226 .Fo SYSCTL_ADD_STRUCT
227 .Fa "struct sysctl_ctx_list *ctx"
228 .Fa "struct sysctl_oid_list *parent"
230 .Fa "const char *name"
234 .Fa "const char *descr"
236 .Ft struct sysctl_oid *
238 .Fa "struct sysctl_ctx_list *ctx"
239 .Fa "struct sysctl_oid_list *parent"
241 .Fa "const char *name"
245 .Fa "const char *descr"
247 .Ft struct sysctl_oid *
249 .Fa "struct sysctl_ctx_list *ctx"
250 .Fa "struct sysctl_oid_list *parent"
252 .Fa "const char *name"
256 .Fa "const char *descr"
258 .Ft struct sysctl_oid *
260 .Fa "struct sysctl_ctx_list *ctx"
261 .Fa "struct sysctl_oid_list *parent"
263 .Fa "const char *name"
267 .Fa "const char *descr"
269 .Ft struct sysctl_oid *
271 .Fa "struct sysctl_ctx_list *ctx"
272 .Fa "struct sysctl_oid_list *parent"
274 .Fa "const char *name"
278 .Fa "const char *descr"
280 .Ft struct sysctl_oid *
282 .Fa "struct sysctl_ctx_list *ctx"
283 .Fa "struct sysctl_oid_list *parent"
285 .Fa "const char *name"
287 .Fa "unsigned int *ptr"
288 .Fa "unsigned int val"
289 .Fa "const char *descr"
291 .Ft struct sysctl_oid *
293 .Fa "struct sysctl_ctx_list *ctx"
294 .Fa "struct sysctl_oid_list *parent"
296 .Fa "const char *name"
298 .Fa "unsigned long *ptr"
299 .Fa "const char *descr"
301 .Ft struct sysctl_oid *
303 .Fa "struct sysctl_ctx_list *ctx"
304 .Fa "struct sysctl_oid_list *parent"
306 .Fa "const char *name"
309 .Fa "const char *descr"
311 .Ft struct sysctl_oid *
313 .Fa "struct sysctl_ctx_list *ctx"
314 .Fa "struct sysctl_oid_list *parent"
316 .Fa "const char *name"
319 .Fa "const char *descr"
321 .Ft struct sysctl_oid_list *
323 .Fa "struct sysctl_oid *oidp"
325 .Ft struct sysctl_oid_list *
326 .Fo SYSCTL_STATIC_CHILDREN
327 .Fa "struct sysctl_oid_list OID_NAME"
329 .Ft struct sysctl_oid_list *
330 .Fo SYSCTL_NODE_CHILDREN
334 .Ft struct sysctl_oid *
336 .Fa "struct sysctl_oid *oid"
338 .Fn SYSCTL_INT parent number name ctlflags ptr val descr
339 .Fn SYSCTL_LONG parent number name ctlflags ptr val descr
340 .Fn SYSCTL_NODE parent number name ctlflags handler descr
341 .Fn SYSCTL_OPAQUE parent number name ctlflags ptr len format descr
342 .Fn SYSCTL_PROC parent number name ctlflags arg1 arg2 handler format descr
343 .Fn SYSCTL_QUAD parent number name ctlflags ptr val descr
344 .Fn SYSCTL_ROOT_NODE number name ctlflags handler descr
345 .Fn SYSCTL_S8 parent number name ctlflags ptr val descr
346 .Fn SYSCTL_S16 parent number name ctlflags ptr val descr
347 .Fn SYSCTL_S32 parent number name ctlflags ptr val descr
348 .Fn SYSCTL_S64 parent number name ctlflags ptr val descr
349 .Fn SYSCTL_STRING parent number name ctlflags arg len descr
350 .Fn SYSCTL_CONST_STRING parent number name ctlflags arg descr
351 .Fn SYSCTL_STRUCT parent number name ctlflags ptr struct_type descr
352 .Fn SYSCTL_U8 parent number name ctlflags ptr val descr
353 .Fn SYSCTL_U16 parent number name ctlflags ptr val descr
354 .Fn SYSCTL_U32 parent number name ctlflags ptr val descr
355 .Fn SYSCTL_U64 parent number name ctlflags ptr val descr
356 .Fn SYSCTL_UINT parent number name ctlflags ptr val descr
357 .Fn SYSCTL_ULONG parent number name ctlflags ptr val descr
358 .Fn SYSCTL_UQUAD parent number name ctlflags ptr val descr
362 kernel interface allows dynamic or static creation of
365 All static sysctls are automatically destroyed when the module which
366 they are part of is unloaded.
367 Most top level categories are created statically and are available to
368 all kernel code and its modules.
369 .Sh DESCRIPTION OF ARGUMENTS
370 .Bl -tag -width ctlflags
372 Pointer to sysctl context or NULL, if no context.
374 .Xr sysctl_ctx_init 9
375 for how to create a new sysctl context.
376 Programmers are strongly advised to use contexts to organize the
377 dynamic OIDs which they create because when a context is destroyed all
378 belonging sysctls are destroyed as well.
379 This makes the sysctl cleanup code much simpler.
380 Else deletion of all created OIDs is required at module unload.
383 .Li struct sysctl_oid_list ,
384 which is the head of the parent's list of children.
385 This pointer is retrieved using the
386 .Fn SYSCTL_STATIC_CHILDREN
387 macro for static sysctls and the
389 macro for dynamic sysctls.
392 macro can be used to get the parent of an OID.
393 The macro returns NULL if there is no parent.
395 The OID number that will be assigned to this OID.
396 In almost all cases this should be set to
398 which will result in the assignment of the next available OID number.
401 The newly created OID will contain a copy of the name.
403 A bit mask of sysctl control flags.
404 See the section below describing all the control flags.
406 First callback argument for procedure sysctls.
408 Second callback argument for procedure sysctls.
410 The length of the data pointed to by the
413 For string type OIDs a length of zero means that
415 will be used to get the length of the string at each access to the OID.
417 Pointer to sysctl variable or string data.
418 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
424 argument is SYSCTL_NULL_XXX_PTR, gives the constant value returned by this OID.
425 Else this argument is not used.
427 Name of structure type.
429 A pointer to the function
430 that is responsible for handling read and write requests
432 There are several standard handlers
433 that support operations on nodes,
434 integers, strings and opaque objects.
435 It is possible to define custom handlers using the
441 A pointer to a string
442 which specifies the format of the OID in a symbolic way.
443 This format is used as a hint by
445 to apply proper data formatting for display purposes.
448 .Bl -tag -width "S,TYPE" -compact -offset indent
456 temperature in Kelvin, multiplied by an optional single digit
457 power of ten scaling factor: 1 (default) gives deciKelvin, 0 gives Kelvin, 3
474 A pointer to a textual description of the OID.
476 .Sh CREATING ROOT NODES
477 Sysctl MIBs or OIDs are created in a hierarchical tree.
478 The nodes at the bottom of the tree are called root nodes, and have no
480 To create bottom tree nodes the
483 .Fn SYSCTL_ADD_ROOT_NODE
484 function needs to be used.
485 By default all static sysctl node OIDs are global and need a
487 statement prior to their
489 definition statement, typically in a so-called header file.
490 .Sh CREATING SYSCTL STRINGS
491 Zero terminated character strings sysctls are created either using the
494 .Fn SYSCTL_ADD_STRING
498 argument in zero, the string length is computed at every access to the OID using
501 .Fn SYSCTL_CONST_STRING
503 .Fn SYSCTL_ADD_CONST_STRING
504 function to add a sysctl for a constant string.
505 .Sh CREATING OPAQUE SYSCTLS
511 .Fn SYSCTL_ADD_OPAQUE
513 .Fn SYSCTL_ADD_STRUCT
514 functions create an OID that handle any chunk of data
515 of the size specified by the
517 argument and data pointed to by the
520 When using the structure version the type is encoded as part of the
522 .Sh CREATING CUSTOM SYSCTLS
528 create OIDs with the specified
531 The handler is responsible for handling all read and write requests to
533 This OID type is especially useful if the kernel data is not easily
534 accessible, or needs to be processed before exporting.
535 .Sh CREATING A STATIC SYSCTL
536 Static sysctls are declared using one of the
543 .Fn SYSCTL_ROOT_NODE ,
549 .Fn SYSCTL_CONST_STRING ,
560 .Sh CREATING A DYNAMIC SYSCTL
561 Dynamic nodes are created using one of the
563 .Fn SYSCTL_ADD_LONG ,
564 .Fn SYSCTL_ADD_NODE ,
565 .Fn SYSCTL_ADD_OPAQUE ,
566 .Fn SYSCTL_ADD_PROC ,
567 .Fn SYSCTL_ADD_QUAD ,
568 .Fn SYSCTL_ADD_ROOT_NODE ,
573 .Fn SYSCTL_ADD_STRING ,
574 .Fn SYSCTL_ADD_CONST_STRING ,
575 .Fn SYSCTL_ADD_STRUCT ,
580 .Fn SYSCTL_ADD_UAUTO ,
581 .Fn SYSCTL_ADD_UINT ,
582 .Fn SYSCTL_ADD_ULONG ,
587 .Xr sysctl_remove_oid 9
589 .Xr sysctl_ctx_free 9
590 for more information on how to destroy a dynamically created OID.
592 For most of the above functions and macros, declaring a type as part
593 of the access flags is not necessary \[em] however, when declaring a
594 sysctl implemented by a function, including a type in the access mask
596 .Bl -tag -width ".Dv CTLTYPE_NOFETCH"
598 This is a node intended to be a parent for other nodes.
600 This is a signed integer.
601 .It Dv CTLTYPE_STRING
602 This is a nul-terminated string stored in a character array.
604 This is an 8-bit signed integer.
606 This is a 16-bit signed integer.
608 This is a 32-bit signed integer.
610 This is a 64-bit signed integer.
611 .It Dv CTLTYPE_OPAQUE
612 This is an opaque data structure.
613 .It Dv CTLTYPE_STRUCT
617 This is an 8-bit unsigned integer.
619 This is a 16-bit unsigned integer.
621 This is a 32-bit unsigned integer.
623 This is a 64-bit unsigned integer.
625 This is an unsigned integer.
627 This is a signed long.
629 This is an unsigned long.
632 All sysctl types except for new node declarations require one of the following
633 flags to be set indicating the read and write disposition of the sysctl:
634 .Bl -tag -width ".Dv CTLFLAG_ANYBODY"
636 This is a read-only sysctl.
638 This is a read-only sysctl and tunable which is tried fetched once
639 from the system environment early during module load or system boot.
641 This is a writable sysctl.
643 This sysctl is readable and writable.
645 This is a readable and writeable sysctl and tunable which is tried
646 fetched once from the system environment early during module load or
648 .It Dv CTLFLAG_NOFETCH
649 In case the node is marked as a tunable using the CTLFLAG_[XX]TUN,
650 this flag will prevent fetching the initial value from the system
652 Typically this flag should only be used for very early
653 low level system setup code, and not by common drivers and modules.
656 Additionally, any of the following optional flags may also be specified:
657 .Bl -tag -width ".Dv CTLFLAG_ANYBODY"
658 .It Dv CTLFLAG_ANYBODY
659 Any user or process can write to this sysctl.
661 A process in capability mode can read from this sysctl.
663 A process in capability mode can write to this sysctl.
664 .It Dv CTLFLAG_SECURE
665 This sysctl can be written to only if the effective securelevel of the
667 .It Dv CTLFLAG_PRISON
668 This sysctl can be written to by processes in
671 When iterating the sysctl name space, do not list this sysctl.
673 Advisory flag that a system tunable also exists for this variable.
674 The initial sysctl value is tried fetched once from the system
675 environment early during module load or system boot.
677 Dynamically created OIDs automatically get this flag set.
679 OID references a VIMAGE-enabled variable.
686 sysctl tree for use by new nodes:
687 .Bd -literal -offset indent
688 SYSCTL_DECL(_security);
691 Examples of integer, opaque, string, and procedure sysctls follow:
692 .Bd -literal -offset indent
694 * Example of a constant integer value. Notice that the control
695 * flags are CTLFLAG_RD, the variable pointer is SYSCTL_NULL_INT_PTR,
696 * and the value is declared.
698 SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, SYSCTL_NULL_INT_PTR,
699 sizeof(struct bio), "sizeof(struct bio)");
702 * Example of a variable integer value. Notice that the control
703 * flags are CTLFLAG_RW, the variable pointer is set, and the
706 static int doingcache = 1; /* 1 => enable the cache */
707 SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0,
708 "Enable name cache");
711 * Example of a variable string value. Notice that the control
712 * flags are CTLFLAG_RW, that the variable pointer and string
713 * size are set. Unlike newer sysctls, this older sysctl uses a
716 char kernelname[MAXPATHLEN] = "/kernel"; /* XXX bloat */
717 SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW,
718 kernelname, sizeof(kernelname), "Name of kernel file booted");
721 * Example of an opaque data type exported by sysctl. Notice that
722 * the variable pointer and size are provided, as well as a format
723 * string for sysctl(8).
725 static l_fp pps_freq; /* scaled frequency offset (ns/s) */
726 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD,
727 &pps_freq, sizeof(pps_freq), "I", "");
730 * Example of a procedure based sysctl exporting string
731 * information. Notice that the data type is declared, the NULL
732 * variable pointer and 0 size, the function pointer, and the
733 * format string for sysctl(8).
735 SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING |
736 CTLFLAG_RW, NULL, 0, sysctl_kern_timecounter_hardware, "A",
740 The following is an example of
741 how to create a new top-level category
742 and how to hook up another subtree to an existing static node.
743 This example does not use contexts,
744 which results in tedious management of all intermediate oids,
745 as they need to be freed later on:
746 .Bd -literal -offset indent
747 #include <sys/sysctl.h>
750 * Need to preserve pointers to newly created subtrees,
751 * to be able to free them later:
753 static struct sysctl_oid *root1;
754 static struct sysctl_oid *root2;
755 static struct sysctl_oid *oidp;
757 static char *string = "dynamic sysctl";
760 root1 = SYSCTL_ADD_ROOT_NODE(NULL,
761 OID_AUTO, "newtree", CTLFLAG_RW, 0, "new top level tree");
762 oidp = SYSCTL_ADD_INT(NULL, SYSCTL_CHILDREN(root1),
763 OID_AUTO, "newint", CTLFLAG_RW, &a_int, 0, "new int leaf");
765 root2 = SYSCTL_ADD_NODE(NULL, SYSCTL_STATIC_CHILDREN(_debug),
766 OID_AUTO, "newtree", CTLFLAG_RW, 0, "new tree under debug");
767 oidp = SYSCTL_ADD_STRING(NULL, SYSCTL_CHILDREN(root2),
768 OID_AUTO, "newstring", CTLFLAG_RD, string, 0, "new string leaf");
771 This example creates the following subtrees:
772 .Bd -literal -offset indent
773 debug.newtree.newstring
777 .Em "Care should be taken to free all OIDs once they are no longer needed!"
779 When adding, modifying, or removing sysctl names, it is important to be
780 aware that these interfaces may be used by users, libraries, applications,
781 or documentation (such as published books), and are implicitly published application interfaces.
782 As with other application interfaces, caution must be taken not to break
783 existing applications, and to think about future use of new name spaces so as
784 to avoid the need to rename or remove interfaces that might be depended on in
787 The semantics chosen for a new sysctl should be as clear as possible,
788 and the name of the sysctl must closely reflect its semantics.
789 Therefore the sysctl name deserves a fair amount of consideration.
790 It should be short but yet representative of the sysctl meaning.
791 If the name consists of several words, they should be separated by
792 underscore characters, as in
793 .Va compute_summary_at_mount .
794 Underscore characters may be omitted only if the name consists of not more
795 than two words, each being not longer than four characters, as in
797 For boolean sysctls, negative logic should be totally avoided.
798 That is, do not use names like
802 They are confusing and lead to configuration errors.
803 Use positive logic instead:
807 A temporary sysctl node OID that should not be relied upon must be designated
808 as such by a leading underscore character in its name.
814 .Xr sysctl_add_oid 9 ,
815 .Xr sysctl_ctx_free 9 ,
816 .Xr sysctl_ctx_init 9 ,
817 .Xr sysctl_remove_oid 9
821 utility first appeared in
827 implementation originally found in
829 has been extensively rewritten by
830 .An Poul-Henning Kamp
831 in order to add support for name lookups, name space iteration, and dynamic
832 addition of MIB nodes.
834 This man page was written by
835 .An Robert N. M. Watson .
836 .Sh SECURITY CONSIDERATIONS
837 When creating new sysctls, careful attention should be paid to the security
838 implications of the monitoring or management interface being created.
839 Most sysctls present in the kernel are read-only or writable only by the
841 Sysctls exporting extensive information on system data structures and
842 operation, especially those implemented using procedures, will wish to
843 implement access control to limit the undesired exposure of information about
844 other processes, network connections, etc.
846 The following top level sysctl name spaces are commonly used:
847 .Bl -tag -width ".Va regression"
849 Compatibility layer information.
851 Debugging information.
852 Various name spaces exist under
855 Hardware and device driver information.
857 Kernel behavior tuning; generally deprecated in favor of more specific
860 Machine-dependent configuration parameters.
863 Various protocols have name spaces under
866 Regression test configuration and information.
868 Security and security-policy configuration and information.
870 Reserved name space for the implementation of sysctl.
872 Configuration settings relating to user application behavior.
873 Generally, configuring applications using kernel sysctls is discouraged.
875 Virtual file system configuration and information.
877 Virtual memory subsystem configuration and information.