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44 .Nd Static sysctl declaration functions
49 .Fn SYSCTL_INT parent nbr name access ptr val descr
50 .Fn SYSCTL_LONG parent nbr name access ptr val descr
51 .Fn SYSCTL_NODE parent nbr name access handler descr
52 .Fn SYSCTL_OPAQUE parent nbr name access ptr len fmt descr
53 .Fn SYSCTL_PROC parent nbr name access ptr arg handler fmt descr
54 .Fn SYSCTL_STRING parent nbr name access arg len descr
55 .Fn SYSCTL_STRUCT parent nbr name access ptr type descr
56 .Fn SYSCTL_UINT parent nbr name access ptr val descr
57 .Fn SYSCTL_ULONG parent nbr name access ptr val descr
58 .Fn SYSCTL_XINT parent nbr name access ptr val descr
59 .Fn SYSCTL_XLONG parent nbr name access ptr val descr
63 kernel interfaces allow code to statically declare
65 MIB entries, which will be initialized when the kernel module containing the
66 declaration is initialized.
67 When the module is unloaded, the sysctl will be automatically destroyed.
69 Sysctl nodes are created in a hierarchical tree, with all static nodes being
70 represented by named C data structures; in order to create a new node under
71 an existing node in the tree, the structure representing the desired parent
72 node must be declared in the current context using
75 New nodes are declared using one of
88 Each macro accepts a parent name, as declared using
90 an OID number, typically
92 a node name, a set of control and access flags, and a description.
93 Depending on the macro, a pointer to a variable supporting the MIB entry, a
94 size, a value, and a function pointer implementing the MIB entry may also be
97 For most of the above macros, declaring a type as part of the access flags is
98 not necessary \[em] however, when declaring a sysctl implemented by a function,
99 including a type in the access mask is required:
100 .Bl -tag -width ".Dv CTLTYPE_STRING"
102 This is a node intended to be a parent for other nodes.
104 This is a signed integer.
105 .It Dv CTLTYPE_STRING
106 This is a nul-terminated string stored in a character array.
108 This is a 64-bit signed integer.
109 .It Dv CTLTYPE_OPAQUE
110 This is an opaque data structure.
111 .It Dv CTLTYPE_STRUCT
115 This is an unsigned integer.
117 This is a signed long.
119 This is an unsigned long.
122 All sysctl types except for new node declarations require one or more flags
123 to be set indicating the read and write disposition of the sysctl:
124 .Bl -tag -width ".Dv CTLFLAG_ANYBODY"
126 This is a read-only sysctl.
128 This is a writable sysctl.
130 This sysctl is readable and writable.
131 .It Dv CTLFLAG_ANYBODY
132 Any user or process can write to this sysctl.
133 .It Dv CTLFLAG_SECURE
134 This sysctl can be written to only if the effective securelevel of the
136 .It Dv CTLFLAG_PRISON
137 This sysctl can be written to by processes in
140 When iterating the sysctl name space, do not list this sysctl.
142 Also declare a system tunable with the same name to initialize this variable.
144 Also declare a system tunable with the same name to initialize this variable;
145 however, the run-time variable is read-only.
148 When creating new sysctls, careful attention should be paid to the security
149 implications of the monitoring or management interface being created.
150 Most sysctls present in the kernel are read-only or writable only by the
152 Sysctls exporting extensive information on system data structures and
153 operation, especially those implemented using procedures, will wish to
154 implement access control to limit the undesired exposure of information about
155 other processes, network connections, etc.
157 The following top level sysctl name spaces are commonly used:
158 .Bl -tag -width ".Va regression"
160 Compatibility layer information.
162 Debugging information.
163 Various name spaces exist under
166 Hardware and device driver information.
168 Kernel behavior tuning; generally deprecated in favor of more specific
171 Machine-dependent configuration parameters.
174 Various protocols have name spaces under
177 Regression test configuration and information.
179 Security and security-policy configuration and information.
181 Reserved name space for the implementation of sysctl.
183 Configuration settings relating to user application behavior.
184 Generally, configuring applications using kernel sysctls is discouraged.
186 Virtual file system configuration and information.
188 Virtual memory subsystem configuration and information.
195 sysctl tree for use by new nodes:
196 .Bd -literal -offset indent
197 SYSCTL_DECL(_security);
200 Examples of integer, opaque, string, and procedure sysctls follow:
201 .Bd -literal -offset indent
203 * Example of a constant integer value. Notice that the control
204 * flags are CTLFLAG_RD, the variable pointer is NULL, and the
206 * If sysctl(8) should print this value in hex, use 'SYSCTL_XINT'.
208 SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, NULL,
209 sizeof(struct bio), "sizeof(struct bio)");
212 * Example of a variable integer value. Notice that the control
213 * flags are CTLFLAG_RW, the variable pointer is set, and the
216 static int doingcache = 1; /* 1 => enable the cache */
217 SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0,
218 "Enable name cache");
221 * Example of a variable string value. Notice that the control
222 * flags are CTLFLAG_RW, that the variable pointer and string
223 * size are set. Unlike newer sysctls, this older sysctl uses a
226 char kernelname[MAXPATHLEN] = "/kernel"; /* XXX bloat */
227 SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW,
228 kernelname, sizeof(kernelname), "Name of kernel file booted");
231 * Example of an opaque data type exported by sysctl. Notice that
232 * the variable pointer and size are provided, as well as a format
233 * string for sysctl(8).
235 static l_fp pps_freq; /* scaled frequence offset (ns/s) */
236 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD,
237 &pps_freq, sizeof(pps_freq), "I", "");
240 * Example of a procedure based sysctl exporting string
241 * information. Notice that the data type is declared, the NULL
242 * variable pointer and 0 size, the function pointer, and the
243 * format string for sysctl(8).
245 SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING |
246 CTLFLAG_RW, NULL, 0, sysctl_kern_timecounter_hardware, "A",
250 When adding, modifying, or removing sysctl names, it is important to be
251 aware that these interfaces may be used by users, libraries, applications,
252 or documentation (such as published books), and are implicitly published application interfaces.
253 As with other application interfaces, caution must be taken not to break
254 existing applications, and to think about future use of new name spaces so as
255 to avoid the need to rename or remove interfaces that might be depended on in
258 The semantics chosen for a new sysctl should be as clear as possible,
259 and the name of the sysctl must closely reflect its semantics.
260 Therefore the sysctl name deserves a fair amount of consideration.
261 It should be short but yet representative of the sysctl meaning.
262 If the name consists of several words, they should be separated by
263 underscore characters, as in
264 .Va compute_summary_at_mount .
265 Underscore characters may be omitted only if the name consists of not more
266 than two words, each being not longer than four characters, as in
268 For boolean sysctls, negative logic should be totally avoided.
269 That is, do not use names like
273 They are confusing and lead to configuration errors.
274 Use positive logic instead:
278 A temporary sysctl node that should not be relied upon must be designated
279 as such by a leading underscore character in its name. For example:
283 .Xr sysctl_add_oid 9 ,
284 .Xr sysctl_ctx_free 9 ,
285 .Xr sysctl_ctx_init 9 ,
286 .Xr sysctl_remove_oid 9
290 utility first appeared in
296 implementation originally found in
298 has been extensively rewritten by
299 .An Poul-Henning Kamp
300 in order to add support for name lookups, name space iteration, and dynamic
301 addition of MIB nodes.
303 This man page was written by
304 .An Robert N. M. Watson .