1.\" 2.\" Copyright (c) 2006 Robert N. M. Watson 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 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 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 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 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.\" $FreeBSD$ 27.\" 28.Dd April 28, 2006 29.Dt SYSCTL 9 30.Os 31.Sh NAME 32.Nm SYSCTL_DECL , 33.Nm SYSCTL_INT , 34.Nm SYSCTL_LONG , 35.Nm SYSCTL_NODE , 36.Nm SYSCTL_OPAQUE , 37.Nm SYSCTL_PROC , 38.Nm SYSCTL_STRING , 39.Nm SYSCTL_STRUCT , 40.Nm SYSCTL_UINT , 41.Nm SYSCTL_ULONG 42.Nd Static sysctl declaration functions 43.Sh SYNOPSIS 44.In sys/types.h 45.In sys/sysctl.h 46.Fo SYSCTL_DECL 47.Fa "name" 48.Fc 49.Fo SYSCTL_INT 50.Fa "parent" 51.Fa "nbr" 52.Fa "name" 53.Fa "access" 54.Fa "ptr" 55.Fa "val" 56.Fa "descr" 57.Fc 58.Fo SYSCTL_LONG 59.Fa "parent" 60.Fa "nbr" 61.Fa "name" 62.Fa "access" 63.Fa "ptr" 64.Fa "val" 65.Fa "descr" 66.Fc 67.Fo SYSCTL_NODE 68.Fa "parent" 69.Fa "nbr" 70.Fa "name" 71.Fa "access" 72.Fa "handler" 73.Fa "descr" 74.Fc 75.Fo SYSCTL_OPAQUE 76.Fa "parent" 77.Fa "nbr" 78.Fa "name" 79.Fa "access" 80.Fa "ptr" 81.Fa "len" 82.Fa "fmt" 83.Fa "descr" 84.Fc 85.Fo SYSCTL_PROC 86.Fa "parent" 87.Fa "nbr" 88.Fa "name" 89.Fa "access" 90.Fa "ptr" 91.Fa "arg" 92.Fa "handler" 93.Fa "fmt" 94.Fa "descr" 95.Fc 96.Fo SYSCTL_STRING 97.Fa "parent" 98.Fa "nbr" 99.Fa "name" 100.Fa "access" 101.Fa "arg" 102.Fa "len" 103.Fa "descr" 104.Fc 105.Fo SYSCTL_STRUCT 106.Fa "parent" 107.Fa "nbr" 108.Fa "name" 109.Fa "access" 110.Fa "ptr" 111.Fa "type" 112.Fa "descr" 113.Fc 114.Fo SYSCTL_UINT 115.Fa "parent" 116.Fa "nbr" 117.Fa "name" 118.Fa "access" 119.Fa "ptr" 120.Fa "val" 121.Fa "descr" 122.Fc 123.Fo SYSCTL_ULONG 124.Fa "parent" 125.Fa "nbr" 126.Fa "name" 127.Fa "access" 128.Fa "ptr" 129.Fa "val" 130.Fa "descr" 131.Fc 132.Sh DESCRIPTION 133The 134.Nm 135kernel interfaces allow code to statically declare 136.Xr sysctl 8 137MIB entries, which will be initialized when the kernel module containing the 138declaration is initialized. 139When the module is unloaded, the sysctl will be automatically destroyed. 140.Pp 141Sysctl nodes are created in a hierarchical tree, with all static nodes being 142represented by named C data structures; in order to create a new node under 143an existing node in the tree, the structure representing the desired parent 144node must be declared in the current context using 145.Fn SYSCTL_DECL . 146.Pp 147New nodes are declared using one of 148.Nm SYSCTL_INT , 149.Nm SYSCTL_LONG , 150.Nm SYSCTL_NODE , 151.Nm SYSCTL_OPAQUE , 152.Nm SYSCTL_PROC , 153.Nm SYSCTL_STRING , 154.Nm SYSCTL_STRUCT , 155.Nm SYSCTL_UINT , 156and 157.Nm SYSCTL_ULONG . 158Each macro accepts a parent name, as declared using 159.Nm SYSCTL_DECL , 160an OID number, typically 161.Dv OID_AUTO , 162a node name, a set of control and access flags, and a description. 163Depending on the macro, a pointer to a variable supporting the MIB entry, a 164size, a value, and a function pointer implementing the MIB entry may also be 165present. 166.Pp 167For most of the above macros, declaring a type as part of the access flags is 168not necessary -- however, when declaring a sysctl implemented by a function, 169including a type in the access mask is required: 170.Bl -tag -width CTLTYPE_STRING 171.It Dv CTLTYPE_NODE 172This is a node intended to be a parent for other nodes. 173.It Dv CTLTYPE_INT 174This is a signed integer. 175.It Dv CTLTYPE_STRING 176This is a nul-terminated string stored in a character array. 177.It Dv CTLTYPE_QUAD 178This is a 64-bit signed integer. 179.It Dv CTLTYPE_OPAQUE 180This is an opaque data structure. 181.It Dv CTLTYPE_STRUCT 182Alias for 183.Dv CTLTYPE_OPAQUE. 184.It Dv CTLTYPE_UINT 185This is an unsigned integer. 186.It Dv CTLTYPE_LONG 187This is a signed long. 188.It Dv CTLTYPE_ULONG 189This is an unsigned long. 190.El 191.Pp 192All sysctl types except for new node declarations require one or more flags 193to be set indicating the read and write disposition of the sysctl: 194.Bl -tag -width CTLFLAG_ANYBODY 195.It Dv CTLFLAG_RD 196This is a read-only sysctl. 197It Dv CTLFLAG_WR 198This is a writable sysctl. 199.It Dv CTLFLAG_RW 200This sysctl is readable and writable. 201.It Dv CTLFLAG_ANYBODY 202Any user or process can write to this sysctl. 203.It Dv CTLFLAG_SECURE 204This sysctl can be written to only if the effective securelevel of the 205process is <= 0. 206.It Dv CTLFLAG_PRISON 207This sysctl can be written to by processes in 208.Xr jail 2 . 209.It Dv CTLFLAG_SKIP 210When iterating the sysctl name space, do not list this sysctl. 211.It Dv CTLFLAG_TUN 212Also declare a system tunable with the same name to initialize this variable. 213.It Dv CTLFLAG_RDTUN 214Also declare a system tunable with the same name to initalize this variable; 215however, the run-time variable is read-only. 216.El 217.Pp 218When creating new sysctls, careful attention should be paid to the security 219implications of the monitoring or management interface being created. 220Most sysctls present in the kernel are read-only or writable only by the 221superuser. 222Sysctls exporting extensive information on system data structures and 223operation, especially those implemented using procedures, will wish to 224implement access control to limit the undesired exposure of information about 225other processes, network connections, etc. 226.Pp 227The following top level sysctl name spaces are commonly used: 228.Bl -tag -width regression 229.It Dv compat 230Compatibility layer information. 231.It Dv debug 232Debugging information. 233Various name spaces exist under 234.Dv debug . 235.It Dv hw 236Hardware and device driver information. 237.It Dv kern 238Kernel behavior tuning; generally deprecated in favor of more specific 239name spaces. 240.It Dv machdep 241Machine-dependent configuration parameters. 242.It Dv net 243Network subsystem. 244Various protocols have name spaces under 245.Dv net . 246.It Dv regression 247Regression test configuration and information. 248.It Dv security 249Security and security-policy configuration and information. 250.It Dv sysctl 251Reserved name space for the implementation of sysctl. 252.It Dv user 253Configuration settings relating to user application behavior. 254Generally, configuring applications using kernel sysctls is discouraged. 255.It Dv vfs 256Virtual file system configuration and information. 257.It Dv vm 258Virtual memory subsystem configuration and information. 259.El 260.Sh EXAMPLES 261Sample use of 262.Nm SYSCTL_DECL 263to declare the "security" sysctl tree for use by new nodes: 264.Bd -literal -offset indent 265SYSCTL_DECL(_security); 266.Ed 267.Pp 268Examples of integer, opaque, string, and procedure sysctls follow: 269.Bd -literal -offset indent 270/* 271 * Example of a constant integer value. Notice that the control 272 * flags are CTLFLAG_RD, the variable pointer is NULL, and the 273 * value is declared. 274 */ 275SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, NULL, 276 sizeof(struct bio), "sizeof(struct bio)"); 277 278/* 279 * Example of a variable integer value. Notice that the control 280 * flags are CTLFLAG_RW, the variable pointer is set, and the 281 * value is 0. 282 */ 283static int doingcache = 1; /* 1 => enable the cache */ 284SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0, 285 "Enable name cache"); 286 287/* 288 * Example of a variable string value. Notice that the control 289 * flags are CTLFLAG_RW, that the variable pointer and string 290 * size are set. Unlike newer sysctls, this older sysctl uses a 291 * static oid number. 292 */ 293char kernelname[MAXPATHLEN] = "/kernel"; /* XXX bloat */ 294SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW, 295 kernelname, sizeof(kernelname), "Name of kernel file booted"); 296 297/* 298 * Example of an opaque data type exported by sysctl. Notice that 299 * the variable pointer and size are provided, as well as a format 300 * string for sysctl(8). 301 */ 302static l_fp pps_freq; /* scaled frequence offset (ns/s) */ 303SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD, 304 &pps_freq, sizeof(pps_freq), "I", ""); 305 306/* 307 * Example of a procedure based sysctl exporting string 308 * information. Notice that the data type is declared, the NULL 309 * variable pointer and 0 size, the function pointer, and the 310 * format string for sysctl(8). 311 */ 312SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING | 313 CTLFLAG_RW, NULL, 0, sysctl_kern_timecounter_hardware, "A", 314 ""); 315.Ed 316.Pp 317When adding, modifying, or removing sysctl names, it is important to be 318aware that these interfaces may be used by users, libraries, applications, 319or documentation (such as published books), and are implicitly published application interfaces. 320As with other application interfaces, caution must be taken not to break 321existing applications, and to think about future use of new name spaces so as 322to avoid the need to rename or remove interfaces that might be depended on in 323the future. 324.Sh SEE ALSO 325.Xr sysctl 8 , 326.Xr sysctl_add_oid 9 , 327.Xr sysctl_ctx_free 9 , 328.Xr sysctl_ctx_init 9 , 329.Xr sysctl_remove_oid 9 330.Sh HISTORY 331.Xr sysctl 8 332first appeared in 333.Bx 4.4 . 334.Sh AUTHORS 335The sysctl implementation originally found in 336.Bx 337has been extensively rewritten by 338.An Poul-Henning Kamp 339in order to add support for name lookups, name space iteration, and dynamic 340addition of MIB nodes. 341.Pp 342This man page was written by 343.An Robert N. M. Watson . 344