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.Nm SYSCTL_XINT , 43.Nm SYSCTL_XLONG 44.Nd Static sysctl declaration functions 45.Sh SYNOPSIS 46.In sys/types.h 47.In sys/sysctl.h 48.Fo SYSCTL_DECL 49.Fa "name" 50.Fc 51.Fo SYSCTL_INT 52.Fa "parent" 53.Fa "nbr" 54.Fa "name" 55.Fa "access" 56.Fa "ptr" 57.Fa "val" 58.Fa "descr" 59.Fc 60.Fo SYSCTL_LONG 61.Fa "parent" 62.Fa "nbr" 63.Fa "name" 64.Fa "access" 65.Fa "ptr" 66.Fa "val" 67.Fa "descr" 68.Fc 69.Fo SYSCTL_NODE 70.Fa "parent" 71.Fa "nbr" 72.Fa "name" 73.Fa "access" 74.Fa "handler" 75.Fa "descr" 76.Fc 77.Fo SYSCTL_OPAQUE 78.Fa "parent" 79.Fa "nbr" 80.Fa "name" 81.Fa "access" 82.Fa "ptr" 83.Fa "len" 84.Fa "fmt" 85.Fa "descr" 86.Fc 87.Fo SYSCTL_PROC 88.Fa "parent" 89.Fa "nbr" 90.Fa "name" 91.Fa "access" 92.Fa "ptr" 93.Fa "arg" 94.Fa "handler" 95.Fa "fmt" 96.Fa "descr" 97.Fc 98.Fo SYSCTL_STRING 99.Fa "parent" 100.Fa "nbr" 101.Fa "name" 102.Fa "access" 103.Fa "arg" 104.Fa "len" 105.Fa "descr" 106.Fc 107.Fo SYSCTL_STRUCT 108.Fa "parent" 109.Fa "nbr" 110.Fa "name" 111.Fa "access" 112.Fa "ptr" 113.Fa "type" 114.Fa "descr" 115.Fc 116.Fo SYSCTL_UINT 117.Fa "parent" 118.Fa "nbr" 119.Fa "name" 120.Fa "access" 121.Fa "ptr" 122.Fa "val" 123.Fa "descr" 124.Fc 125.Fo SYSCTL_ULONG 126.Fa "parent" 127.Fa "nbr" 128.Fa "name" 129.Fa "access" 130.Fa "ptr" 131.Fa "val" 132.Fa "descr" 133.Fc 134.Fo SYSCTL_XINT 135.Fa "parent" 136.Fa "nbr" 137.Fa "name" 138.Fa "access" 139.Fa "ptr" 140.Fa "val" 141.Fa "descr" 142.Fc 143.Fo SYSCTL_XLONG 144.Fa "parent" 145.Fa "nbr" 146.Fa "name" 147.Fa "access" 148.Fa "ptr" 149.Fa "val" 150.Fa "descr" 151.Fc 152.Sh DESCRIPTION 153The 154.Nm 155kernel interfaces allow code to statically declare 156.Xr sysctl 8 157MIB entries, which will be initialized when the kernel module containing the 158declaration is initialized. 159When the module is unloaded, the sysctl will be automatically destroyed. 160.Pp 161Sysctl nodes are created in a hierarchical tree, with all static nodes being 162represented by named C data structures; in order to create a new node under 163an existing node in the tree, the structure representing the desired parent 164node must be declared in the current context using 165.Fn SYSCTL_DECL . 166.Pp 167New nodes are declared using one of 168.Nm SYSCTL_INT , 169.Nm SYSCTL_LONG , 170.Nm SYSCTL_NODE , 171.Nm SYSCTL_OPAQUE , 172.Nm SYSCTL_PROC , 173.Nm SYSCTL_STRING , 174.Nm SYSCTL_STRUCT , 175.Nm SYSCTL_UINT , 176.Nm SYSCTL_ULONG , 177.Nm SYSCTL_XINT , 178and 179.Nm SYSCTL_XLONG . 180Each macro accepts a parent name, as declared using 181.Nm SYSCTL_DECL , 182an OID number, typically 183.Dv OID_AUTO , 184a node name, a set of control and access flags, and a description. 185Depending on the macro, a pointer to a variable supporting the MIB entry, a 186size, a value, and a function pointer implementing the MIB entry may also be 187present. 188.Pp 189For most of the above macros, declaring a type as part of the access flags is 190not necessary -- however, when declaring a sysctl implemented by a function, 191including a type in the access mask is required: 192.Bl -tag -width CTLTYPE_STRING 193.It Dv CTLTYPE_NODE 194This is a node intended to be a parent for other nodes. 195.It Dv CTLTYPE_INT 196This is a signed integer. 197.It Dv CTLTYPE_STRING 198This is a nul-terminated string stored in a character array. 199.It Dv CTLTYPE_QUAD 200This is a 64-bit signed integer. 201.It Dv CTLTYPE_OPAQUE 202This is an opaque data structure. 203.It Dv CTLTYPE_STRUCT 204Alias for 205.Dv CTLTYPE_OPAQUE. 206.It Dv CTLTYPE_UINT 207This is an unsigned integer. 208.It Dv CTLTYPE_LONG 209This is a signed long. 210.It Dv CTLTYPE_ULONG 211This is an unsigned long. 212.El 213.Pp 214All sysctl types except for new node declarations require one or more flags 215to be set indicating the read and write disposition of the sysctl: 216.Bl -tag -width CTLFLAG_ANYBODY 217.It Dv CTLFLAG_RD 218This is a read-only sysctl. 219.It Dv CTLFLAG_WR 220This is a writable sysctl. 221.It Dv CTLFLAG_RW 222This sysctl is readable and writable. 223.It Dv CTLFLAG_ANYBODY 224Any user or process can write to this sysctl. 225.It Dv CTLFLAG_SECURE 226This sysctl can be written to only if the effective securelevel of the 227process is <= 0. 228.It Dv CTLFLAG_PRISON 229This sysctl can be written to by processes in 230.Xr jail 2 . 231.It Dv CTLFLAG_SKIP 232When iterating the sysctl name space, do not list this sysctl. 233.It Dv CTLFLAG_TUN 234Also declare a system tunable with the same name to initialize this variable. 235.It Dv CTLFLAG_RDTUN 236Also declare a system tunable with the same name to initalize this variable; 237however, the run-time variable is read-only. 238.El 239.Pp 240When creating new sysctls, careful attention should be paid to the security 241implications of the monitoring or management interface being created. 242Most sysctls present in the kernel are read-only or writable only by the 243superuser. 244Sysctls exporting extensive information on system data structures and 245operation, especially those implemented using procedures, will wish to 246implement access control to limit the undesired exposure of information about 247other processes, network connections, etc. 248.Pp 249The following top level sysctl name spaces are commonly used: 250.Bl -tag -width regression 251.It Dv compat 252Compatibility layer information. 253.It Dv debug 254Debugging information. 255Various name spaces exist under 256.Dv debug . 257.It Dv hw 258Hardware and device driver information. 259.It Dv kern 260Kernel behavior tuning; generally deprecated in favor of more specific 261name spaces. 262.It Dv machdep 263Machine-dependent configuration parameters. 264.It Dv net 265Network subsystem. 266Various protocols have name spaces under 267.Dv net . 268.It Dv regression 269Regression test configuration and information. 270.It Dv security 271Security and security-policy configuration and information. 272.It Dv sysctl 273Reserved name space for the implementation of sysctl. 274.It Dv user 275Configuration settings relating to user application behavior. 276Generally, configuring applications using kernel sysctls is discouraged. 277.It Dv vfs 278Virtual file system configuration and information. 279.It Dv vm 280Virtual memory subsystem configuration and information. 281.El 282.Sh EXAMPLES 283Sample use of 284.Nm SYSCTL_DECL 285to declare the "security" sysctl tree for use by new nodes: 286.Bd -literal -offset indent 287SYSCTL_DECL(_security); 288.Ed 289.Pp 290Examples of integer, opaque, string, and procedure sysctls follow: 291.Bd -literal -offset indent 292/* 293 * Example of a constant integer value. Notice that the control 294 * flags are CTLFLAG_RD, the variable pointer is NULL, and the 295 * value is declared. 296 * If sysctl(8) should print this value in hex, use 'SYSCTL_XINT'. 297 */ 298SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, NULL, 299 sizeof(struct bio), "sizeof(struct bio)"); 300 301/* 302 * Example of a variable integer value. Notice that the control 303 * flags are CTLFLAG_RW, the variable pointer is set, and the 304 * value is 0. 305 */ 306static int doingcache = 1; /* 1 => enable the cache */ 307SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0, 308 "Enable name cache"); 309 310/* 311 * Example of a variable string value. Notice that the control 312 * flags are CTLFLAG_RW, that the variable pointer and string 313 * size are set. Unlike newer sysctls, this older sysctl uses a 314 * static oid number. 315 */ 316char kernelname[MAXPATHLEN] = "/kernel"; /* XXX bloat */ 317SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW, 318 kernelname, sizeof(kernelname), "Name of kernel file booted"); 319 320/* 321 * Example of an opaque data type exported by sysctl. Notice that 322 * the variable pointer and size are provided, as well as a format 323 * string for sysctl(8). 324 */ 325static l_fp pps_freq; /* scaled frequence offset (ns/s) */ 326SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD, 327 &pps_freq, sizeof(pps_freq), "I", ""); 328 329/* 330 * Example of a procedure based sysctl exporting string 331 * information. Notice that the data type is declared, the NULL 332 * variable pointer and 0 size, the function pointer, and the 333 * format string for sysctl(8). 334 */ 335SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING | 336 CTLFLAG_RW, NULL, 0, sysctl_kern_timecounter_hardware, "A", 337 ""); 338.Ed 339.Pp 340When adding, modifying, or removing sysctl names, it is important to be 341aware that these interfaces may be used by users, libraries, applications, 342or documentation (such as published books), and are implicitly published application interfaces. 343As with other application interfaces, caution must be taken not to break 344existing applications, and to think about future use of new name spaces so as 345to avoid the need to rename or remove interfaces that might be depended on in 346the future. 347.Sh SEE ALSO 348.Xr sysctl 8 , 349.Xr sysctl_add_oid 9 , 350.Xr sysctl_ctx_free 9 , 351.Xr sysctl_ctx_init 9 , 352.Xr sysctl_remove_oid 9 353.Sh HISTORY 354.Xr sysctl 8 355first appeared in 356.Bx 4.4 . 357.Sh AUTHORS 358The sysctl implementation originally found in 359.Bx 360has been extensively rewritten by 361.An Poul-Henning Kamp 362in order to add support for name lookups, name space iteration, and dynamic 363addition of MIB nodes. 364.Pp 365This man page was written by 366.An Robert N. M. Watson . 367