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 November 23, 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.Fn SYSCTL_DECL name 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 60.Sh DESCRIPTION 61The 62.Nm SYSCTL 63kernel interfaces allow code to statically declare 64.Xr sysctl 8 65MIB entries, which will be initialized when the kernel module containing the 66declaration is initialized. 67When the module is unloaded, the sysctl will be automatically destroyed. 68.Pp 69Sysctl nodes are created in a hierarchical tree, with all static nodes being 70represented by named C data structures; in order to create a new node under 71an existing node in the tree, the structure representing the desired parent 72node must be declared in the current context using 73.Fn SYSCTL_DECL . 74.Pp 75New nodes are declared using one of 76.Fn SYSCTL_INT , 77.Fn SYSCTL_LONG , 78.Fn SYSCTL_NODE , 79.Fn SYSCTL_OPAQUE , 80.Fn SYSCTL_PROC , 81.Fn SYSCTL_STRING , 82.Fn SYSCTL_STRUCT , 83.Fn SYSCTL_UINT , 84.Fn SYSCTL_ULONG , 85.Fn SYSCTL_XINT , 86and 87.Fn SYSCTL_XLONG . 88Each macro accepts a parent name, as declared using 89.Fn SYSCTL_DECL , 90an OID number, typically 91.Dv OID_AUTO , 92a node name, a set of control and access flags, and a description. 93Depending on the macro, a pointer to a variable supporting the MIB entry, a 94size, a value, and a function pointer implementing the MIB entry may also be 95present. 96.Pp 97For most of the above macros, declaring a type as part of the access flags is 98not necessary \[em] however, when declaring a sysctl implemented by a function, 99including a type in the access mask is required: 100.Bl -tag -width ".Dv CTLTYPE_STRING" 101.It Dv CTLTYPE_NODE 102This is a node intended to be a parent for other nodes. 103.It Dv CTLTYPE_INT 104This is a signed integer. 105.It Dv CTLTYPE_STRING 106This is a nul-terminated string stored in a character array. 107.It Dv CTLTYPE_QUAD 108This is a 64-bit signed integer. 109.It Dv CTLTYPE_OPAQUE 110This is an opaque data structure. 111.It Dv CTLTYPE_STRUCT 112Alias for 113.Dv CTLTYPE_OPAQUE. 114.It Dv CTLTYPE_UINT 115This is an unsigned integer. 116.It Dv CTLTYPE_LONG 117This is a signed long. 118.It Dv CTLTYPE_ULONG 119This is an unsigned long. 120.El 121.Pp 122All sysctl types except for new node declarations require one or more flags 123to be set indicating the read and write disposition of the sysctl: 124.Bl -tag -width ".Dv CTLFLAG_ANYBODY" 125.It Dv CTLFLAG_RD 126This is a read-only sysctl. 127.It Dv CTLFLAG_WR 128This is a writable sysctl. 129.It Dv CTLFLAG_RW 130This sysctl is readable and writable. 131.It Dv CTLFLAG_ANYBODY 132Any user or process can write to this sysctl. 133.It Dv CTLFLAG_SECURE 134This sysctl can be written to only if the effective securelevel of the 135process is \[<=] 0. 136.It Dv CTLFLAG_PRISON 137This sysctl can be written to by processes in 138.Xr jail 2 . 139.It Dv CTLFLAG_SKIP 140When iterating the sysctl name space, do not list this sysctl. 141.It Dv CTLFLAG_TUN 142Also declare a system tunable with the same name to initialize this variable. 143.It Dv CTLFLAG_RDTUN 144Also declare a system tunable with the same name to initialize this variable; 145however, the run-time variable is read-only. 146.El 147.Pp 148When creating new sysctls, careful attention should be paid to the security 149implications of the monitoring or management interface being created. 150Most sysctls present in the kernel are read-only or writable only by the 151superuser. 152Sysctls exporting extensive information on system data structures and 153operation, especially those implemented using procedures, will wish to 154implement access control to limit the undesired exposure of information about 155other processes, network connections, etc. 156.Pp 157The following top level sysctl name spaces are commonly used: 158.Bl -tag -width ".Va regression" 159.It Va compat 160Compatibility layer information. 161.It Va debug 162Debugging information. 163Various name spaces exist under 164.Va debug . 165.It Va hw 166Hardware and device driver information. 167.It Va kern 168Kernel behavior tuning; generally deprecated in favor of more specific 169name spaces. 170.It Va machdep 171Machine-dependent configuration parameters. 172.It Va net 173Network subsystem. 174Various protocols have name spaces under 175.Va net . 176.It Va regression 177Regression test configuration and information. 178.It Va security 179Security and security-policy configuration and information. 180.It Va sysctl 181Reserved name space for the implementation of sysctl. 182.It Va user 183Configuration settings relating to user application behavior. 184Generally, configuring applications using kernel sysctls is discouraged. 185.It Va vfs 186Virtual file system configuration and information. 187.It Va vm 188Virtual memory subsystem configuration and information. 189.El 190.Sh EXAMPLES 191Sample use of 192.Fn SYSCTL_DECL 193to declare the 194.Va security 195sysctl tree for use by new nodes: 196.Bd -literal -offset indent 197SYSCTL_DECL(_security); 198.Ed 199.Pp 200Examples of integer, opaque, string, and procedure sysctls follow: 201.Bd -literal -offset indent 202/* 203 * Example of a constant integer value. Notice that the control 204 * flags are CTLFLAG_RD, the variable pointer is NULL, and the 205 * value is declared. 206 * If sysctl(8) should print this value in hex, use 'SYSCTL_XINT'. 207 */ 208SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, NULL, 209 sizeof(struct bio), "sizeof(struct bio)"); 210 211/* 212 * Example of a variable integer value. Notice that the control 213 * flags are CTLFLAG_RW, the variable pointer is set, and the 214 * value is 0. 215 */ 216static int doingcache = 1; /* 1 => enable the cache */ 217SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0, 218 "Enable name cache"); 219 220/* 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 224 * static oid number. 225 */ 226char kernelname[MAXPATHLEN] = "/kernel"; /* XXX bloat */ 227SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW, 228 kernelname, sizeof(kernelname), "Name of kernel file booted"); 229 230/* 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). 234 */ 235static l_fp pps_freq; /* scaled frequence offset (ns/s) */ 236SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD, 237 &pps_freq, sizeof(pps_freq), "I", ""); 238 239/* 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). 244 */ 245SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING | 246 CTLFLAG_RW, NULL, 0, sysctl_kern_timecounter_hardware, "A", 247 ""); 248.Ed 249.Sh SYSCTL NAMING 250When adding, modifying, or removing sysctl names, it is important to be 251aware that these interfaces may be used by users, libraries, applications, 252or documentation (such as published books), and are implicitly published application interfaces. 253As with other application interfaces, caution must be taken not to break 254existing applications, and to think about future use of new name spaces so as 255to avoid the need to rename or remove interfaces that might be depended on in 256the future. 257.Pp 258The semantics chosen for a new sysctl should be as clear as possible, 259and the name of the sysctl must closely reflect its semantics. 260Therefore the sysctl name deserves a fair amount of consideration. 261It should be short but yet representative of the sysctl meaning. 262If the name consists of several words, they should be separated by 263underscore characters, as in 264.Va compute_summary_at_mount . 265Underscore characters may be omitted only if the name consists of not more 266than two words, each being not longer than four characters, as in 267.Va bootfile . 268For boolean sysctls, negative logic should be totally avoided. 269That is, do not use names like 270.Va no_foobar 271or 272.Va foobar_disable . 273They are confusing and lead to configuration errors. 274Use positive logic instead: 275.Va foobar , 276.Va foobar_enable . 277.Pp 278A temporary sysctl node that should not be relied upon must be designated 279as such by a leading underscore character in its name. For example: 280.Va _dirty_hack . 281.Sh SEE ALSO 282.Xr sysctl 8 , 283.Xr sysctl_add_oid 9 , 284.Xr sysctl_ctx_free 9 , 285.Xr sysctl_ctx_init 9 , 286.Xr sysctl_remove_oid 9 287.Sh HISTORY 288The 289.Xr sysctl 8 290utility first appeared in 291.Bx 4.4 . 292.Sh AUTHORS 293.An -nosplit 294The 295.Nm sysctl 296implementation originally found in 297.Bx 298has been extensively rewritten by 299.An Poul-Henning Kamp 300in order to add support for name lookups, name space iteration, and dynamic 301addition of MIB nodes. 302.Pp 303This man page was written by 304.An Robert N. M. Watson . 305