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