SYSCTL_INT man page on FreeBSD

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SYSCTL(9)		 BSD Kernel Developer's Manual		     SYSCTL(9)

     SYSCTL_XINT, SYSCTL_XLONG, SYSCTL_QUAD — Static sysctl declaration func‐

     #include <sys/types.h>
     #include <sys/sysctl.h>


     SYSCTL_INT(parent, nbr, name, access, ptr, val, descr);

     SYSCTL_LONG(parent, nbr, name, access, ptr, val, descr);

     SYSCTL_NODE(parent, nbr, name, access, handler, descr);

     SYSCTL_OPAQUE(parent, nbr, name, access, ptr, len, fmt, descr);

     SYSCTL_PROC(parent, nbr, name, access, ptr, arg, handler, fmt, descr);

     SYSCTL_STRING(parent, nbr, name, access, arg, len, descr);

     SYSCTL_STRUCT(parent, nbr, name, access, ptr, type, descr);

     SYSCTL_UINT(parent, nbr, name, access, ptr, val, descr);

     SYSCTL_ULONG(parent, nbr, name, access, ptr, val, descr);

     SYSCTL_XINT(parent, nbr, name, access, ptr, val, descr);

     SYSCTL_XLONG(parent, nbr, name, access, ptr, val, descr);

     SYSCTL_QUAD(parent, nbr, name, access, ptr, val, descr);

     The SYSCTL kernel interfaces allow code to statically declare sysctl(8)
     MIB entries, which will be initialized when the kernel module containing
     the declaration is initialized.  When the module is unloaded, the sysctl
     will be automatically destroyed.

     Sysctl nodes are created in a hierarchical tree, with all static nodes
     being represented by named C data structures; in order to create a new
     node under an existing node in the tree, the structure representing the
     desired parent node must be declared in the current context using

     New nodes are declared using one of SYSCTL_INT(), SYSCTL_LONG(),
     SYSCTL_XLONG(), and SYSCTL_QUAD().	 Each macro accepts a parent name, as
     declared using SYSCTL_DECL(), an OID number, typically OID_AUTO, a node
     name, a set of control and access flags, and a description.  Depending on
     the macro, a pointer to a variable supporting the MIB entry, a size, a
     value, and a function pointer implementing the MIB entry may also be

     For most of the above macros, declaring a type as part of the access
     flags is not necessary — however, when declaring a sysctl implemented by
     a function, including a type in the access mask is required:

     CTLTYPE_NODE    This is a node intended to be a parent for other nodes.

     CTLTYPE_INT     This is a signed integer.

     CTLTYPE_STRING  This is a nul-terminated string stored in a character

     CTLTYPE_QUAD    This is a 64-bit signed integer.

     CTLTYPE_OPAQUE  This is an opaque data structure.


     CTLTYPE_UINT    This is an unsigned integer.

     CTLTYPE_LONG    This is a signed long.

     CTLTYPE_ULONG   This is an unsigned long.

     All sysctl types except for new node declarations require one or more
     flags to be set indicating the read and write disposition of the sysctl:

     CTLFLAG_RD	      This is a read-only sysctl.

     CTLFLAG_WR	      This is a writable sysctl.

     CTLFLAG_RW	      This sysctl is readable and writable.

     CTLFLAG_ANYBODY  Any user or process can write to this sysctl.

     CTLFLAG_SECURE   This sysctl can be written to only if the effective
		      securelevel of the process is ≤ 0.

     CTLFLAG_PRISON   This sysctl can be written to by processes in jail(2).

     CTLFLAG_SKIP     When iterating the sysctl name space, do not list this

     CTLFLAG_TUN      Also declare a system tunable with the same name to ini‐
		      tialize this variable.

     CTLFLAG_RDTUN    Also declare a system tunable with the same name to ini‐
		      tialize this variable; however, the run-time variable is

     When creating new sysctls, careful attention should be paid to the secu‐
     rity implications of the monitoring or management interface being cre‐
     ated.  Most sysctls present in the kernel are read-only or writable only
     by the superuser.	Sysctls exporting extensive information on system data
     structures and operation, especially those implemented using procedures,
     will wish to implement access control to limit the undesired exposure of
     information about other processes, network connections, etc.

     The following top level sysctl name spaces are commonly used:

     compat	 Compatibility layer information.

     debug	 Debugging information.	 Various name spaces exist under

     hw		 Hardware and device driver information.

     kern	 Kernel behavior tuning; generally deprecated in favor of more
		 specific name spaces.

     machdep	 Machine-dependent configuration parameters.

     net	 Network subsystem.  Various protocols have name spaces under

     regression	 Regression test configuration and information.

     security	 Security and security-policy configuration and information.

     sysctl	 Reserved name space for the implementation of sysctl.

     user	 Configuration settings relating to user application behavior.
		 Generally, configuring applications using kernel sysctls is

     vfs	 Virtual file system configuration and information.

     vm		 Virtual memory subsystem configuration and information.

     Sample use of SYSCTL_DECL() to declare the security sysctl tree for use
     by new nodes:


     Examples of integer, opaque, string, and procedure sysctls follow:

	    * Example of a constant integer value.  Notice that the control
	    * flags are CTLFLAG_RD, the variable pointer is NULL, and the
	    * value is declared.
	    * If sysctl(8) should print this value in hex, use 'SYSCTL_XINT'.
	   SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, NULL,
	       sizeof(struct bio), "sizeof(struct bio)");

	    * Example of a variable integer value.  Notice that the control
	    * flags are CTLFLAG_RW, the variable pointer is set, and the
	    * value is 0.
	   static int	   doingcache = 1;	   /* 1 => enable the cache */
	   SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0,
	       "Enable name cache");

	    * Example of a variable string value.  Notice that the control
	    * flags are CTLFLAG_RW, that the variable pointer and string
	    * size are set.  Unlike newer sysctls, this older sysctl uses a
	    * static oid number.
	   char kernelname[MAXPATHLEN] = "/kernel";	   /* XXX bloat */
	       kernelname, sizeof(kernelname), "Name of kernel file booted");

	    * Example of an opaque data type exported by sysctl.  Notice that
	    * the variable pointer and size are provided, as well as a format
	    * string for sysctl(8).
	   static l_fp pps_freq;   /* scaled frequence offset (ns/s) */
	   SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD,
	       &pps_freq, sizeof(pps_freq), "I", "");

	    * Example of a procedure based sysctl exporting string
	    * information.  Notice that the data type is declared, the NULL
	    * variable pointer and 0 size, the function pointer, and the
	    * format string for sysctl(8).
	   SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING |
	       CTLFLAG_RW, NULL, 0, sysctl_kern_timecounter_hardware, "A",

     When adding, modifying, or removing sysctl names, it is important to be
     aware that these interfaces may be used by users, libraries, applica‐
     tions, or documentation (such as published books), and are implicitly
     published application interfaces.	As with other application interfaces,
     caution must be taken not to break existing applications, and to think
     about future use of new name spaces so as to avoid the need to rename or
     remove interfaces that might be depended on in the future.

     The semantics chosen for a new sysctl should be as clear as possible, and
     the name of the sysctl must closely reflect its semantics.	 Therefore the
     sysctl name deserves a fair amount of consideration.  It should be short
     but yet representative of the sysctl meaning.  If the name consists of
     several words, they should be separated by underscore characters, as in
     compute_summary_at_mount.	Underscore characters may be omitted only if
     the name consists of not more than two words, each being not longer than
     four characters, as in bootfile.  For boolean sysctls, negative logic
     should be totally avoided.	 That is, do not use names like no_foobar or
     foobar_disable.  They are confusing and lead to configuration errors.
     Use positive logic instead: foobar, foobar_enable.

     A temporary sysctl node that should not be relied upon must be designated
     as such by a leading underscore character in its name.  For example:

     sysctl(8), sysctl_add_oid(9), sysctl_ctx_free(9), sysctl_ctx_init(9),

     The sysctl(8) utility first appeared in 4.4BSD.

     The sysctl implementation originally found in BSD has been extensively
     rewritten by Poul-Henning Kamp in order to add support for name lookups,
     name space iteration, and dynamic addition of MIB nodes.

     This man page was written by Robert N. M. Watson.

BSD			       November 23, 2006			   BSD

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