SYSCTL_NODE_CHILDREN (9)

Leading comments

Copyright (c) 2006 Robert N. M. Watson
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/o...

(The comments found at the beginning of the groff file "man9/SYSCTL_NODE_CHILDREN.9freebsd".)

NAME

SYSCTL_DECL SYSCTL_ADD_INT SYSCTL_ADD_LONG SYSCTL_ADD_NODE SYSCTL_ADD_OPAQUE SYSCTL_ADD_PROC SYSCTL_ADD_QUAD SYSCTL_ADD_ROOT_NODE SYSCTL_ADD_S8 SYSCTL_ADD_S16 SYSCTL_ADD_S32 SYSCTL_ADD_S64 SYSCTL_ADD_STRING SYSCTL_ADD_STRUCT SYSCTL_ADD_U8 SYSCTL_ADD_U16 SYSCTL_ADD_U32 SYSCTL_ADD_U64 SYSCTL_ADD_UAUTO SYSCTL_ADD_UINT SYSCTL_ADD_ULONG SYSCTL_ADD_UQUAD SYSCTL_CHILDREN SYSCTL_STATIC_CHILDREN SYSCTL_NODE_CHILDREN SYSCTL_PARENT SYSCTL_INT SYSCTL_LONG SYSCTL_NODE SYSCTL_OPAQUE SYSCTL_PROC SYSCTL_QUAD SYSCTL_ROOT_NODE SYSCTL_S8 SYSCTL_S16 SYSCTL_S32 SYSCTL_S64 SYSCTL_STRING SYSCTL_STRUCT SYSCTL_U8 SYSCTL_U16 SYSCTL_U32 SYSCTL_U64 SYSCTL_UINT SYSCTL_ULONG SYSCTL_UQUAD - Dynamic and static sysctl MIB creation functions

SYNOPSIS

In sys/types.h In sys/sysctl.h Fn SYSCTL_DECL name Ft struct sysctl_oid * Fo SYSCTL_ADD_INT Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa int *ptr Fa int val Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_LONG Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa long *ptr Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_NODE Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa int (*handler)(SYSCTL_HANDLER_ARGS) Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_OPAQUE Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa void *ptr Fa intptr_t len Fa const char *format Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_PROC Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa void *arg1 Fa intptr_t arg2 Fa int (*handler) (SYSCTL_HANDLERARGS) Fa const char *format Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_QUAD Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa int64_t *ptr Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_ROOT_NODE Fa struct sysctl_ctx_list *ctx Fa int number Fa const char *name Fa int ctlflags Fa int (*handler)(SYSCTL_HANDLER_ARGS) Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_S8 Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa int8_t *ptr Fa int8_t val Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_S16 Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa int16_t *ptr Fa int16_t val Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_S32 Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa int32_t *ptr Fa int32_t val Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_S64 Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa int64_t *ptr Fa int64_t val Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_STRING Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa char *ptr Fa intptr_t len Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_STRUCT Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa void *ptr Fa struct_type Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_U8 Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa uint8_t *ptr Fa uint8_t val Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_U16 Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa uint16_t *ptr Fa uint16_t val Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_U32 Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa uint32_t *ptr Fa uint32_t val Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_U64 Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa uint64_t *ptr Fa uint64_t val Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_UINT Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa unsigned int *ptr Fa unsigned int val Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_ULONG Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa unsigned long *ptr Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_UQUAD Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa uint64_t *ptr Fa const char *descr Fc Ft struct sysctl_oid * Fo SYSCTL_ADD_UAUTO Fa struct sysctl_ctx_list *ctx Fa struct sysctl_oid_list *parent Fa int number Fa const char *name Fa int ctlflags Fa void *ptr Fa const char *descr Fc Ft struct sysctl_oid_list * Fo SYSCTL_CHILDREN Fa struct sysctl_oid *oidp Fc Ft struct sysctl_oid_list * Fo SYSCTL_STATIC_CHILDREN Fa struct sysctl_oid_list OID_NAME Fc Ft struct sysctl_oid_list * Fo SYSCTL_NODE_CHILDREN Fa parent Fa name Fc Ft struct sysctl_oid * Fo SYSCTL_PARENT Fa struct sysctl_oid *oid Fc Fn SYSCTL_INT parent number name ctlflags ptr val descr Fn SYSCTL_LONG parent number name ctlflags ptr val descr Fn SYSCTL_NODE parent number name ctlflags handler descr Fn SYSCTL_OPAQUE parent number name ctlflags ptr len format descr Fn SYSCTL_PROC parent number name ctlflags arg1 arg2 handler format descr Fn SYSCTL_QUAD parent number name ctlflags ptr val descr Fn SYSCTL_ROOT_NODE number name ctlflags handler descr Fn SYSCTL_S8 parent number name ctlflags ptr val descr Fn SYSCTL_S16 parent number name ctlflags ptr val descr Fn SYSCTL_S32 parent number name ctlflags ptr val descr Fn SYSCTL_S64 parent number name ctlflags ptr val descr Fn SYSCTL_STRING parent number name ctlflags arg len descr Fn SYSCTL_STRUCT parent number name ctlflags ptr struct_type descr Fn SYSCTL_U8 parent number name ctlflags ptr val descr Fn SYSCTL_U16 parent number name ctlflags ptr val descr Fn SYSCTL_U32 parent number name ctlflags ptr val descr Fn SYSCTL_U64 parent number name ctlflags ptr val descr Fn SYSCTL_UINT parent number name ctlflags ptr val descr Fn SYSCTL_ULONG parent number name ctlflags ptr val descr Fn SYSCTL_UQUAD parent number name ctlflags ptr val descr

DESCRIPTION

The SYSCTL kernel interface allows dynamic or static creation of sysctl(8) MIB entries. All static sysctls are automatically destroyed when the module which they are part of is unloaded. Most top level categories are created statically and are available to all kernel code and its modules.

DESCRIPTION OF ARGUMENTS

Fa ctx

Pointer to sysctl context or NULL, if no context. See sysctl_ctx_init9 for how to create a new sysctl context. Programmers are strongly advised to use contexts to organize the dynamic OIDs which they create because when a context is destroyed all belonging sysctls are destroyed as well. This makes the sysctl cleanup code much simpler. Else deletion of all created OIDs is required at module unload.

Fa parent

A pointer to a struct sysctl_oid_list which is the head of the parent's list of children. This pointer is retrieved using the Fn SYSCTL_STATIC_CHILDREN macro for static sysctls and the Fn SYSCTL_CHILDREN macro for dynamic sysctls. The Fn SYSCTL_PARENT macro can be used to get the parent of an OID. The macro returns NULL if there is no parent.

Fa number

The OID number that will be assigned to this OID. In almost all cases this should be set to OID_AUTO which will result in the assignment of the next available OID number.

Fa name

The name of the OID. The newly created OID will contain a copy of the name.

Fa ctlflags

A bit mask of sysctl control flags. See the section below describing all the control flags.

Fa arg1

First callback argument for procedure sysctls.

Fa arg2

Second callback argument for procedure sysctls.

Fa len

The length of the data pointed to by the Fa ptr argument. For string type OIDs a length of zero means that strlen(3) will be used to get the length of the string at each access to the OID.

Fa ptr

Pointer to sysctl variable or string data. For sysctl values the pointer can be SYSCTL_NULL_XXX_PTR which means the OID is read-only and the returned value should be taken from the Fa val argument.

Fa val

If the Fa ptr argument is SYSCTL_NULL_XXX_PTR, gives the constant value returned by this OID. Else this argument is not used.

Fa struct_type

Name of structure type.

Fa handler

A pointer to the function that is responsible for handling read and write requests to this OID. There are several standard handlers that support operations on nodes, integers, strings and opaque objects. It is possible to define custom handlers using the Fn SYSCTL_PROC macro or the Fn SYSCTL_ADD_PROC function.

Fa format

A pointer to a string which specifies the format of the OID in a symbolic way. This format is used as a hint by sysctl(8) to apply proper data formatting for display purposes.

Current formats:

N

node

A

char *

I

int

IK [n ]

temperature in Kelvin, multiplied by an optional single digit power of ten scaling factor: 1 (default) gives deciKelvin, 0 gives Kelvin, 3 gives milliKelvin

IU

unsigned int

L

long

LU

unsigned long

Q

quad_t

QU

u_quad_t

S,TYPE

struct TYPE structures

Fa descr

A pointer to a textual description of the OID.

CREATING ROOT NODES

Sysctl MIBs or OIDs are created in a hierarchical tree. The nodes at the bottom of the tree are called root nodes, and have no parent OID. To create bottom tree nodes the Fn SYSCTL_ROOT_NODE macro or the Fn SYSCTL_ADD_ROOT_NODE function needs to be used. By default all static sysctl node OIDs are global and need a Fn SYSCTL_DECL statement prior to their Fn SYSCTL_NODE definition statement, typically in a so-called header file.

CREATING SYSCTL STRINGS

Zero terminated character strings sysctls are created either using the Fn SYSCTL_STRING macro or the Fn SYSCTL_ADD_STRING function. If the Fa len argument in zero, the string length is computed at every access to the OID using strlen(3).

CREATING OPAQUE SYSCTLS

The Fn SYSCTL_OPAQUE or Fn SYSCTL_STRUCT macros or the Fn SYSCTL_ADD_OPAQUE or Fn SYSCTL_ADD_STRUCT functions create an OID that handle any chunk of data of the size specified by the Fa len argument and data pointed to by the Fa ptr argument. When using the structure version the type is encoded as part of the created sysctl.

CREATING CUSTOM SYSCTLS

The Fn SYSCTL_PROC macro and the Fn SYSCTL_ADD_PROC function create OIDs with the specified handler function. The handler is responsible for handling all read and write requests to the OID. This OID type is especially useful if the kernel data is not easily accessible, or needs to be processed before exporting.

CREATING A STATIC SYSCTL

Static sysctls are declared using one of the Fn SYSCTL_INT , Fn SYSCTL_LONG , Fn SYSCTL_NODE , Fn SYSCTL_OPAQUE , Fn SYSCTL_PROC , Fn SYSCTL_QUAD , Fn SYSCTL_ROOT_NODE , Fn SYSCTL_S8 , Fn SYSCTL_S16 , Fn SYSCTL_S32 , Fn SYSCTL_S64 , Fn SYSCTL_STRING , Fn SYSCTL_STRUCT , Fn SYSCTL_U8 , Fn SYSCTL_U16 , Fn SYSCTL_U32 , Fn SYSCTL_U64 , Fn SYSCTL_UINT , Fn SYSCTL_ULONG or Fn SYSCTL_UQUAD macros.

CREATING A DYNAMIC SYSCTL

Dynamic nodes are created using one of the Fn SYSCTL_ADD_INT , Fn SYSCTL_ADD_LONG , Fn SYSCTL_ADD_NODE , Fn SYSCTL_ADD_OPAQUE , Fn SYSCTL_ADD_PROC , Fn SYSCTL_ADD_QUAD , Fn SYSCTL_ADD_ROOT_NODE , Fn SYSCTL_ADD_S8 , Fn SYSCTL_ADD_S16 , Fn SYSCTL_ADD_S32 , Fn SYSCTL_ADD_S64 , Fn SYSCTL_ADD_STRING , Fn SYSCTL_ADD_STRUCT , Fn SYSCTL_ADD_U8 , Fn SYSCTL_ADD_U16 , Fn SYSCTL_ADD_U32 , Fn SYSCTL_ADD_U64 , Fn SYSCTL_ADD_UAUTO , Fn SYSCTL_ADD_UINT , Fn SYSCTL_ADD_ULONG , or Fn SYSCTL_UQUAD functions. See sysctl_remove_oid9 or sysctl_ctx_free9 for more information on how to destroy a dynamically created OID.

CONTROL FLAGS

For most of the above functions and macros, declaring a type as part of the access flags is not necessary [em] 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 array.

CTLTYPE_S8

This is an 8-bit signed integer.

CTLTYPE_S16

This is a 16-bit signed integer.

CTLTYPE_S32

This is a 32-bit signed integer.

CTLTYPE_S64

This is a 64-bit signed integer.

CTLTYPE_OPAQUE

This is an opaque data structure.

CTLTYPE_STRUCT

Alias for CTLTYPE_OPAQUE

CTLTYPE_U8

This is an 8-bit unsigned integer.

CTLTYPE_U16

This is a 16-bit unsigned integer.

CTLTYPE_U32

This is a 32-bit unsigned integer.

CTLTYPE_U64

This is a 64-bit unsigned integer.

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 of the following flags to be set indicating the read and write disposition of the sysctl:

CTLFLAG_RD

This is a read-only sysctl.

CTLFLAG_RDTUN

This is a read-only sysctl and tunable which is tried fetched once from the system environment early during module load or system boot.

CTLFLAG_WR

This is a writable sysctl.

CTLFLAG_RW

This sysctl is readable and writable.

CTLFLAG_RWTUN

This is a readable and writeable sysctl and tunable which is tried fetched once from the system environment early during module load or system boot.

CTLFLAG_NOFETCH

In case the node is marked as a tunable using the CTLFLAG_[XX]TUN, this flag will prevent fetching the initial value from the system environment. Typically this flag should only be used for very early low level system setup code, and not by common drivers and modules.

Additionally, any of the following optional flags may also be specified:

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 sysctl.

CTLFLAG_TUN

Advisory flag that a system tunable also exists for this variable. The initial sysctl value is tried fetched once from the system environment early during module load or system boot.

CTLFLAG_DYN

Dynamically created OIDs automatically get this flag set.

CTLFLAG_VNET

OID references a VIMAGE-enabled variable.

EXAMPLES

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

SYSCTL_DECL(_security);

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 SYSCTL_NULL_INT_PTR,
 * and the value is declared.
 */
SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, SYSCTL_NULL_INT_PTR,
    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 */
SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW,
    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 frequency 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",
    "");

The following is an example of how to create a new top-level category and how to hook up another subtree to an existing static node. This example does not use contexts, which results in tedious management of all intermediate oids, as they need to be freed later on:

#include <sys/sysctl.h>
 ...
/*
 * Need to preserve pointers to newly created subtrees,
 * to be able to free them later:
 */
static struct sysctl_oid *root1;
static struct sysctl_oid *root2;
static struct sysctl_oid *oidp;
static int a_int;
static char *string = "dynamic sysctl";
 ...

root1 = SYSCTL_ADD_ROOT_NODE(NULL,
        OID_AUTO, "newtree", CTLFLAG_RW, 0, "new top level tree");
oidp = SYSCTL_ADD_INT(NULL, SYSCTL_CHILDREN(root1),
        OID_AUTO, "newint", CTLFLAG_RW, &a_int, 0, "new int leaf");
 ...
root2 = SYSCTL_ADD_NODE(NULL, SYSCTL_STATIC_CHILDREN(_debug),
        OID_AUTO, "newtree", CTLFLAG_RW, 0, "new tree under debug");
oidp = SYSCTL_ADD_STRING(NULL, SYSCTL_CHILDREN(root2),
        OID_AUTO, "newstring", CTLFLAG_RD, string, 0, "new string leaf");

This example creates the following subtrees:

debug.newtree.newstring
newtree.newint

Care should be taken to free all OIDs once they are no longer needed!

SYSCTL NAMING

When adding, modifying, or removing sysctl names, it is important to be aware that these interfaces may be used by users, libraries, applications, 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 OID that should not be relied upon must be designated as such by a leading underscore character in its name. For example: _dirty_hack

SEE ALSO

sysctl(3), sysctl(8), sysctl_add_oid9, sysctl_ctx_free9, sysctl_ctx_init9, sysctl_remove_oid9

HISTORY

The sysctl(8) utility first appeared in BSD 4.4

AUTHORS

An -nosplit The sysctl implementation originally found in BSD has been extensively rewritten by An 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 An Robert N. M. Watson .

SECURITY CONSIDERATIONS

When creating new sysctls, careful attention should be paid to the security implications of the monitoring or management interface being created. 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 debug

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 net

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 discouraged.

vfs

Virtual file system configuration and information.

vm

Virtual memory subsystem configuration and information.