SYSCTL(9) FreeBSD Kernel Developer's Manual SYSCTL(9)
NAME
SYSCTL_DECL, SYSCTL_ADD_BOOL, SYSCTL_ADD_COUNTER_U64,
SYSCTL_ADD_COUNTER_U64_ARRAY, SYSCTL_ADD_INT, SYSCTL_ADD_LONG,
SYSCTL_ADD_NODE, SYSCTL_ADD_NODE_WITH_LABEL, 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_SBINTIME_MSEC,
SYSCTL_ADD_SBINTIME_USEC, SYSCTL_ADD_STRING, SYSCTL_ADD_CONST_STRING,
SYSCTL_ADD_STRUCT, SYSCTL_ADD_TIMEVAL_SEC, SYSCTL_ADD_U8, SYSCTL_ADD_U16,
SYSCTL_ADD_U32, SYSCTL_ADD_U64, SYSCTL_ADD_UAUTO, SYSCTL_ADD_UINT,
SYSCTL_ADD_ULONG, SYSCTL_ADD_UMA_CUR, SYSCTL_ADD_UMA_MAX,
SYSCTL_ADD_UQUAD, SYSCTL_CHILDREN, SYSCTL_STATIC_CHILDREN,
SYSCTL_NODE_CHILDREN, SYSCTL_PARENT, SYSCTL_BOOL, SYSCTL_COUNTER_U64,
SYSCTL_COUNTER_U64_ARRAY, SYSCTL_INT, SYSCTL_INT_WITH_LABEL, SYSCTL_LONG,
sysctl_msec_to_ticks, SYSCTL_NODE, SYSCTL_NODE_WITH_LABEL, SYSCTL_OPAQUE,
SYSCTL_PROC, SYSCTL_QUAD, SYSCTL_ROOT_NODE, SYSCTL_S8, SYSCTL_S16,
SYSCTL_S32, SYSCTL_S64, SYSCTL_SBINTIME_MSEC, SYSCTL_SBINTIME_USEC,
SYSCTL_STRING, SYSCTL_CONST_STRING, SYSCTL_STRUCT, SYSCTL_TIMEVAL_SEC,
SYSCTL_U8, SYSCTL_U16, SYSCTL_U32, SYSCTL_U64, SYSCTL_UINT, SYSCTL_ULONG,
SYSCTL_UMA_CUR, SYSCTL_UMA_MAX, SYSCTL_UQUAD - Dynamic and static sysctl
MIB creation functions
SYNOPSIS
#include <sys/param.h>
#include <sys/sysctl.h>
SYSCTL_DECL(name);
struct sysctl_oid *
SYSCTL_ADD_BOOL(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, bool *ptr, uint8_t val, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_COUNTER_U64(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, counter_u64_t *ptr, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_COUNTER_U64_ARRAY(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, counter_u64_t *ptr, intmax_t len, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_INT(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, int *ptr, int val, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_LONG(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, long *ptr, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_NODE(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, int (*handler)(SYSCTL_HANDLER_ARGS),)(SYSCTL_HANDLER_ARGS),
const char *descr);
struct sysctl_oid *
SYSCTL_ADD_NODE_WITH_LABEL(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, int (*handler)(SYSCTL_HANDLER_ARGS), const char *descr,)(SYSCTL_HANDLER_ARGS), const char *descr,
const char *label);
struct sysctl_oid *
SYSCTL_ADD_OPAQUE(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, void *ptr, intptr_t len, const char *format,
const char *descr);
struct sysctl_oid *
SYSCTL_ADD_PROC(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, void *arg1, intptr_t arg2,
int (*handler) (SYSCTL_HANDLER_ARGS), const char *format,
const char *descr);
struct sysctl_oid *
SYSCTL_ADD_QUAD(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, int64_t *ptr, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_ROOT_NODE(struct sysctl_ctx_list *ctx, int number,
const char *name, int ctlflags, int (*handler)(SYSCTL_HANDLER_ARGS),)(SYSCTL_HANDLER_ARGS),
const char *descr);
struct sysctl_oid *
SYSCTL_ADD_S8(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, int8_t *ptr, int8_t val, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_S16(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, int16_t *ptr, int16_t val, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_S32(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, int32_t *ptr, int32_t val, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_S64(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, int64_t *ptr, int64_t val, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_SBINTIME_MSEC(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, sbintime_t *ptr, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_SBINTIME_USEC(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, sbintime_t *ptr, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_STRING(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, char *ptr, intptr_t len, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_CONST_STRING(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, const char *ptr, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_STRUCT(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, void *ptr, struct_type, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_TIMEVAL_SEC(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, struct timeval *ptr, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_U8(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, uint8_t *ptr, uint8_t val, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_U16(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, uint16_t *ptr, uint16_t val, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_U32(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, uint32_t *ptr, uint32_t val, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_U64(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, uint64_t *ptr, uint64_t val, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_UINT(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, unsigned int *ptr, unsigned int val,
const char *descr);
struct sysctl_oid *
SYSCTL_ADD_ULONG(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, unsigned long *ptr, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_UQUAD(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, uint64_t *ptr, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_UMA_CUR(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, uma_zone_t ptr, const char *descr);
struct sysctl_oid *
SYSCTL_ADD_UMA_MAX(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, uma_zone_t ptr, const char *descr);
const char *descr
struct sysctl_oid *
SYSCTL_ADD_UAUTO(struct sysctl_ctx_list *ctx,
struct sysctl_oid_list *parent, int number, const char *name,
int ctlflags, void *ptr, const char *descr);
struct sysctl_oid_list *
SYSCTL_CHILDREN(struct sysctl_oid *oidp);
struct sysctl_oid_list *
SYSCTL_STATIC_CHILDREN(struct sysctl_oid_list OID_NAME);
struct sysctl_oid_list *
SYSCTL_NODE_CHILDREN(parent, name);
struct sysctl_oid *
SYSCTL_PARENT(struct sysctl_oid *oid);
SYSCTL_BOOL(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_COUNTER_U64(parent, number, name, ctlflags, ptr, descr);
SYSCTL_COUNTER_U64_ARRAY(parent, number, name, ctlflags, ptr, len,
descr);
SYSCTL_INT(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_INT_WITH_LABEL(parent, number, name, ctlflags, ptr, val, descr,
label);
SYSCTL_LONG(parent, number, name, ctlflags, ptr, val, descr);
int
sysctl_msec_to_ticks(SYSCTL_HANDLER_ARGS);
SYSCTL_NODE(parent, number, name, ctlflags, handler, descr);
SYSCTL_NODE_WITH_LABEL(parent, number, name, ctlflags, handler, descr,
label);
SYSCTL_OPAQUE(parent, number, name, ctlflags, ptr, len, format, descr);
SYSCTL_PROC(parent, number, name, ctlflags, arg1, arg2, handler, format,
descr);
SYSCTL_QUAD(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_ROOT_NODE(number, name, ctlflags, handler, descr);
SYSCTL_S8(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_S16(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_S32(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_S64(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_SBINTIME_MSEC(parent, number, name, ctlflags, ptr, descr);
SYSCTL_SBINTIME_USEC(parent, number, name, ctlflags, ptr, descr);
SYSCTL_STRING(parent, number, name, ctlflags, arg, len, descr);
SYSCTL_CONST_STRING(parent, number, name, ctlflags, arg, descr);
SYSCTL_STRUCT(parent, number, name, ctlflags, ptr, struct_type, descr);
SYSCTL_TIMEVAL_SEC(parent, number, name, ctlflags, ptr, descr);
SYSCTL_U8(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_U16(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_U32(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_U64(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_UINT(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_ULONG(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_UQUAD(parent, number, name, ctlflags, ptr, val, descr);
SYSCTL_UMA_MAX(parent, number, name, ctlflags, ptr, descr);
SYSCTL_UMA_CUR(parent, number, name, ctlflags, ptr, 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
ctx Pointer to sysctl context or NULL, if no context. See
sysctl_ctx_init(9) 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.
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
SYSCTL_STATIC_CHILDREN() macro for static sysctls and the
SYSCTL_CHILDREN() macro for dynamic sysctls. The
SYSCTL_PARENT() macro can be used to get the parent of an OID.
The macro returns NULL if there is no parent.
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.
name The name of the OID. The newly created OID will contain a copy
of the name.
ctlflags A bit mask of sysctl control flags. See the section below
describing all the control flags.
arg1 First callback argument for procedure sysctls.
arg2 Second callback argument for procedure sysctls.
len The length of the data pointed to by the 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.
For array type OIDs the length must be greater than zero.
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 val
argument.
val If the ptr argument is SYSCTL_NULL_XXX_PTR, gives the constant
value returned by this OID. Else this argument is not used.
struct_type
Name of structure type.
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 SYSCTL_PROC() macro or the SYSCTL_ADD_PROC()
function.
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
descr A pointer to a textual description of the OID.
label A pointer to an aggregation label for this component of the
OID. To make it easier to export sysctl data to monitoring
systems that support aggregations through labels (e.g.,
Prometheus), this argument can be used to attach a label name
to an OID. The label acts as a hint that this component's name
should not be part of the metric's name, but attached to the
metric as a label instead.
Labels should only be applied to siblings that are structurally
similar and encode the same type of value, as aggregation is of
no use otherwise.
NODE VALUE TYPES
Most of the macros and functions used to create sysctl nodes export a
read-only constant or in-kernel variable whose type matches the type of
the node's value. For example, SYSCTL_INT() reports the raw value of an
associated variable of type int. However, nodes may also export a value
that is a translatation of an internal representation.
The sysctl_msec_to_ticks() handler can be used with SYSCTL_PROC() or
SYSCTL_ADD_PROC() to export a millisecond time interval. When using this
handler, the arg2 parameter points to an in-kernel variable of type int
which stores a tick count suitable for use with functions like tsleep(9).
The sysctl_msec_to_ticks() function converts this value to milliseconds
when reporting the node's value. Similarly, sysctl_msec_to_ticks()
accepts new values in milliseconds and stores an equivalent value in
ticks to *arg2. Note that new code should use kernel variables of type
sbintime_t instead of tick counts.
The SYSCTL_ADD_SBINTIME_MSEC() and SYSCTL_ADD_SBINTIME_USEC() functions
and SYSCTL_SBINTIME_MSEC() and SYSCTL_SBINTIME_USEC() macros all create
nodes which export an in-kernel variable of type sbintime_t. These nodes
do not export the raw value of the associated variable. Instead, they
export a 64-bit integer containing a count of either milliseconds (the
MSEC variants) or microseconds (the USEC variants).
The SYSCTL_ADD_TIMEVAL_SEC() function and SYSCTL_TIMEVAL_SEC() macro
create nodes which export an in-kernel variable of type struct timeval.
These nodes do not export full value of the associated structure.
Instead, they export a count in seconds as a simple integer which is
stored in the tv_sec field of the associated variable. This function and
macro are intended to be used with variables which store a non-negative
interval rather than an absolute time. As a result, they reject attempts
to store negative values.
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 SYSCTL_ROOT_NODE() macro or the
SYSCTL_ADD_ROOT_NODE() function needs to be used. By default all static
sysctl node OIDs are global and need a SYSCTL_DECL() statement prior to
their SYSCTL_NODE() definition statement, typically in a so-called header
file.
CREATING SYSCTL STRINGS
Zero terminated character strings sysctls are created either using the
SYSCTL_STRING() macro or the SYSCTL_ADD_STRING() function. If the len
argument in zero, the string length is computed at every access to the
OID using strlen(3). Use the SYSCTL_CONST_STRING() macro or the
SYSCTL_ADD_CONST_STRING() function to add a sysctl for a constant string.
CREATING OPAQUE SYSCTLS
The SYSCTL_OPAQUE() or SYSCTL_STRUCT() macros or the SYSCTL_ADD_OPAQUE()
or SYSCTL_ADD_STRUCT() functions create an OID that handle any chunk of
data of the size specified by the len argument and data pointed to by the
ptr argument. When using the structure version the type is encoded as
part of the created sysctl.
CREATING CUSTOM SYSCTLS
The SYSCTL_PROC() macro and the 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 SYSCTL_BOOL(),
SYSCTL_COUNTER_U64(), SYSCTL_COUNTER_U64_ARRAY(), SYSCTL_INT(),
SYSCTL_INT_WITH_LABEL(), SYSCTL_LONG(), SYSCTL_NODE(),
SYSCTL_NODE_WITH_LABEL(), SYSCTL_OPAQUE(), SYSCTL_PROC(), SYSCTL_QUAD(),
SYSCTL_ROOT_NODE(), SYSCTL_S8(), SYSCTL_S16(), SYSCTL_S32(),
SYSCTL_S64(), SYSCTL_SBINTIME_MSEC(), SYSCTL_SBINTIME_USEC(),
SYSCTL_STRING(), SYSCTL_CONST_STRING(), SYSCTL_STRUCT(),
SYSCTL_TIMEVAL_SEC(), SYSCTL_U8(), SYSCTL_U16(), SYSCTL_U32(),
SYSCTL_U64(), SYSCTL_UINT(), SYSCTL_ULONG(), SYSCTL_UQUAD(),
SYSCTL_UMA_CUR() or SYSCTL_UMA_MAX() macros.
CREATING A DYNAMIC SYSCTL
Dynamic nodes are created using one of the SYSCTL_ADD_BOOL(),
SYSCTL_ADD_COUNTER_U64(), SYSCTL_ADD_COUNTER_U64_ARRAY(),
SYSCTL_ADD_INT(), SYSCTL_ADD_LONG(), SYSCTL_ADD_NODE(),
SYSCTL_ADD_NODE_WITH_LABEL(), 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_SBINTIME_MSEC(), SYSCTL_ADD_SBINTIME_USEC(),
SYSCTL_ADD_STRING(), SYSCTL_ADD_CONST_STRING(), SYSCTL_ADD_STRUCT(),
SYSCTL_ADD_TIMEVAL_SEC(), 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_ADD_UMA_CUR() or SYSCTL_ADD_UMA_MAX() functions. See
sysctl_remove_oid(9) or sysctl_ctx_free(9) 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 -- 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.
CTLFLAG_MPSAFE This sysctl(9) handler is MP safe. Do not grab
Giant around calls to this handler. This should
only be used for SYSCTL_PROC() entries.
Additionally, any of the following optional flags may also be specified:
CTLFLAG_ANYBODY Any user or process can write to this sysctl.
CTLFLAG_CAPRD A process in capability mode can read from this
sysctl.
CTLFLAG_CAPWR A process in capability mode 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 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), device_get_sysctl(9), sysctl_add_oid(9),
sysctl_ctx_free(9), sysctl_ctx_init(9), sysctl_remove_oid(9)
HISTORY
The sysctl(8) utility first appeared in 4.4BSD.
AUTHORS
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.
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.
FreeBSD 13.1-RELEASE-p6 September 1, 2020 FreeBSD 13.1-RELEASE-p6
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