int
sysctl(
const int *name
, u_int namelen
, void *oldp
, size_t *oldlenp
, const void *newp
, size_t newlen
)
int
sysctlbyname(
const char *sname
, void *oldp
, size_t *oldlenp
, void *newp
, size_t newlen
)
int
sysctlgetmibinfo(
const char *sname
, int *name
, u_int *namelenp
, char *cname
, size_t *csz
, struct sysctlnode **rnode
, int v
)
int
sysctlnametomib(
const char *sname
, int *name
, size_t *namelenp
)
Unless explicitly noted below, sysctl returns a consistent snapshot of the data requested. Consistency is obtained by locking the destination buffer into memory so that the data may be copied out without blocking. Calls to sysctl are serialized to avoid deadlock.
The state is described using a ``Management Information Base'' (MIB)
style name, listed in
name
,
which is a
namelen
length array of integers.
The
sysctlbyname()
function accepts a string representation of a MIB entry and internally
maps it to the appropriate numeric MIB representation.
Its semantics are otherwise no different from
sysctl(
).
The information is copied into the buffer specified by
oldp
.
The size of the buffer is given by the location specified by
oldlenp
before the call,
and that location gives the amount of data copied after a successful call.
If the amount of data available is greater
than the size of the buffer supplied,
the call supplies as much data as fits in the buffer provided
and returns with the error code ENOMEM.
If the old value is not desired,
oldp
and
oldlenp
should be set to
NULL
.
The size of the available data can be determined by calling
sysctl
with a
NULL
parameter for
oldp
.
The size of the available data will be returned in the location pointed to by
oldlenp
.
For some operations, the amount of space may change often.
For these operations,
the system attempts to round up so that the returned size is
large enough for a call to return the data shortly thereafter.
To set a new value,
newp
is set to point to a buffer of length
newlen
from which the requested value is to be taken.
If a new value is not to be set,
newp
should be set to
NULL
and
newlen
set to 0.
The
sysctlnametomib()
function can be used to map the string representation of a MIB entry
to the numeric version.
The
name
argument should point to an array of integers large enough to hold the
MIB, and
namelenp
should indicate the number of integer slots available.
Following a successful translation, the size_t indicated by
namelenp
will be changed to show the number of slots consumed.
The
sysctlgetmibinfo()
function performs name translation similar to
sysctlnametomib(
),
but also canonicalizes the name (or returns the first erroneous token
from the string being parsed) into the space indicated by
cname
and
csz
.
csz
should indicate the size of the buffer pointed to by
cname
and on return, will indicate the size of the returned string including
the trailing
`nul'
character.
The
rnode
and
v
arguments to
sysctlgetmibinfo()
are used to provide a tree for it to parse into, and to get back
either a pointer to, or a copy of, the terminal node.
If
rnode
is
NULL
,
sysctlgetmibinfo()
uses its own internal tree for parsing, and checks it against the
kernel at each call, to make sure that the name-to-number mapping is
kept up to date.
The
v
argument is ignored in this case.
If
rnode
is not
NULL
but the pointer it references is, on a successful return,
rnode
will be adjusted to point to a copy of the terminal node.
The
v
argument indicates which version of the
sysctl
node structure the caller wants.
The application must later
free()
this copy.
If neither
rnode
nor the pointer it references are
NULL
,
the pointer is used as the address of a tree over which the parsing is
done.
In this last case, the tree is not checked against the kernel, no
refreshing of the mappings is performed, and the value given by
v
must agree with the version indicated by the tree.
It is recommended that applications always use
SYSCTL_VERSION
as the value for
v
,
as defined in the include file
sys/sysctl.h
.
The numeric and text names of sysctl variables are described in
sysctl(7).
The numeric names are defined as preprocessor macros.
The top level names are defined with a CTL_ prefix in
<sys/sysctl.h
>.
The next and subsequent levels down have different prefixes for each
subtree.
For example, the following retrieves the maximum number of processes allowed
in the system - the
kern.maxproc
variable:
int mib[2], maxproc;
size_t len;
mib[0] = CTL_KERN;
mib[1] = KERN_MAXPROC;
len = sizeof(maxproc);
sysctl(mib, 2, &maxproc, &len, NULL, 0);
user.cs_path
:
int mib[2];
size_t len;
char *p;
mib[0] = CTL_USER;
mib[1] = USER_CS_PATH;
sysctl(mib, 2, NULL, &len, NULL, 0);
p = malloc(len);
sysctl(mib, 2, p, &len, NULL, 0);
Name Description |
CTL_QUERY Retrieve a mapping of names to numbers below a given node |
CTL_CREATE Create a new node |
CTL_CREATESYM Create a new node by its kernel symbol |
CTL_DESTROY Destroy a node |
CTL_DESCRIBE Retrieve node descriptions |
The core interface to all of these meta-functions is the structure
that the kernel uses to describe the tree internally, as defined in
<sys/sysctl.h
>
as:
#define sysctl_csize sysctl_un.scu_child.suc_csize
#define sysctl_clen sysctl_un.scu_child.suc_clen
#define sysctl_child sysctl_un.scu_child.suc_child
#define sysctl_data sysctl_un.scu_data.sud_data
#define sysctl_offset sysctl_un.scu_data.sud_offset
#define sysctl_alias sysctl_un.scu_alias
#define sysctl_idata sysctl_un.scu_idata
#define sysctl_qdata sysctl_un.scu_qdata
struct sysctlnode {
uint32_t sysctl_flags; /* flags and type */
int32_t sysctl_num; /* mib number */
char sysctl_name[SYSCTL_NAMELEN]; /* node name */
uint32_t sysctl_ver; /* node's version vs. rest of tree */
uint32_t __rsvd;
union {
struct {
uint32_t suc_csize; /* size of child node array */
uint32_t suc_clen; /* number of valid children */
struct sysctlnode* suc_child; /* array of child nodes */
} scu_child;
struct {
void *sud_data; /* pointer to external data */
size_t sud_offset; /* offset to data */
} scu_data;
int32_t scu_alias; /* node this node refers to */
int32_t scu_idata; /* immediate "int" data */
u_quad_t scu_qdata; /* immediate "u_quad_t" data */
} sysctl_un;
size_t _sysctl_size; /* size of instrumented data */
sysctlfn _sysctl_func; /* access helper function */
struct sysctlnode *sysctl_parent; /* parent of this node */
const char *sysctl_desc; /* description of node */
};
Querying the tree to discover the name to number mapping permits dynamic discovery of all the data that the tree currently has instrumented. For example, to discover all the nodes below the CTL_VFS node:
struct sysctlnode query, vfs[128];
int mib[2];
size_t len;
mib[0] = CTL_VFS;
mib[1] = CTL_QUERY;
memset(&query, 0, sizeof(query));
query.sysctl_flags = SYSCTL_VERSION;
len = sizeof(vfs);
sysctl(mib, 2, &vfs[0], &len, &query, sizeof(query));
Note that a reference to an empty node with
sysctl_flags
set to
SYSCTL_VERSION
is passed to sysctl in order to indicate the version that the program
is using.
All dynamic operations passing nodes into sysctl require that the
version be explicitly specified.
Creation and destruction of nodes works by constructing part of a new
node description (or a description of the existing node) and invoking
CTL_CREATE (or CTL_CREATESYM) or CTL_DESTROY at the parent of the new
node, with a pointer to the new node passed via the
new
and
newlen
arguments.
If valid values for
old
and
oldlenp
are passed, a copy of the new node once in the tree will be returned.
If the create operation fails because a node with the same name or MIB
number exists, a copy of the conflicting node will be returned.
The minimum requirements for creating a node are setting the
sysctl_flags
to indicate the new node's type,
sysctl_num
to either the new node's number (or CTL_CREATE or CTL_CREATESYM if a
dynamically allocated MIB number is acceptable),
sysctl_size
to the size of the data to be instrumented (which must agree with the
given type), and
sysctl_name
must be set to the new node's name.
Nodes that are not of type
``node''
must also have some description of the data to be instrumented, which
will vary depending on what is to be instrumented.
If existing kernel data is to be covered by this new node, its address
should be given in
sysctl_data
or, if CTL_CREATESYM is used,
sysctl_data
should be set to a string containing its name from the kernel's symbol
table.
If new data is to be instrumented and an initial value is available,
the new integer or quad type data should be placed into either
sysctl_idata
or
sysctl_qdata
,
respectively, along with the SYSCTL_IMMEDIATE flag being set, or
sysctl_data
should be set to point to a copy of the new data, and the
SYSCTL_OWNDATA flag must be set.
This latter method is the only way that new string and struct type
nodes can be initialized.
Invalid kernel addresses are accepted, but any attempt to access those
nodes will return an error.
The
sysctl_csize
,
sysctl_clen
,
sysctl_child
,
sysctl_parent
,
and
sysctl_alias
members are used by the kernel to link the tree together and must be
NULL
or 0.
Nodes created in this manner cannot have helper functions, so
sysctl_func
must also be
NULL
.
If the
sysctl_ver
member is non-zero, it must match either the version of the parent or
the version at the root of the MIB or an error is returned.
This can be used to ensure that nodes are only added or removed from a
known state of the tree.
Note: It may not be possible to determine the version at the root
of the tree.
This example creates a new subtree and adds a node to it that controls the
audiodebug
kernel variable, thereby making it tunable at at any time, without
needing to use
ddb(4)
or
kvm(3)
to alter the kernel's memory directly.
struct sysctlnode node;
int mib[2];
size_t len;
mib[0] = CTL_CREATE; /* create at top-level */
len = sizeof(node);
memset(&node, 0, len);
node.sysctl_flags = SYSCTL_VERSION|CTLFLAG_READWRITE|CTLTYPE_NODE;
snprintf(node.sysctl_name, sizeof(node.sysctl_name), "local");
node.sysctl_num = CTL_CREATE; /* request dynamic MIB number */
sysctl(&mib[0], 1, &node, &len, &node, len);
mib[0] = node.sysctl_num; /* use new MIB number */
mib[1] = CTL_CREATESYM; /* create at second level */
len = sizeof(node);
memset(&node, 0, len);
node.sysctl_flags = SYSCTL_VERSION|CTLFLAG_READWRITE|CTLTYPE_INT;
snprintf(node.sysctl_name, sizeof(node.sysctl_name), "audiodebug");
node.sysctl_num = CTL_CREATE;
node.sysctl_data = "audiodebug"; /* kernel symbol to be used */
sysctl(&mib[0], 2, NULL, NULL, &node, len);
The process for deleting nodes is similar, but less data needs to
be supplied.
Only the
sysctl_num
field
needs to be filled in; almost all other fields must be left blank.
The
sysctl_name
and/or
sysctl_ver
fields can be filled in with the name and version of the existing node
as additional checks on what will be deleted.
If all the given data fail to match any node, nothing will be deleted.
If valid values for
old
and
oldlenp
are supplied and a node is deleted, a copy of what was in the MIB tree
will be returned.
This sample code shows the deletion of the two nodes created in the above example:
int mib[2];
len = sizeof(node);
memset(&node, 0, len);
node.sysctl_flags = SYSCTL_VERSION;
mib[0] = 3214; /* assumed number for "local" */
mib[1] = CTL_DESTROY;
node.sysctl_num = 3215; /* assumed number for "audiodebug" */
sysctl(&mib[0], 2, NULL, NULL, &node, len);
mib[0] = CTL_DESTROY;
node.sysctl_num = 3214; /* now deleting "local" */
sysctl(&mib[0], 1, NULL, NULL, &node, len);
Descriptions of each of the nodes can also be retrieved, if they are
available.
Descriptions can be retrieved in bulk at each level or on a per-node
basis.
The layout of the buffer into which the descriptions are returned is a
series of variable length structures, each of which describes its own
size.
The length indicated includes the terminating
`nul'
character.
Nodes that have no description or where the description is not
available are indicated by an empty string.
The
descr_ver
will match the
sysctl_ver
value for a given node, so that descriptions for nodes whose number
have been recycled can be detected and ignored or discarded.
struct sysctldesc {
int32_t descr_num; /* mib number of node */
uint32_t descr_ver; /* version of node */
uint32_t descr_len; /* length of description string */
char descr_str[1]; /* not really 1...see above */
};
The
NEXT_DESCR()
macro can be used to skip to the next description in the retrieved
list.
struct sysctlnode desc;
struct sysctldesc *d;
char buf[1024];
int mib[2];
size_t len;
/* retrieve kern-level descriptions */
mib[0] = CTL_KERN;
mib[1] = CTL_DESCRIBE;
d = (struct sysctldesc *)&buf[0];
len = sizeof(buf);
sysctl(mib, 2, d, &len, NULL, 0);
while ((caddr_t)d < (caddr_t)&buf[len]) {
printf("node %d: %.*s\n", d->descr_num, d->descr_len,
d->descr_str);
d = NEXT_DESCR(d);
}
/* retrieve description for kern.securelevel */
memset(&desc, 0, sizeof(desc));
desc.sysctl_flags = SYSCTL_VERSION;
desc.sysctl_num = KERN_SECURELEVEL;
d = (struct sysctldesc *)&buf[0];
len = sizeof(buf);
sysctl(mib, 2, d, &len, &desc, sizeof(desc));
printf("kern.securelevel: %.*s\n", d->descr_len, d->descr_str);
Descriptions can also be set as follows, subject to the following rules:
struct sysctlnode desc;
int mib[2];
/* presuming the given top-level node was just added... */
mib[0] = 3214; /* mib numbers taken from previous examples */
mib[1] = CTL_DESCRIBE;
memset(&desc, 0, sizeof(desc));
desc.sysctl_flags = SYSCTL_VERSION;
desc.sysctl_num = 3215;
desc.sysctl_desc = "audio debug control knob";
sysctl(mib, 2, NULL, NULL, &desc, sizeof(desc));
Upon successfully setting a description, the new description will be
returned in the space indicated by the
oldp
and
oldlenp
arguments.
The
sysctl_flags
field in the struct sysctlnode contains the sysctl version, node type
information, and a number of flags.
The macros
SYSCTL_VERS(),
SYSCTL_TYPE(
),
and
SYSCTL_FLAGS(
)
can be used to access the different fields.
Valid flags are:
Name Description |
CTLFLAG_READONLY Node is read-only |
CTLFLAG_READONLY1 Node becomes read-only at securelevel 1 |
CTLFLAG_READONLY2 Node becomes read-only at securelevel 2 |
CTLFLAG_READWRITE Node is writable by the superuser |
CTLFLAG_ANYWRITE Node is writable by anyone |
CTLFLAG_PRIVATE Node is readable only by the superuser |
CTLFLAG_PERMANENT Node cannot be removed (cannot be set by processes) |
CTLFLAG_OWNDATA Node owns data and does not instrument existing data |
CTLFLAG_IMMEDIATE Node contains instrumented data and does not instrument existing data |
CTLFLAG_HEX Node's contents should be displayed in a hexadecimal form |
CTLFLAG_ROOT Node is the root of a tree (cannot be set at any time) |
CTLFLAG_ANYNUMBER Node matches any MIB number (cannot be set by processes) |
CTLFLAG_HIDDEN Node not displayed by default |
CTLFLAG_ALIAS Node refers to a sibling node (cannot be set by processes) |
CTLFLAG_OWNDESC Node owns its own description string space |
sys/sysctl.h
>
sys/socket.h
>
sys/gmon.h
>
uvm/uvm_param.h
>
netinet/in.h
>
netinet/icmp_var.h
>
netinet/icmp6.h
>
netinet/tcp_var.h
>
netinet/udp_var.h
>
netinet6/udp6_var.h
>
netinet6/ipsec.h
>
netkey/key_var.h
>
machine/cpu.h
>
EFAULT
]
name
,
oldp
,
newp
,
or length pointer
oldlenp
contains an invalid address, or the requested value is temporarily
unavailable.
EINVAL
]
name
array is zero or greater than CTL_MAXNAME.
EINVAL
]
newp
is given and its specified length in
newlen
is too large or too small, or the given value is not acceptable for
the given node.
EISDIR
]
name
array specifies an intermediate rather than terminal name.
ENOENT
]
name
array specifies a node that does not exist in the tree.
ENOENT
]
ENOMEM
]
oldlenp
is too short to hold the requested value.
ENOTDIR
]
name
array specifies a node below a node that addresses data.
ENOTEMPTY
]
EOPNOTSUPP
]
name
array specifies a value that is unknown or a meta-operation was
attempted that the requested node does not support.
EPERM
]
EPERM
]
EPERM
]