sysctl_add_oidsysctl_move_oidsysctl_remove_oid
- runtime sysctl tree manipulation
SYNOPSIS
#include <sys/types.h>
#include <sys/sysctl.h> struct sysctl_oid *
Fo sysctl_add_oid
Fa struct sysctl_ctx_list *ctx
Fa struct sysctl_oid_list *parent
Fa int number
Fa const char *name
Fa int kind
Fa void *arg1
Fa int arg2
Fa int (*handler) (SYSCTL_HANDLER_ARGS)
Fa const char *format
Fa const char *descr
Fc Ft int
Fo sysctl_move_oid
Fa struct sysctl_oid *oidp
Fa struct sysctl_oid_list *parent
Fc Ft int
Fo sysctl_remove_oid
Fa struct sysctl_oid *oidp
Fa int del
Fa int recurse
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 *
Fo SYSCTL_ADD_OID
Fa struct sysctl_ctx_list *ctx
Fa struct sysctl_oid_list *parent
Fa int number
Fa const char *name
Fa int kind
Fa void *arg1
Fa int arg2
Fa int (*handler) (SYSCTL_HANDLER_ARGS)
Fa const char *format
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 access
Fa int (*handler) (SYSCTL_HANDLER_ARGS)
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 access
Fa char *arg
Fa int len
Fa const char *descr
Fc 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 access
Fa int *arg
Fa int len
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 access
Fa unsigned int *arg
Fa int len
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 access
Fa long *arg
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 access
Fa unsigned long *arg
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 access
Fa void *arg
Fa int len
Fa const char *format
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 access
Fa void *arg
Fa STRUCT_NAME
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 access
Fa void *arg1
Fa int arg2
Fa int (*handler) (SYSCTL_HANDLER_ARGS)
Fa const char *format
Fa const char *descr
Fc
DESCRIPTION
These functions and macros provide an interface
for creating and deleting sysctl oids at runtime
(e.g. during lifetime of a module).
The alternative method,
based on linker sets (see
#include <sys/linker_set.h>
and
src/sys/kern/kern_sysctl.c
for details), only allows creation and deletion
on module load and unload respectively.
Dynamic oids of type
CTLTYPE_NODE
are reusable
so that several code sections can create and delete them,
but in reality they are allocated and freed
based on their reference count.
As a consequence,
it is possible for two or more code sections
to create partially overlapping trees that they both can use.
It is not possible to create overlapping leaves,
nor to create different child types with the same name and parent.
Newly created oids are connected to their parent nodes.
In all these functions and macros
(with the exception of
sysctl_remove_oid () ,);
one of the required parameters is
Fa parent ,
which points to the head of the parent's list of children.
Most top level categories are created statically.
When connecting to existing static oids,
this pointer can be obtained with the
SYSCTL_STATIC_CHILDREN ();
macro, where the
Fa OID_NAME
argument is name of the parent oid of type
CTLTYPE_NODE
(i.e., the name displayed by
sysctl(8),
preceded by underscore, and with all dots replaced with underscores).
When connecting to an existing dynamic oid, this pointer
can be obtained with the
SYSCTL_CHILDREN ();
macro, where the
Fa oidp
argument points to the parent oid of type
CTLTYPE_NODE
The
sysctl_add_oid ();
function creates raw oids of any type.
If the oid is successfully created,
the function returns a pointer to it;
otherwise it returns
NULL
Many of the arguments for
sysctl_add_oid ();
are common to the macros.
The arguments are as follows:
Fa ctx
A pointer to an optional sysctl context, or
NULL
See
sysctl_ctx_init9
for details.
Programmers are strongly advised to use contexts
to organize the dynamic oids which they create,
unless special creation and deletion sequences are required.
If
Fa ctx
is not
NULL
the newly created oid will be added to this context
as its first entry.
Fa parent
A pointer to a
struct sysctl_oid_list
which is the head of the parent's list of children.
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 kind
The kind of oid,
specified as a bit mask of the type and access values defined in the
#include <sys/sysctl.h>
header file.
Oids created dynamically always have the
CTLFLAG_DYN
flag set.
Access flags specify whether this oid is read-only or read-write,
and whether it may be modified by all users
or by the superuser only.
Fa arg1
A pointer to any data that the oid should reference, or
NULL
Fa arg2
The size of
Fa arg1 ,
or 0 if
Fa arg1
is
NULL
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 also to define new handlers using the
SYSCTL_ADD_PROC ();
macro.
Fa format
A pointer to a string
which specifies the format of the oid symbolically.
This format is used as a hint by
sysctl(8)
to apply proper data formatting for display purposes.
Currently used format names are:
``N''
for node,
``A''
for
char *
``I''
for
int
``IU''
for
unsigned int
``L''
for
long
``LU''
for
unsigned long
and
``S,TYPE''
for
struct TYPE
structures.
Fa descr
A pointer to a textual description of the oid.
The
sysctl_move_oid ();
function reparents an existing oid.
The oid is assigned a new number as if it had been created with
Fa number
set to
OID_AUTO
The
sysctl_remove_oid ();
function removes a dynamically created oid from the tree,
optionally freeing its resources.
It takes the following arguments:
Fa oidp
A pointer to the dynamic oid to be removed.
If the oid is not dynamic, or the pointer is
NULL
the function returns
Er EINVAL .
Fa del
If non-zero,
sysctl_remove_oid ();
will try to free the oid's resources
when the reference count of the oid becomes zero.
However, if
Fa del
is set to 0,
the routine will only deregister the oid from the tree,
without freeing its resources.
This behaviour is useful when the caller expects to rollback
(possibly partially failed)
deletion of many oids later.
Fa recurse
If non-zero, attempt to remove the node and all its children.
If
recurse
is set to 0,
any attempt to remove a node that contains any children
will result in a
Er ENOTEMPTY
error.
WARNING : use recursive deletion with extreme caution
Normally it should not be needed if contexts are used.
Contexts take care of tracking inter-dependencies
between users of the tree.
However, in some extreme cases it might be necessary
to remove part of the subtree no matter how it was created,
in order to free some other resources.
Be aware, though, that this may result in a system
panic(9)
if other code sections continue to use removed subtrees.
Again, in most cases the programmer should use contexts,
as described in
sysctl_ctx_init9,
to keep track of created oids,
and to delete them later in orderly fashion.
There is a set of macros defined
that helps to create oids of given type.
They are as follows:
Fn SYSCTL_ADD_OID
creates a raw oid.
This macro is functionally equivalent to the
sysctl_add_oid ();
function.
Fn SYSCTL_ADD_NODE
creates an oid of type
CTLTYPE_NODE
to which child oids may be added.
Fn SYSCTL_ADD_STRING
creates an oid that handles a zero-terminated character string.
Fn SYSCTL_ADD_INT
creates an oid that handles an
int
variable.
Fn SYSCTL_ADD_UINT
creates an oid that handles an
unsigned int
variable.
Fn SYSCTL_ADD_LONG
creates an oid that handles a
long
variable.
Fn SYSCTL_ADD_ULONG
creates an oid that handles an
unsigned long
variable.
Fn SYSCTL_ADD_OPAQUE
creates an oid that handles any chunk of opaque data
of the size specified by the
Fa len
argument,
which is a pointer to a
size_t *
Fn SYSCTL_ADD_STRUCT
creates an oid that handles a
struct TYPE
structure.
The
Fa format
parameter will be set to
``S,TYPE''
to provide proper hints to the
sysctl(8)
utility.
Fn SYSCTL_ADD_PROC
creates an oid with the specified
handler
function.
The handler is responsible for handling 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.
EXAMPLES
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.
*/
struct sysctl_oid *root1, *root2, *oidp;
int a_int;
char *string = "dynamic sysctl";
...
root1 = SYSCTL_ADD_NODE( NULL, SYSCTL_STATIC_CHILDREN(/* tree top */),
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!
Sharing nodes between many code sections
causes interdependencies that sometimes may lock the resources.
For example,
if module A hooks up a subtree to an oid created by module B,
module B will be unable to delete that oid.
These issues are handled properly by sysctl contexts.
Many operations on the tree involve traversing linked lists.
For this reason, oid creation and removal is relatively costly.
