NAME¶
sysctl_add_oid
,
sysctl_move_oid
,
sysctl_remove_oid
—
runtime sysctl tree manipulation
SYNOPSIS¶
#include
<sys/types.h>
#include
<sys/sysctl.h>
struct sysctl_oid *
sysctl_add_oid
(
struct
sysctl_ctx_list *ctx,
struct sysctl_oid_list
*parent,
int number,
const char *name,
int kind,
void
*arg1,
int arg2,
int (*handler) (SYSCTL_HANDLER_ARGS),
const char *format,
const char *descr);
int
sysctl_move_oid
(
struct
sysctl_oid *oidp,
struct sysctl_oid_list
*parent);
int
sysctl_remove_oid
(
struct
sysctl_oid *oidp,
int del,
int recurse);
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 *
SYSCTL_ADD_OID
(
struct
sysctl_ctx_list *ctx,
struct sysctl_oid_list
*parent,
int number,
const char *name,
int kind,
void
*arg1,
int arg2,
int (*handler) (SYSCTL_HANDLER_ARGS),
const char *format,
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 access,
int
(*handler) (SYSCTL_HANDLER_ARGS),
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 access,
char
*arg,
int 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 access,
int
*arg,
int len,
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 access,
unsigned int *arg,
int len,
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 access,
long
*arg,
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 access,
unsigned long *arg,
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 access,
int64_t *arg,
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 access,
uint64_t *arg,
const char *descr);
struct sysctl_oid *
SYSCTL_ADD_OPAQUE
(
struct
sysctl_ctx_list *ctx,
struct sysctl_oid_list
*parent,
int number,
const char *name,
int access,
void
*arg,
int len,
const char *format,
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 access,
void
*arg,
STRUCT_NAME,
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 access,
void
*arg1,
int arg2,
int (*handler) (SYSCTL_HANDLER_ARGS),
const char *format,
const char *descr);
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
<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
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
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
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:
- ctx
- A pointer to an optional sysctl context, or
NULL
. See
sysctl_ctx_init(9) 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 ctx is not
NULL
, the newly created oid will be
added to this context as its first entry.
- parent
- A pointer to a
struct sysctl_oid_list
, which is
the head of the parent's list of children.
- 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.
- kind
- The kind of oid, specified as a bit mask of the type and access values
defined in the
<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.
- arg1
- A pointer to any data that the oid should reference, or
NULL
.
- arg2
- The size of arg1, or 0 if
arg1 is
NULL
.
- 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.
- 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.
- 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
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:
- oidp
- A pointer to the dynamic oid to be removed. If the oid is not dynamic, or
the pointer is
NULL
, the function
returns EINVAL
.
- 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 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.
- 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
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_init(9), 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:
SYSCTL_ADD_OID
()
- creates a raw oid. This macro is functionally equivalent to the
sysctl_add_oid
() function.
SYSCTL_ADD_NODE
()
- creates an oid of type
CTLTYPE_NODE
, to
which child oids may be added.
SYSCTL_ADD_STRING
()
- creates an oid that handles a zero-terminated character string.
SYSCTL_ADD_INT
()
- creates an oid that handles an
int
variable.
SYSCTL_ADD_UINT
()
- creates an oid that handles an
unsigned int
variable.
SYSCTL_ADD_LONG
()
- creates an oid that handles a
long
variable.
SYSCTL_ADD_ULONG
()
- creates an oid that handles an
unsigned long
variable.
SYSCTL_ADD_QUAD
()
- creates an oid that handles an
int64_t
variable.
SYSCTL_ADD_OPAQUE
()
- creates an oid that handles any chunk of opaque data of the size specified
by the len argument, which is a pointer
to a
size_t *
.
SYSCTL_ADD_STRUCT
()
- creates an oid that handles a
struct TYPE
structure. The format parameter will be
set to “S,TYPE” to provide proper hints to the
sysctl(8) utility.
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!
SEE ALSO¶
sysctl(8),
sysctl(9),
sysctl_ctx_free(9),
sysctl_ctx_init(9)
HISTORY¶
These functions first appeared in
FreeBSD 4.2.
AUTHORS¶
Andrzej Bialecki
⟨abial@FreeBSD.org⟩
BUGS¶
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.