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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_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 alterna‐
tive 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 sec‐
tions 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 par‐
ent’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 under‐
scores).
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 #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.
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 han‐
dlers 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 sym‐
bolically. 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 argu‐
ments:
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 (possi‐
bly 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 con‐
tains 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 char‐
acter string.
SYSCTL_ADD_INT() creates an oid that handles an int variable.
SYSCTL_ADD_UINT() creates an oid that handles an unsigned int vari‐
able.
SYSCTL_ADD_LONG() creates an oid that handles a long variable.
SYSCTL_ADD_ULONG() creates an oid that handles an unsigned long vari‐
able.
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 pro‐
vide 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 espe‐
cially useful if the kernel data is not easily
accessible, or needs to be processed before export‐
ing.
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 inter‐
mediate 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!
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.