| SYSCTL_ADD_OID(9) | Kernel Developer's Manual | SYSCTL_ADD_OID(9) |
sysctl_add_oid,
sysctl_move_oid,
sysctl_remove_oid,
sysctl_remove_name — runtime
sysctl tree manipulation
#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,
intmax_t arg2, int (*handler)
(SYSCTL_HANDLER_ARGS), const char *format,
const char *descr, const char
*label);
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);
int
sysctl_remove_name(struct sysctl_oid
*oidp, const char *name, int
del, int recurse);
These functions provide the interface for creating and deleting
sysctl OIDs at runtime for example during the lifetime of a module. The
wrapper macros defined by sysctl(9) are recommended when
creating new OIDs.
sysctl_add_oid()
should not be called directly from the code.
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.
The
sysctl_add_oid()
function creates a raw OID of any type and connects it to its parent node,
if any. If the OID is successfully created, the function returns a pointer
to it else it returns NULL. Many of the arguments
for sysctl_add_oid() are common to the wrapper
macros defined by sysctl(9).
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 and optionally
freeing its resources. It takes the following arguments:
NULL, the function returns
EINVAL.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.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.The
sysctl_remove_name()
function looks up the child node matching the name
argument and then invokes the sysctl_remove_oid()
function on that node, passing along the del and
recurse arguments. If a node having the specified name
does not exist an error code of ENOENT is returned.
Else the error code from sysctl_remove_oid() is
returned.
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.
sysctl(8), sysctl(9), sysctl_ctx_free(9), sysctl_ctx_init(9)
These functions first appeared in FreeBSD 4.2.
Andrzej Bialecki <abial@FreeBSD.org>
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.
| December 13, 2016 | Debian |