|SYSCTL_ADD_OID(9)||Kernel Developer's Manual||SYSCTL_ADD_OID(9)|
struct sysctl_oid *
*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);
*oidp, struct sysctl_oid_list *parent);
*oidp, int del, int
*oidp, const char *name, int
del, int recurse);
DESCRIPTION¶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
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.
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
NULL. Many of the arguments for
sysctl_add_oid() are common to the wrapper macros
defined by sysctl(9).
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
sysctl_remove_oid() function removes a
dynamically created OID from the tree and optionally freeing its resources.
It takes the following arguments:
- A pointer to the dynamic OID to be removed. If the OID is not dynamic, or
the pointer is
NULL, the function returns
- 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.
- 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
ENOTEMPTYerror. 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.
sysctl_remove_name() function looks up
the child node matching the name argument and then
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
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.
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.
|November 6, 2015||Linux 4.9.0-9-amd64|