sysctl_add_oid, sysctl_move_oid, sysctl_remove_oid, sysctl_remove_name — runtime sysctl tree manipulation

       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.

Debian                                          December 13, 2016                              SYSCTL_ADD_OID(9)

       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:

       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:
                userecursivedeletionwithextremecaution!  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.

       These functions first appeared in FreeBSD 4.2.

       sysctl_add_oid, sysctl_move_oid, sysctl_remove_oid, sysctl_remove_name — runtime sysctl tree manipulation

sysctl(8), sysctl(9), sysctl_ctx_free(9), sysctl_ctx_init(9)

#include<sys/types.h>#include<sys/sysctl.h>structsysctl_oid*sysctl_add_oid(structsysctl_ctx_list*ctx, structsysctl_oid_list*parent, intnumber, constchar*name,
           intkind,   void*arg1,   intmax_targ2,   int(*handler)(SYSCTL_HANDLER_ARGS),  constchar*format,
           constchar*descr, constchar*label);

       intsysctl_move_oid(structsysctl_oid*oidp, structsysctl_oid_list*parent);

       intsysctl_remove_oid(structsysctl_oid*oidp, intdel, intrecurse);

       intsysctl_remove_name(structsysctl_oid*oidp, constchar*name, intdel, intrecurse);