203 lines
6.0 KiB
Groff
203 lines
6.0 KiB
Groff
.\"
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.\" Copyright (c) 2000, Andrzej Bialecki <abial@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd November 6, 2015
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.Dt SYSCTL_ADD_OID 9
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.Os
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.Sh NAME
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.Nm sysctl_add_oid ,
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.Nm sysctl_move_oid ,
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.Nm sysctl_remove_oid ,
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.Nm sysctl_remove_name
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.Nd runtime sysctl tree manipulation
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/sysctl.h
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.Ft struct sysctl_oid *
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.Fo sysctl_add_oid
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.Fa "struct sysctl_ctx_list *ctx"
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.Fa "struct sysctl_oid_list *parent"
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.Fa "int number"
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.Fa "const char *name"
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.Fa "int kind"
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.Fa "void *arg1"
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.Fa "intmax_t arg2"
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.Fa "int (*handler) (SYSCTL_HANDLER_ARGS)"
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.Fa "const char *format"
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.Fa "const char *descr"
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.Fc
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.Ft int
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.Fo sysctl_move_oid
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.Fa "struct sysctl_oid *oidp"
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.Fa "struct sysctl_oid_list *parent"
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.Fc
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.Ft int
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.Fo sysctl_remove_oid
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.Fa "struct sysctl_oid *oidp"
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.Fa "int del"
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.Fa "int recurse"
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.Fc
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.Ft int
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.Fo sysctl_remove_name
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.Fa "struct sysctl_oid *oidp"
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.Fa "const char *name"
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.Fa "int del"
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.Fa "int recurse"
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.Fc
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.Sh DESCRIPTION
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These functions provide the interface for creating and deleting sysctl
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OIDs at runtime for example during the lifetime of a module.
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The wrapper macros defined by
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.Xr sysctl 9
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are recommended when creating new OIDs.
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.Fn sysctl_add_oid
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should not be called directly from the code.
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.Pp
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Dynamic OIDs of type
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.Dv CTLTYPE_NODE
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are reusable
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so that several code sections can create and delete them,
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but in reality they are allocated and freed
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based on their reference count.
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As a consequence,
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it is possible for two or more code sections
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to create partially overlapping trees that they both can use.
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It is not possible to create overlapping leaves,
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nor to create different child types with the same name and parent.
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.Pp
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The
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.Fn sysctl_add_oid
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function creates a raw OID of any type and connects it to its parent node, if any.
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If the OID is successfully created,
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the function returns a pointer to it else
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it returns
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.Dv NULL .
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Many of the arguments for
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.Fn sysctl_add_oid
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are common to the wrapper macros defined by
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.Xr sysctl 9 .
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.Pp
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The
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.Fn sysctl_move_oid
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function reparents an existing OID.
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The OID is assigned a new number as if it had been created with
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.Fa number
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set to
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.Dv OID_AUTO .
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.Pp
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The
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.Fn sysctl_remove_oid
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function removes a dynamically created OID from the tree and
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optionally freeing its resources.
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It takes the following arguments:
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.Bl -tag -width recurse
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.It Fa oidp
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A pointer to the dynamic OID to be removed.
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If the OID is not dynamic, or the pointer is
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.Dv NULL ,
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the function returns
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.Er EINVAL .
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.It Fa del
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If non-zero,
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.Fn sysctl_remove_oid
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will try to free the OID's resources
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when the reference count of the OID becomes zero.
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However, if
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.Fa del
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is set to 0,
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the routine will only deregister the OID from the tree,
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without freeing its resources.
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This behaviour is useful when the caller expects to rollback
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(possibly partially failed)
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deletion of many OIDs later.
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.It Fa recurse
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If non-zero, attempt to remove the node and all its children.
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If
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.Pa recurse
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is set to 0,
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any attempt to remove a node that contains any children
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will result in a
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.Er ENOTEMPTY
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error.
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.Em WARNING : "use recursive deletion with extreme caution" !
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Normally it should not be needed if contexts are used.
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Contexts take care of tracking inter-dependencies
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between users of the tree.
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However, in some extreme cases it might be necessary
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to remove part of the subtree no matter how it was created,
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in order to free some other resources.
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Be aware, though, that this may result in a system
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.Xr panic 9
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if other code sections continue to use removed subtrees.
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.El
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.Pp
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The
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.Fn sysctl_remove_name
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function looks up the child node matching the
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.Fa name
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argument and then invokes the
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.Fn sysctl_remove_oid
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function on that node, passing along the
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.Fa del
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and
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.Fa recurse
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arguments.
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If a node having the specified name does not exist an error code of
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.Er ENOENT
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is returned.
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Else the error code from
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.Fn sysctl_remove_oid
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is returned.
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.Pp
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In most cases the programmer should use contexts,
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as described in
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.Xr sysctl_ctx_init 9 ,
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to keep track of created OIDs,
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and to delete them later in orderly fashion.
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.Sh SEE ALSO
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.Xr sysctl 8 ,
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.Xr sysctl 9 ,
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.Xr sysctl_ctx_free 9 ,
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.Xr sysctl_ctx_init 9
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.Sh HISTORY
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These functions first appeared in
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.Fx 4.2 .
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.Sh AUTHORS
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.An Andrzej Bialecki Aq Mt abial@FreeBSD.org
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.Sh BUGS
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Sharing nodes between many code sections
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causes interdependencies that sometimes may lock the resources.
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For example,
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if module A hooks up a subtree to an OID created by module B,
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module B will be unable to delete that OID.
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These issues are handled properly by sysctl contexts.
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.Pp
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Many operations on the tree involve traversing linked lists.
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For this reason, OID creation and removal is relatively costly.
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