2e5ad04e96
I'm currently working on writing a metrics exporter for the Prometheus
monitoring system to provide access to sysctl metrics. Prometheus and
sysctl have some structural differences:
- sysctl is a tree of string component names.
- Prometheus uses a flat namespace for its metrics, but allows you to
attach labels with values to them, so that you can do aggregation.
An initial version of my exporter simply translated
hw.acpi.thermal.tz1.temperature
to
sysctl_hw_acpi_thermal_tz1_temperature_celcius
while we should ideally have
sysctl_hw_acpi_thermal_temperature_celcius{thermal_zone="tz1"}
allowing you to graph all thermal zones on a system in one go.
The change presented in this commit adds support for accomplishing this,
by providing the ability to attach labels to nodes. In the example I
gave above, the label "thermal_zone" would be attached to "tz1". As this
is a feature that will only be used very rarely, I decided to not change
the KPI too aggressively.
Discussed on: hackers@
Reviewed by: cem
Differential Revision: https://reviews.freebsd.org/D8775
204 lines
6.0 KiB
Groff
204 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 December 13, 2016
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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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.Fa "const char *label"
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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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