503 lines
13 KiB
Groff
503 lines
13 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 July 15, 2000
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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_remove_oid
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.Nd runtime sysctl tree manipulation
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.Sh SYNOPSIS
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.Fd #include <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 "char *name"
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.Fa "int kind"
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.Fa "void *arg1"
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.Fa "int arg2"
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.Fa "int (*handler) (SYSCTL_HANDLER_ARGS)"
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.Fa "char *format"
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.Fa "char *descr"
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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 struct sysctl_oid_list *
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.Fo SYSCTL_CHILDREN
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.Fa "struct sysctl_oid *oidp"
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.Fc
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.Ft struct sysctl_oid_list *
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.Fo SYSCTL_STATIC_CHILDREN
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.Fa "OID_NAME"
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.Fc
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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 "NAME"
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.Fa "int kind"
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.Fa "void *arg1"
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.Fa "int arg2"
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.Fa "int (*handler) (SYSCTL_HANDLER_ARGS)"
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.Fa "char *format"
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.Fa "char *descr"
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.Fc
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.Ft struct sysctl_oid *
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.Fo SYSCTL_ADD_NODE
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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 "NAME"
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.Fa "int access"
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.Fa "int (*handler) (SYSCTL_HANDLER_ARGS)"
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.Fa "char *descr"
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.Fc
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.Ft struct sysctl_oid *
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.Fo SYSCTL_ADD_STRING
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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 "NAME"
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.Fa "int access"
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.Fa "char *arg"
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.Fa "0"
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.Fa "char *descr"
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.Fc
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.Ft struct sysctl_oid *
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.Fo SYSCTL_ADD_INT
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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 "NAME"
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.Fa "int access"
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.Fa "int *arg"
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.Fa "0"
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.Fa "char *descr"
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.Fc
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.Ft struct sysctl_oid *
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.Fo SYSCTL_ADD_UINT
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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 "NAME"
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.Fa "int access"
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.Fa "unsigned int *arg"
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.Fa "0"
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.Fa "char *descr"
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.Fc
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.Ft struct sysctl_oid *
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.Fo SYSCTL_ADD_LONG
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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 "NAME"
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.Fa "int access"
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.Fa "long *arg"
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.Fa "0"
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.Fa "char *descr"
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.Fc
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.Ft struct sysctl_oid *
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.Fo SYSCTL_ADD_ULONG
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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 "NAME"
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.Fa "int access"
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.Fa "unsigned long *arg"
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.Fa "0"
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.Fa "char *descr"
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.Fc
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.Ft struct sysctl_oid *
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.Fo SYSCTL_ADD_OPAQUE
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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 "NAME"
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.Fa "int access"
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.Fa "void *arg"
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.Fa "size_t *len"
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.Fa "char *format"
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.Fa "char *descr"
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.Fc
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.Ft struct sysctl_oid *
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.Fo SYSCTL_ADD_STRUCT
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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 "NAME"
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.Fa "int access"
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.Fa "struct TYPE *arg"
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.Fa "TYPE"
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.Fa "char *descr"
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.Fc
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.Ft struct sysctl_oid *
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.Fo SYSCTL_ADD_PROC
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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 "NAME"
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.Fa "int access"
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.Fa "0"
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.Fa "0"
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.Fa "int (*handler) (SYSCTL_HANDLER_ARGS)"
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.Fa "char *format"
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.Fa "char *descr"
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.Fc
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.Sh DESCRIPTION
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These functions and macros provide an interface
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for creating and deleting sysctl oids at runtime
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(e.g. during lifetime of a module).
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The alternative method,
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based on linker sets (see
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.Aq sys/linker_set.h
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and
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.\" XXX Manual pages should avoid referencing source files
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.Pa src/sys/kern/kern_sysctl.c
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for details), only allows creation and deletion
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on module load and unload respectively.
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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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Newly created oids are connected to their parent nodes.
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In all these functions and macros
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(with the exception of
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.Fn sysctl_remove_oid ) ,
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one of the required parameters is
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.Fa parent ,
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which points to the head of the parent's list of children.
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.Pp
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Most top level categories are created statically.
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When connecting to existing static oids,
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this pointer can be obtained with the
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.Fn SYSCTL_STATIC_CHILDREN
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macro, where the
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.Fa OID_NAME
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argumwent is name of the parent oid of type
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.Dv CTLTYPE_NODE
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(i.e. the name displayed by
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.Xr sysctl 8 ,
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preceded by underscore, and with all dots replaced with underscores).
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.Pp
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When connecting to an existing dynamic oid, this pointer
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can be obtained with the
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.Fn SYSCTL_CHILDREN
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macro, where the
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.Fa oidp
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argument points to the parent oid of type
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.Dv CTLTYPE_NODE .
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.Pp
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The
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.Fn sysctl_add_oid
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function creates raw oids of any type.
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If the oid is successfuly created,
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the function returns a pointer to it;
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otherwise 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 macros.
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The arguments are as follows:
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.Bl -tag -width handler
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.It Fa ctx
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A pointer to an optional sysctl context, or
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.Dv NULL .
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See
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.Xr sysctl_ctx_init 9
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for details.
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Programmers are strongly advised to use contexts
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to organize the dynamic oids which they create,
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unless special creation and deletion sequences are required.
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If
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.Fa ctx
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is not
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.Dv NULL ,
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the newly created oid will be added to this context
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as its first entry.
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.It Fa parent
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A pointer to a
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.Li struct sysctl_oid_list ,
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which is the head of the parent's list of children.
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.It Fa number
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The oid number that will be assigned to this oid.
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In almost all cases this should be set to
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.Dv OID_AUTO ,
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which will result in the assignment of the next available oid number.
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.It Fa name
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The name of the oid.
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The newly created oid will contain a copy of the name.
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.It Fa kind
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The kind of oid,
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specified as a bitmask of the type and access values defined in the
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.Aq sys/sysctl.h
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header file.
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Oids created dynamically always have the
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.Dv CTLTYPE_DYN
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flag set.
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Access flags specify whether this oid is read-only or read-write,
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and whether it may be modified by all users
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or by the supseruser only.
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.It Fa arg1
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A pointer to any data that the oid should reference, or
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.Dv NULL .
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.It Fa arg2
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The size of
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.Fa arg1 ,
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or 0 if
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.Fa arg1
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is
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.Dv NULL .
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.It Fa handler
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A pointer to the function
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that is responsible for handling read and write requests
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to this oid.
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There are several standard handlers
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that support operations on nodes,
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integers, strings and opaque objects.
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It is possible also to define new handlers using the
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.Fn SYSCTL_ADD_PROC
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macro.
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.It Fa format
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A pointer to a string
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which specifies the format of the oid symbolically.
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This format is used as a hint by
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.Xr sysctl 8
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to apply proper data formatting for display purposes.
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Currently used format names are:
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.Dq N
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for node,
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.Dq A
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for
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.Li "char *" ,
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.Dq I
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for
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.Li "int" ,
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.Dq IU
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for
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.Li "unsigned int" ,
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.Dq L
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for
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.Li "long" ,
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.Dq LU
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for
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.Li "unsigned long"
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and
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.Dq S,TYPE
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for
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.Li "struct TYPE"
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structures.
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.It Fa descr
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A pointer to a textual description of the oid.
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.El
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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,
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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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.\" XXX sheldonh finished up to here
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Again, 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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.Pp
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There is a set of macros defined
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that helps to create oids of given type.
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.Bl -tag -width SYSCTL_ADD_STRINGXX
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They are as follows:
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.It Fn SYSCTL_ADD_OID
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creates a raw oid.
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This macro is functionally equivalent to the
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.Fn sysctl_add_oid
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function.
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.It Fn SYSCTL_ADD_NODE
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creates an oid of type
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.Dv CTLTYPE_NODE ,
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to which child oids may be added.
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.It Fn SYSCTL_ADD_STRING
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creates an oid that handles a zero-terminated character string.
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.It Fn SYSCTL_ADD_INT
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creates an oid that handles an
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.Li int
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variable.
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.It Fn SYSCTL_ADD_UINT
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creates an oid that handles an
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.Li unsigned int
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variable.
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.It Fn SYSCTL_ADD_LONG
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creates an oid that handles a
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.Li long
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variable.
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.It Fn SYSCTL_ADD_ULONG
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creates an oid that handles an
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.Li unsigned long
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variable.
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.It Fn SYSCTL_ADD_OPAQUE
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creates an oid that handles any chunk of opaque data
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of the size specified by the
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.Fa len
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argument,
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which is a pointer to a
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.Li "size_t *" .
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.It Fn SYSCTL_ADD_STRUCT
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creates an oid that handles a
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.Li "struct TYPE"
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structure.
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The
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.Fa format
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parameter will be set to
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.Dq S,TYPE
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to provide proper hints to the
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.Xr sysctl 8
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utility.
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.It Fn SYSCTL_ADD_PROC
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creates an oid with the specified
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.Pa handler
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function.
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The handler is responsible for handling read and write requests
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to the oid.
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This oid type is especially useful
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if the kernel data is not easily accessible,
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or needs to be processed before exporting.
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.El
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.Sh EXAMPLES
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The following is an example of
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how to create a new top-level category
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and how to hook up another subtree to an existing static node.
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This example does not use contexts,
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which results in tedious management of all intermediate oids,
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as they need to be freed later on:
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.Bd -literal
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#include <sys/sysctl.h>
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...
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/* Need to preserve pointers to newly created subtrees, to be able
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* to free them later.
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*/
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struct sysctl_oid *root1, *root2, *oidp;
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int a_int;
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char *string = "dynamic sysctl";
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...
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root1 = SYSCTL_ADD_NODE( NULL, SYSCTL_STATIC_CHILDREN(/* tree top */),
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OID_AUTO, "newtree", CTLFLAG_RW, 0, "new top level tree");
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oidp = SYSCTL_ADD_INT( NULL, SYSCTL_CHILDREN(root1),
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OID_AUTO, "newint", CTLFLAG_RW, &a_int, 0, "new int leaf");
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...
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root2 = SYSCTL_ADD_NODE( NULL, SYSCTL_STATIC_CHILDREN(_debug),
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OID_AUTO, "newtree", CTLFLAG_RW, 0, "new tree under debug");
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oidp = SYSCTL_ADD_STRING( NULL, SYSCTL_CHILDREN(root2),
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OID_AUTO, "newstring", CTLFLAG_RD, string, 0, "new string leaf");
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.Ed
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.Pp
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This example creates the following subtrees:
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.Bd -literal -offset indent
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debug.newtree.newstring
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newtree.newint
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.Ed
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.Pp
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.Em "Care should be taken to free all oids once they are no longer needed!"
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.Sh SEE ALSO
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.Xr sysctl 8 ,
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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 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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