439 lines
11 KiB
Groff
439 lines
11 KiB
Groff
.\"
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.\" Copyright (c) 2010-2011 The FreeBSD Foundation
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.\" All rights reserved.
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.\"
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.\" This documentation was written at the Centre for Advanced Internet
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.\" Architectures, Swinburne University of Technology, Melbourne, Australia by
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.\" David Hayes and Lawrence Stewart under sponsorship from the FreeBSD
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.\" Foundation.
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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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.\"
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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 FOR
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.\" 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 February 15, 2011
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.Dt KHELP 9
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.Os
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.Sh NAME
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.Nm khelp ,
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.Nm khelp_init_osd ,
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.Nm khelp_destroy_osd ,
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.Nm khelp_get_id ,
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.Nm khelp_get_osd ,
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.Nm khelp_add_hhook ,
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.Nm khelp_remove_hhook ,
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.Nm KHELP_DECLARE_MOD ,
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.Nm KHELP_DECLARE_MOD_UMA
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.Nd Kernel Helper Framework
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.Sh SYNOPSIS
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.In sys/khelp.h
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.In sys/module_khelp.h
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.Fn "int khelp_init_osd" "uint32_t classes" "struct osd *hosd"
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.Fn "int khelp_destroy_osd" "struct osd *hosd"
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.Fn "int32_t khelp_get_id" "char *hname"
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.Fn "void * khelp_get_osd" "struct osd *hosd" "int32_t id"
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.Fn "int khelp_add_hhook" "struct hookinfo *hki" "uint32_t flags"
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.Fn "int khelp_remove_hhook" "struct hookinfo *hki"
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.Fn KHELP_DECLARE_MOD "hname" "hdata" "hhooks" "version"
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.Fn KHELP_DECLARE_MOD_UMA "hname" "hdata" "hhooks" "version" "ctor" "dtor"
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.Sh DESCRIPTION
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.Nm
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provides a framework for managing
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.Nm
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modules, which indirectly use the
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.Xr hhook 9
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KPI to register their hook functions with hook points of interest within the
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kernel.
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Khelp modules aim to provide a structured way to dynamically extend the kernel
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at runtime in an ABI preserving manner.
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Depending on the subsystem providing hook points, a
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.Nm
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module may be able to associate per-object data for maintaining relevant state
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between hook calls.
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The
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.Xr hhook 9
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and
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.Nm
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frameworks are tightly integrated and anyone interested in
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.Nm
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should also read the
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.Xr hhook 9
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manual page thoroughly.
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.Ss Information for Khelp Module Implementors
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.Nm
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modules are represented within the
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.Nm
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framework by a
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.Vt struct helper
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which has the following members:
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.Bd -literal -offset indent
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struct helper {
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int (*mod_init) (void);
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int (*mod_destroy) (void);
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#define HELPER_NAME_MAXLEN 16
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char h_name[HELPER_NAME_MAXLEN];
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uma_zone_t h_zone;
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struct hookinfo *h_hooks;
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uint32_t h_nhooks;
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uint32_t h_classes;
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int32_t h_id;
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volatile uint32_t h_refcount;
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uint16_t h_flags;
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TAILQ_ENTRY(helper) h_next;
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};
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.Ed
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.Pp
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Modules must instantiate a
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.Vt struct helper ,
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but are only required to set the
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.Va h_classes
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field, and may optionally set the
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.Va h_flags ,
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.Va mod_init
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and
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.Va mod_destroy
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fields where required.
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The framework takes care of all other fields and modules should refrain from
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manipulating them.
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Using the C99 designated initialiser feature to set fields is encouraged.
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.Pp
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If specified, the
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.Va mod_init
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function will be run by the
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.Nm
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framework prior to completing the registration process.
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Returning a non-zero value from the
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.Va mod_init
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function will abort the registration process and fail to load the module.
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If specified, the
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.Va mod_destroy
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function will be run by the
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.Nm
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framework during the deregistration process, after the module has been
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deregistered by the
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.Nm
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framework.
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The return value is currently ignored.
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Valid
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.Nm
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classes are defined in
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.In sys/khelp.h .
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Valid flags are defined in
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.In sys/module_khelp.h .
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The HELPER_NEEDS_OSD flag should be set in the
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.Va h_flags
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field if the
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.Nm
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module requires persistent per-object data storage.
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There is no programmatic way (yet) to check if a
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.Nm
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class provides the ability for
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.Nm
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modules to associate persistent per-object data, so a manual check is required.
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.Pp
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The
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.Fn KHELP_DECLARE_MOD
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and
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.Fn KHELP_DECLARE_MOD_UMA
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macros provide convenient wrappers around the
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.Xr DECLARE_MODULE 9
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macro, and are used to register a
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.Nm
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module with the
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.Nm
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framework.
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.Fn KHELP_DECLARE_MOD_UMA
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should only be used by modules which require the use of persistent per-object
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storage i.e. modules which set the HELPER_NEEDS_OSD flag in their
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.Vt struct helper Ns 's
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.Va h_flags
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field.
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.Pp
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The first four arguments common to both macros are as follows.
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The
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.Fa hname
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argument specifies the unique
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.Xr ascii 7
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name for the
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.Nm
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module.
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It should be no longer than HELPER_NAME_MAXLEN-1 characters in length.
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The
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.Fa hdata
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argument is a pointer to the module's
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.Vt struct helper .
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The
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.Fa hhooks
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argument points to a static array of
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.Vt struct hookinfo
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structures.
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The array should contain a
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.Vt struct hookinfo
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for each
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.Xr hhook 9
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point the module wishes to hook, even when using the same hook function multiple
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times for different
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.Xr hhook 9
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points.
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The
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.Fa version
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argument specifies a version number for the module which will be passed to
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.Xr MODULE_VERSION 9 .
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The
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.Fn KHELP_DECLARE_MOD_UMA
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macro takes the additional
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.Fa ctor
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and
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.Fa dtor
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arguments, which specify optional
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.Xr uma 9
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constructor and destructor functions.
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NULL should be passed where the functionality is not required.
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.Pp
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The
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.Fn khelp_get_id
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function returns the numeric identifier for the
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.Nm
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module with name
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.Fa hname .
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.Pp
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The
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.Fn khelp_get_osd
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function is used to obtain the per-object data pointer for a specified
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.Nm
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module.
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The
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.Fa hosd
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argument is a pointer to the underlying subsystem object's
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.Vt struct osd .
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This is provided by the
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.Xr hhook 9
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framework when calling into a
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.Nm
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module's hook function.
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The
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.Fa id
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argument specifies the numeric identifier for the
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.Nm
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module to extract the data pointer from
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.Fa hosd
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for.
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The
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.Fa id
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is obtained using the
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.Fn khelp_get_id
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function.
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.Pp
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The
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.Fn khelp_add_hhook
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and
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.Fn khelp_remove_hhook
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functions allow a
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.Nm
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module to dynamically hook/unhook
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.Xr hhook 9
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points at run time.
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The
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.Fa hki
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argument specifies a pointer to a
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.Vt struct hookinfo
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which encapsulates the required information about the
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.Xr hhook 9
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point and hook function being manipulated.
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The HHOOK_WAITOK flag may be passed in via the
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.Fa flags
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argument of
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.Fn khelp_add_hhook
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if
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.Xr malloc 9
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is allowed to sleep waiting for memory to become available.
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.Ss Integrating Khelp Into a Kernel Subsystem
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Most of the work required to allow
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.Nm
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modules to do useful things relates to defining and instantiating suitable
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.Xr hhook 9
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points for
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.Nm
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modules to hook into.
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The only additional decision a subsystem needs to make is whether it wants to
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allow
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.Nm
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modules to associate persistent per-object data.
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Providing support for persistent data storage can allow
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.Nm
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modules to perform more complex functionality which may be desirable.
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Subsystems which want to allow Khelp modules to associate
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persistent per-object data with one of the subsystem's data structures need to
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make the following two key changes:
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.Bl -bullet
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.It
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Embed a
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.Vt struct osd
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pointer in the structure definition for the object.
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.It
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Add calls to
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.Fn khelp_init_osd
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and
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.Fn khelp_destroy_osd
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to the subsystem code paths which are responsible for respectively initialising
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and destroying the object.
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.El
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.Pp
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The
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.Fn khelp_init_osd
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function initialises the per-object data storage for all currently loaded
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.Nm
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modules of appropriate classes which have set the HELPER_NEEDS_OSD flag in their
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.Va h_flags
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field.
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The
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.Fa classes
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argument specifies a bitmask of
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.Nm
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classes which this subsystem associates with.
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If a
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.Nm
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module matches any of the classes in the bitmask, that module will be associated
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with the object.
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The
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.Fa hosd
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argument specifies the pointer to the object's
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.Vt struct osd
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which will be used to provide the persistent storage for use by
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.Nm
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modules.
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.Pp
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The
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.Fn khelp_destroy_osd
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function frees all memory that was associated with an object's
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.Vt struct osd
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by a previous call to
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.Fn khelp_init_osd .
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The
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.Fa hosd
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argument specifies the pointer to the object's
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.Vt struct osd
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which will be purged in preparation for destruction.
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.Sh IMPLEMENTATION NOTES
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.Nm
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modules are protected from being prematurely unloaded by a reference count.
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The count is incremented each time a subsystem calls
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.Fn khelp_init_osd
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causing persistent storage to be allocated for the module, and decremented for
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each corresponding call to
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.Fn khelp_destroy_osd .
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Only when a module's reference count has dropped to zero can the module be
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unloaded.
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.Sh RETURN VALUES
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The
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.Fn khelp_init_osd
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function returns zero if no errors occurred.
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It returns ENOMEM if a
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.Nm
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module which requires per-object storage fails to allocate the necessary memory.
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.Pp
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The
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.Fn khelp_destroy_osd
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function only returns zero to indicate that no errors occurred.
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.Pp
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The
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.Fn khelp_get_id
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function returns the unique numeric identifier for the registered
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.Nm
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module with name
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.Fa hname .
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It return -1 if no module with the specified name is currently registered.
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.Pp
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The
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.Fn khelp_get_osd
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function returns the pointer to the
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.Nm
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module's persistent object storage memory.
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If the module identified by
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.Fa id
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does not have persistent object storage registered with the object's
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.Fa hosd
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.Vt struct osd ,
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NULL is returned.
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.Pp
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The
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.Fn khelp_add_hhook
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function returns zero if no errors occurred.
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It returns ENOENT if it could not find the requested
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.Xr hhook 9
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point.
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It returns ENOMEM if
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.Xr malloc 9
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failed to allocate memory.
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It returns EEXIST if attempting to register the same hook function more than
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once for the same
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.Xr hhook 9
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point.
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.Pp
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The
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.Fn khelp_remove_hhook
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function returns zero if no errors occurred.
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It returns ENOENT if it could not find the requested
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.Xr hhook 9
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point.
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.Sh EXAMPLES
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A well commented example Khelp module can be found at:
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.Pa /usr/share/examples/kld/khelp/h_example.c
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.Pp
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The Enhanced Round Trip Time (ERTT)
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.Xr h_ertt 4
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.Nm
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module provides a more complex example of what is possible.
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.Sh SEE ALSO
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.Xr h_ertt 4 ,
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.Xr hhook 9 ,
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.Xr osd 9
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.Sh ACKNOWLEDGEMENTS
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Development and testing of this software were made possible in part by grants
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from the FreeBSD Foundation and Cisco University Research Program Fund at
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Community Foundation Silicon Valley.
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.Sh HISTORY
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The
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.Nm
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kernel helper framework first appeared in
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.Fx 9.0 .
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.Pp
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The
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.Nm
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framework was first released in 2010 by Lawrence Stewart whilst studying at
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Swinburne University of Technology's Centre for Advanced Internet Architectures,
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Melbourne, Australia.
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More details are available at:
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.Pp
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http://caia.swin.edu.au/urp/newtcp/
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm
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framework was written by
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.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org .
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.Pp
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This manual page was written by
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.An David Hayes Aq Mt david.hayes@ieee.org
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and
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.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org .
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