113 lines
4.0 KiB
Groff
113 lines
4.0 KiB
Groff
.\" $NetBSD: callback.9,v 1.5 2010/12/02 12:54:13 wiz Exp $
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.\"
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.\" Copyright (c) 2009 The NetBSD Foundation, Inc.
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd October 28, 2009
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.Dt CALLBACK 9
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.Os
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.Sh NAME
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.Nm callback
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.Nd generic callback interface
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.Sh SYNOPSIS
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.In sys/callback.h
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.Ft void
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.Fn callback_head_init "struct callback_head *ch" "int ipl"
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.Ft void
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.Fn callback_head_destroy "struct callback_head *ch"
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.Ft void
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.Fn callback_register \
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"struct callback_head *ch" "struct callback_entry *ce" "void *obj" \
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"int (*fn)(struct callback_entry *, void *, void *)"
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.Ft void
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.Fn callback_unregister "struct callback_head *ch" "struct callback_entry *ce"
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.Ft int
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.Fn callback_run_roundrobin "struct callback_head *ch" "void *arg"
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.Sh DESCRIPTION
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The generic
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.Nm callback
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interface allows lower-level layer code to execute a registered function,
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or set of functions, from the higher-level layer.
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.Pp
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Registered functions must return one of these constants:
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.Bl -tag -width Dv
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.It Dv CALLBACK_CHAIN_CONTINUE
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Indicates that the function call was successful.
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The following functions in the chain will be called.
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.It Dv CALLBACK_CHAIN_ABORT
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Indicates a failure case in the function call.
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Any following functions in the chain will not be executed.
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.El
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.Sh FUNCTIONS
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The callback structure
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.Vt callback_head
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should be initialized and destroyed using the functions described below.
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This structure contains the list of callback entries and other internal data.
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.Pp
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The
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.Vt callback_entry
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structure is an entry, normally associated with the higher-level object.
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It contains the internal data of the callback interface.
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.Bl -tag -width compact
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.It Fn callback_head_init "ch" "ipl"
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Initialize the callback structure specified by
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.Fa ch .
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The highest IPL at which this callback can be used is specified by
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.Fa ipl .
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.It Fn callback_head_destroy "ch"
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Destroy the callback structure specified by
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.Fa ch .
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The caller must unregister all functions before destroying the callback structure.
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.It Fn callback_register "ch" "ce" "obj" "fn"
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Register the callback function in the callback structure specified by
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.Fa ch .
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.Fa ce
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should point to the entry structure of the callback object.
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The callback object itself is specified by
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.Fa obj .
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The function pointer is specified by
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.Fa fn .
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.It Fn callback_unregister "ch" "ce"
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Unregister the callback function from the structure specified by
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.Fa ch .
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The entry should be passed as
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.Fa ce .
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This function may block.
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.It Fn callback_run_roundrobin "ch" "arg"
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Executes all functions registered in the callback
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structure, specified by
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.Fa ch .
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The functions are executed in round-robin fashion.
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The value of
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.Fa arg
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will be passed to the callback functions.
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.El
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.Sh CODE REFERENCES
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The
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.Nm
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interface is implemented within the file
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.Pa sys/kern/subr_callback.c .
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.Sh SEE ALSO
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.Xr intro 9
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