97 lines
3.7 KiB
Groff
97 lines
3.7 KiB
Groff
.\" $NetBSD: powerhook_establish.9,v 1.1 1999/12/06 14:50:02 augustss Exp $
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.\"
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.\" Copyright (c) 1999 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Lennart Augustsson.
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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. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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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 December 3, 1999
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.Dt POWERHOOK_ESTABLISH 9
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.Os
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.Sh NAME
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.Nm powerhook_establish ,
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.Nm powerhook_disestablish
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.Nd add or remove a power change hook
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.Sh SYNOPSIS
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.Ft void *
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.Fn powerhook_establish "void (*fn)(int why, void *a)" "void *arg"
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.Ft void
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.Fn powerhook_disestablish "void *cookie"
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.Sh DESCRIPTION
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The
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.Fn powerhook_establish
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function adds
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.Fa fn
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of the list of hooks invoked by
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.Xr dopowerhooks 9
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at power change. When invoked, the hook function
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.Fa fn
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will be passed the new power state as the first argument and
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.Fa arg
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as its second argument.
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.Pp
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The
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.Fn powerhook_disestablish
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function removes the hook described by the opaque pointer
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.Fa cookie
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from the list of hooks to be invoked at power change. If
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.Fa cookie
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is invalid, the result of
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.Fn powerhook_disestablish
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is undefined.
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.Pp
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Power hooks should be used to perform activities
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that must happen when the power situation to the computer changes. Because
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of the environment in which they are run, shutdown hooks cannot
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rely on many system services (including file systems, and timeouts
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and other interrupt-driven services).
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The power hooks are typically executed from an interrut context.
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.Pp
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The different reasons for calling the power hooks are: suspend, standby, and
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resume. The reason is reflected in the
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.Fa why
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argument and the values
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.Dv PWR_SUSPEND ,
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.Dv PWR_STANDBY ,
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and
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.Dv PWR_RESUME .
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At suspend the system is going to lose (almost) all power, standby retains
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some power (e.g., minimal power to USB devices), and at resume power is
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back to normal.
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.Sh RETURN VALUES
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If successful,
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.Fn powerhook_establish
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returns an opaque pointer describing the newly-established
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shutdown hook. Otherwise, it returns NULL.
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.Sh SEE ALSO
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.Xr dopowerhooks 9
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