NetBSD-5.0.2/share/man/man9/powerhook_establish.9

.\"	$NetBSD: powerhook_establish.9,v 1.9 2008/04/30 13:10:58 martin Exp $
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.Dd September 24, 2006
.Dt POWERHOOK_ESTABLISH 9
.Os
.Sh NAME
.Nm powerhook_establish ,
.Nm powerhook_disestablish
.Nd add or remove a power change hook
.Sh SYNOPSIS
.Ft void *
.Fn powerhook_establish "const char *name" "void (*fn)(int why, void *a)" \
"void *arg"
.Ft void
.Fn powerhook_disestablish "void *cookie"
.Sh DESCRIPTION
The
.Fn powerhook_establish
function adds
.Fa fn
of the list of hooks invoked by
.Xr dopowerhooks 9
at power change.
When invoked, the hook function
.Fa fn
will be passed the new power state as the first argument and
.Fa arg
as its second argument.
.Pp
The
.Fn powerhook_disestablish
function removes the hook described by the opaque pointer
.Fa cookie
from the list of hooks to be invoked at power change.
If
.Fa cookie
is invalid, the result of
.Fn powerhook_disestablish
is undefined.
.Pp
Power hooks should be used to perform activities
that must happen when the power situation to the computer changes.
Because of the environment in which they are run, power hooks cannot
rely on many system services (including file systems, and timeouts
and other interrupt-driven services).
The power hooks are typically executed from an interrupt context.
.Pp
The different reasons for calling the power hooks are: suspend, standby, and
resume.
The reason is reflected in the
.Fa why
argument and the values
.Dv PWR_SOFTSUSPEND ,
.Dv PWR_SUSPEND ,
.Dv PWR_SOFTSTANDBY ,
.Dv PWR_STANDBY ,
.Dv PWR_SOFTRESUME ,
and
.Dv PWR_RESUME .
It calls with PWR_SOFTxxx in the normal priority level while the other
callings are protected with
.Xr splhigh 9 .
At suspend the system is going to lose (almost) all power, standby retains
some power (e.g., minimal power to USB devices), and at resume power is
back to normal.
.Sh RETURN VALUES
If successful,
.Fn powerhook_establish
returns an opaque pointer describing the newly-established
power hook.
Otherwise, it returns NULL.
.Sh SEE ALSO
.Xr dopowerhooks 9