powerhook_establish(9) - NetBSD Manual Pages

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POWERHOOK_ESTABLISH(9)       NetBSD Kernel Manual       POWERHOOK_ESTABLISH(9)


NAME

     powerhook_establish, powerhook_disestablish - add or remove a power
     change hook


SYNOPSIS

     void *
     powerhook_establish(void (*fn)(int why, void *a), void *arg);

     void
     powerhook_disestablish(void *cookie);


DESCRIPTION

     The powerhook_establish() function adds fn of the list of hooks invoked
     by dopowerhooks(9) at power change.  When invoked, the hook function fn
     will be passed the new power state as the first argument and arg as its
     second argument.

     The powerhook_disestablish() function removes the hook described by the
     opaque pointer cookie from the list of hooks to be invoked at power
     change.  If cookie is invalid, the result of powerhook_disestablish() is
     undefined.

     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, shutdown hooks cannot rely on many system services
     (including file systems, and timeouts and other interrupt-driven ser-
     vices).  The power hooks are typically executed from an interrupt con-
     text.

     The different reasons for calling the power hooks are: suspend, standby,
     and resume.  The reason is reflected in the why argument and the values
     PWR_SOFTSUSPEND, PWR_SUSPEND, PWR_SOFTSTANDBY, PWR_STANDBY,
     PWR_SOFTRESUME, and PWR_RESUME.  It calls with PWR_SOFTxxx in the normal
     priority level while the other callings are protected with splhigh(9).
     At suspend the system is going to lose (almost) all power, standby re-
     tains some power (e.g., minimal power to USB devices), and at resume pow-
     er is back to normal.


RETURN VALUES

     If successful, powerhook_establish() returns an opaque pointer describing
     the newly-established shutdown hook.  Otherwise, it returns NULL.


SEE ALSO

     dopowerhooks(9)

NetBSD 1.6                     December 3, 1999                              1