NtSetSystemPowerState - NtDoc

#ifndef _NTPOAPI_H

/**
 * Initiates a power action of the current system. Depending on the Flags parameter, the function either 
 * suspends operation immediately or requests permission from all applications and device drivers before doing so.
 *
 * @param SystemAction The system power action.
 * @param LightestSystemState The lightest system power state.
 * @param Flags Flags for the power action.
 * @return Successful or errant status.
 */
NTSYSCALLAPI
NTSTATUS
NTAPI
NtSetSystemPowerState(
    _In_ POWER_ACTION SystemAction,
    _In_ SYSTEM_POWER_STATE LightestSystemState,
    _In_ ULONG Flags // POWER_ACTION_* flags
    );

#endif
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#ifndef _NTZWAPI_H

NTSYSCALLAPI
NTSTATUS
NTAPI
ZwSetSystemPowerState(
    _In_ POWER_ACTION SystemAction,
    _In_ SYSTEM_POWER_STATE LightestSystemState,
    _In_ ULONG Flags // POWER_ACTION_* flags
    );

#endif
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