PoCallDriver function (ntifs.h)
The PoCallDriver routine passes a power IRP to the next-lower driver in the device stack. (Windows Server 2003, Windows XP, and Windows 2000 only.)
NTSTATUS PoCallDriver( [in] PDEVICE_OBJECT DeviceObject, [in, out] __drv_aliasesMem PIRP Irp );
A pointer to the driver-created DEVICE_OBJECT to which the IRP is to be routed.
[in, out] Irp
A pointer to an IRP.
PoCallDriver returns STATUS_SUCCESS to indicate success. It returns STATUS_PENDING if it has queued the IRP.
Beginning with Windows Vista, drivers should call IoCallDriver, not PoCallDriver to pass a power IRP to the next-lower driver. However, on Windows Server 2003, Windows XP, and Windows 2000, drivers must call PoCallDriver, not IoCallDriver to pass a power IRP to the next-lower driver. On Windows Server 2003, Windows XP, an Windows 2000, drivers must also call PoStartNextPowerIrp before calling PoCallDriver.
A driver that requires a new IRP should call PoRequestPowerIrp. A driver must not allocate its own power IRP.
When passing a power IRP down to the next-lower driver, the caller should use IoSkipCurrentIrpStackLocation or IoCopyCurrentIrpStackLocationToNext to set the IRP stack location, then call PoCallDriver. Use IoCopyCurrentIrpStackLocationToNext if processing the IRP requires setting an IoCompletion routine, or IoSkipCurrentStackLocation if no IoCompletion routine is required.
When a device is powering up, its drivers must set IoCompletion routines to perform start-up tasks (initializing the device, restoring context, and so on) after the bus driver has set the device in the working state. Set IoCompletion routines before calling PoCallDriver.
When a device is powering down, its drivers must perform necessary power-down tasks before passing the IRP to the next lower driver. After the IRP has reached the bus driver, the device will be powered off and its drivers will no longer have access to it. On Windows Server 2003, Windows XP, and Windows 2000, an IoCompletion routine that is associated with a power-down IRP is only required to call PoStartNextPowerIrp.
Only one inrush IRP can be active in the system at a time. When passing a power-up IRP for a device that requires inrush current (in other words, the DO_POWER_INRUSH flag is set in the device object), PoCallDriver checks whether another inrush IRP is already active. If so, PoCallDriver queues the current IRP for handling after the previous IRP completes, and then returns STATUS_PENDING. For more information about inrush IRPs, see Setting Device Object Flags for Power Management.
On Windows 2000 and later systems, pageable drivers (the DO_POWER_PAGABLE flag is set in the device object) must call PoCallDriver at IRQL = PASSIVE_LEVEL. Drivers that cannot be paged (DO_POWER_PAGABLE is not set in the device object) or that require inrush current (DO_POWER_INRUSH is set in the device object) can call PoCallDriver at IRQL = PASSIVE_LEVEL or DISPATCH_LEVEL.
On Windows 98/Me, all drivers call PoCallDriver at IRQL = PASSIVE_LEVEL.