Dispatch Routine IRQL and Thread Context

　　The following table summarizes the IRQL and thread context requirements for file system filter driver dispatch routines.

DriverEntry routines are called in the context of a system thread at IRQL = PASSIVE_LEVEL.

　　Most drivers' dispatch routines are called in an arbitrary thread context at IRQL = PASSIVE_LEVEL, with the following exceptions:

• Any highest-level driver's dispatch routines are called in the context of the thread that originated the I/O request, which is commonly a user-mode application thread.

  In other words, the dispatch routines of file system drivers and other highest-level drivers are called in a nonarbitrary thread context at IRQL = PASSIVE_LEVEL.

• The DispatchRead , DispatchWrite , and DispatchDeviceControl routines of lowest-level device drivers, and of intermediate drivers layered above them in the system paging path, can be called at IRQL = APC_LEVEL and in an arbitrary thread context.

  The DispatchRead and/or DispatchWrite routines, and any other routine that also processes read and/or write requests in such a lowest-level device or intermediate driver, must be resident at all times . These driver routines can neither be pageable nor be part of a driver's pageable-image section; they must not access any pageable memory . Furthermore, they should not be dependent on any blocking calls (such as KeWaitForSingleObject with a nonzero time-out).

• The DispatchPower routine of drivers in the hibernation and/or paging paths can be called at IRQL = DISPATCH_LEVEL. The DispatchPnP routines of such drivers must be prepared to handle PnP IRP_MN_DEVICE_USAGE_NOTIFICATION requests.
• The DispatchPower routine of drivers that require inrush power at start-up can be called at IRQL = DISPATCH_LEVEL.

 

Dispatch Routine	Caller's IRQL:	Caller's Thread Context:
Cleanup	PASSIVE_LEVEL	Nonarbitrary
Close	APC_LEVEL	Arbitrary
Create	PASSIVE_LEVEL	Nonarbitrary
DeviceControl (except paging I/O)	PASSIVE_LEVEL	Nonarbitrary
DeviceControl (paging I/O path)	APC_LEVEL	Arbitrary
DirectoryControl	APC_LEVEL	Arbitrary
FlushBuffers	PASSIVE_LEVEL	Nonarbitrary
FsControl (except paging I/O)	PASSIVE_LEVEL	Nonarbitrary
FsControl (paging I/O path)	APC_LEVEL	Arbitrary
LockControl	PASSIVE_LEVEL	Nonarbitrary
PnP	PASSIVE_LEVEL	Arbitrary
QueryEa	PASSIVE_LEVEL	Nonarbitrary
QueryInformation	PASSIVE_LEVEL	Nonarbitrary
QueryQuota	PASSIVE_LEVEL	Nonarbitrary
QuerySecurity	PASSIVE_LEVEL	Nonarbitrary
QueryVolumeInfo	PASSIVE_LEVEL	Nonarbitrary
Read (except paging I/O)	PASSIVE_LEVEL	Nonarbitrary
Read (paging I/O path)	APC_LEVEL	Arbitrary
SetEa	PASSIVE_LEVEL	Nonarbitrary
SetInformation	PASSIVE_LEVEL	Nonarbitrary
SetQuota	PASSIVE_LEVEL	Nonarbitrary
SetSecurity	PASSIVE_LEVEL	Nonarbitrary
SetVolumeInfo	PASSIVE_LEVEL	Nonarbitrary
Shutdown	APC_LEVEL	Arbitrary
Write (except paging I/O)	PASSIVE_LEVEL	Nonarbitrary
Write (paging I/O path)	APC_LEVEL	Arbitrary