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:
1. 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.
2.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).
3. The DispatchPower routine of drivers in the hibernation and/or paging paths can be called at IRQL = DISPATCH_LEVEL. TheDispatchPnP routines of such drivers must be prepared to handle PnP IRP_MN_DEVICE_USAGE_NOTIFICATION requests.
4. 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 |
IRQL等級：
PASSIVE_LEVEL：普通線程執行的中斷等級；
APC_LEVEL：異步過程調用等級；
DISPATCH_LEVEL：線程分派（調度）和延遲過程調用中斷等級。在此等級和更高等級上線程調度會被掛起（不再有線程調度）。此等級上不能使用分頁內存。