静下来，定好方向，好好干。
分类： WINDOWS
2008-04-24 13:29:42
is known as the “Interrupt ReQuest Level”. The processor will be executing code in a thread at a particular IRQL. The IRQL of the processor essentially helps determine how that thread is allowed to be interrupted. The thread can only be interrupted by code which needs to run at a higher IRQL on the same processor. Interrupts requiring the same IRQL or lower are masked off so only interrupts requiring a higher IRQL are available for processing. In a multi-processor system, each processor operates independently at its own IRQL.
There are four IRQL levels which you generally will be dealing with, which are “Passive”, “APC”, “Dispatch” and “DIRQL”. Kernel APIs documented in MSDN generally have a note which specifies the IRQL level at which you need to be running in order to use the API. The higher the IRQL you go, the less APIs that are available for use. The documentation on MSDN defines what IRQL the processor will be running at when the particular entry point of the driver is called. “DriverEntry”, for example, will be called at PASSIVE_LEVEL.
This is the lowest IRQL. No interrupts are masked off and this is the level in which a thread executing in user mode is running. Pagable memory is accessible.
APC_LEVEL
In a processor running at this level, only APC level interrupts are masked. This is the level in which occur. Pagable memory is still accessible. When an APC occurs, the processor is raised to APC level. This, in turn, also disables other APCs from occurring. A driver can manually raise its IRQL to APC (or any other level) in order to perform some synchronization with APCs, for example, since APCs can’t be invoked if you are already at APC level. There are some APIs which can’t be called at APC level due to the fact that APCs are disabled, which, in turn, may disable some I/O Completion APCs.
DISPATCH_LEVEL
The processor running at this level has DPC level interrupts and lower masked off. Pagable memory cannot be accessed, so all memory being accessed must be non-paged. If you are running at Dispatch Level, the APIs that you can use greatly decrease since you can only deal with non-paged memory.
(Device IRQL)
Generally, higher level drivers do not deal with IRQLs at this level, but all interrupts at this level or less are masked off and do not occur. This is actually a range of IRQLs, and this is a method to determine which devices have priority over other devices.
