I/O Verification

Driver Verifier has three levels of I/O Verification:

• Level 1 I/O Verification is always active whenever I/O Verification is selected.
• Level 2 I/O Verification is always active whenever I/O Verification is selected in Windows XP and later. In Windows 2000, I/O Verification can be configured to include both levels, or just the Level 1 tests.
• Enhanced I/O Verification can be activated separately from the basic two I/O Verification levels in Windows XP and later. It is not available in Windows 2000.

The effects of each level will be described separately.

Level 1 I/O Verification

When Level 1 I/O Verification is enabled, all IRPs obtained through IoAllocateIrp are allocated from a special pool and their use is tracked.

Additionally, Driver Verifier checks for invalid I/O calls, including:

• Attempts to free an IRP whose type is not IO_TYPE_IRP
• Passes of invalid device objects to IoCallDriver
• Passes of an IRP to IoCompleteRequest that contains invalid status or that still has a cancel routine set
• Changes to the IRQL across a call to the driver dispatch routine
• Attempts to free an IRP that remains associated with a thread
• Passes of a device object to IoInitializeTimer that already contains an initialized timer
• Passes of an invalid buffer to IoBuildAsynchronousFsdRequest or IoBuildDeviceIoControlRequest
• Passes of an I/O status block to an IRP, when this I/O status block is allocated on a stack that has unwound too far
• Passes of an event object to an IRP, when this event object is allocated on a stack that has unwound too far

Because the special IRP pool is of limited size, I/O Verification is most effective when it is only used on one driver at a time.

I/O Verification Level 1 failures cause bug check 0xC9 to be issued. The first parameter of this bug check indicates what violation has occurred. See Bug Check 0xC9 (DRIVER_VERIFIER_IOMANAGER_VIOLATION) for a full parameter listing.

Level 2 I/O Verification

I/O Verification Level 2 errors are displayed in different ways: on the blue screen, in a crash dump file, and in a kernel debugger.

On the blue screen, these errors are noted by the message IO SYSTEM VERIFICATION ERROR and the string WDM DRIVER ERROR XXX, where XXX is an I/O error code.

In a crash dump file, these errors are noted by the message BugCheck 0xC9 (DRIVER_VERIFIER_IOMANAGER_VIOLATION), along with the I/O error code. In this case, the I/O error code appears as the first parameter of the bug check 0xC9.

In a kernel debugger (KD or WinDbg), these errors are noted by the message WDM DRIVER ERROR and a descriptive text string. When the kernel debugger is active, it is possible to ignore the Level 2 errors and resume system operation. (This is not possible with any other bug checks.)

The blue screen, the crash dump file, and the kernel debugger each display additional information as well. For a full description of all I/O Verification Level 2 error messages, see Bug Check 0xC9.

Enhanced I/O Verification

This option is only available in Windows XP and later.

The Enhanced I/O Verification option includes some new parameter verifications, as well as some new stresses and tests.

New parameter verifications include:

• Monitoring all IRPs for correct use of IoMarkPending. (Drivers should return STATUS_PENDING if and only if they have called IoMarkPending.)
• Monitoring the use of IoDeleteDevice, to catch double-deletions and inappropriate detaching and deleting of device objects.
• Unwinding all IoSkipCurrentIrpStackLocation calls.

New stresses and tests include:

• Scrambling the order of enumerated devices, to ensure that Plug and Play (PnP) drivers don't make assumptions about the device start order.
• Adjusting the status of PnP and Power IRPs when they complete, to catch drivers that return an incorrect status from their dispatch routines.
• Sending fake Power IRPs to test for driver code path bugs.
• Sending fake WMI IRPs to test for driver code path bugs.
• Inserting a fake filter into every WDM stack.

Driver errors caught by Enhanced I/O Verification are displayed in the same manner as those caught by Level 2 I/O Verification.

Activating This Option

The I/O Verification option can be activated by using the Driver Verifier Manager graphical interface or the verifier.exe command line. This activation will take effect after the next boot.

When you activate I/O Verification in Windows 2000, you can choose between Level 1 and Level 2; if you choose the latter, both levels of tests are activated.

In Windows XP and later, choosing I/O Verification enables both Level 1 and Level 2 tests. You can activate Enhanced I/O Verification in addition to (or instead of) the standard I/O Verification.

See Selecting Driver Verifier Options for details.

Graphics Drivers

The I/O Verification option is not used for graphics drivers. If selected, it has no effect.