Call WDM service from VXD
Calling WDM Services from Windows 98 VxDs
If you are developing VxDs specifically for Windows 98, you might
occasionally need to call a WDM service from a VxD. The Windows 98 DDK
has some limited support for doing this, although it isn't fully
documented.
In subdirectory lib \ i386 \ free \ win98 you'll find library wdmvxd.clb. This
library gives you linkage to most if not all of the WDM entry points
provided with Windows 98. Each of the object files loads registers and
invokes INT 2Eh, which traps to a system dispatcher. Before invoking the
called WDM service, the dispatcher takes care of ensuring that the
stack is set up for structured excepTIon handling, which is supported in
WDM drivers.
The library is set up to look like an import library, even though it
does not result in any imports being generated. If you use DUMPBIN
with the / linkermember switch, you'll see that the entry points are
prefixed with __imp_. This was done so that you can use prototypes
directly from wdm.h.
For example, suppose you wanted to call RtlInitUnicodeString from a VxD.
You would need this prototype from wdm.h:
NTSYSAPI
VOID
NTAPI
RtlInitUnicodeString (
PUNICODE_STRING DesTInaTIonString,
PCWSTR SourceString
);
In addiTIon, you may need these definitions:
#define NTSYSAPI __declspec (dllimport)
#define NTAPI __stdcall
Then it's simply a matter of having the typedef's and linking against
wdmvxd.clb.
Use wdmvxd.clb only when absolutely necessary, and always with extreme
caution. Because IRQL is largely undefined in VxDs, there are numerous
ways to get into trouble when making these calls.
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