ULONG
MmGetMdlByteCount(
IN PMDL Mdl
);
MmGetMdlByteCount returns the length in bytes of the buffer described by a given MDL.
MmGetMdlByteCount returns the byte count of the buffer described by Mdl.
Callers of MmGetMdlByteCount can be running at any IRQL. Usually, callers are running at IRQL <= DISPATCH_LEVEL.