IO.H

The public symbol file NTKRPAMP.PDB for the original release of Windows 10 tells that the kernel is built with the IO.H header at

d:\th\minkernel\ntos\inc

and draws from it the following type definition:

Line Number Type
51 struct _DUMP_STACK_CONTEXT
264 struct _IO_TIMER
277 struct _IO_CLIENT_EXTENSION

The header IO.H is not known in any Device Driver Kit (DDK) or Windows Driver Kit (WDK).