ioperm() with ports above 0x3ff

Andrew Dyer
Tue Feb 19 00:58:00 GMT 2008

I am having problems using ioperm() to try and access a parallel printer port on
a PCI card in my system running WinXP.  The port is mapped to I/O port address
0xDCD8.  I cannot access the port because the ioperm() driver has a check to
limit I/O port accesses to < 0x400.

from /usr/src/ioperm-0.4/driver/ioperm.c, lines 95-100

		/* test input buffer size and parameters */
		if ((io_stack->Parameters.DeviceIoControl.InputBufferLength < sizeof (struct
			|| (!ioperm_data) || (ioperm_data->from + ioperm_data->num > 0x400))
		} else {

It looks like there is complete support for the bitmap that NT uses to allow I/O
permissions across a full x86 I/O port range of 0-0xFFFF, but the library
enforces this artificial port limit check.  Is there a reason I can't see for
having this restrictive check in the driver (especially considering the nature
of what the driver does)?  

I can't rebuild the driver as I don't have access to the DDK.  Can someone
rebuild it with the check modified so I could test it?

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