deviceiocontrol string format

Dear All,

I am new to python win32, and i cannot figure out how to
format the data 
string for deviceiocontrol code with win32file.

I have the following c struct in my driver file:
typedef struct _WRITE_DEVICE_DATA_INPARAMS
{
	UCHAR ucMemorySpace;		// 0: I/O Space, 1: Mem Space.
	ULONG ulPhysicalAddress;	// Dword-aligned offset to write
to.
	ULONG ulItemSize;			// 1: Byte, 2: Word, 4: Dword.
	ULONG ulItemCount;			// Number of bytes, words or dwords.

	union{
		UCHAR vucDataBuf[1];
		USHORT vusDataBuf[1];
		ULONG vulDataBuf[1];
	}data;

}WRITE_DEVICE_DATA_INPARAMS, *PWRITE_DEVICE_DATA_INPARAMS;

I tried to format my data string like this:
data=struct.pack('BLLLH',2,1020,2,1,0)

but got the following error:
OverflowError: long int too large to convert to int

Apparentely the error is coming from 1020. However it is
define as ulong 
for both case the c struct and the python struct.pack.

Thanks in advance for your help

Regards
Brice
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On 26/05/2006 4:43 AM, B.P.S.Thurincity.ac.uk wrote:
> Dear All,
> 
> I am new to python win32, and i cannot figure out how
to format the data 
> string for deviceiocontrol code with win32file.
> 
> I have the following c struct in my driver file:
> typedef struct _WRITE_DEVICE_DATA_INPARAMS
> {
> 	UCHAR ucMemorySpace;		// 0: I/O Space, 1: Mem Space.
> 	ULONG ulPhysicalAddress;	// Dword-aligned offset to
write to.
> 	ULONG ulItemSize;			// 1: Byte, 2: Word, 4: Dword.
> 	ULONG ulItemCount;			// Number of bytes, words or
dwords.
> 
> 	union{
> 		UCHAR vucDataBuf[1];
> 		USHORT vusDataBuf[1];
> 		ULONG vulDataBuf[1];
> 	}data;
> 
> }WRITE_DEVICE_DATA_INPARAMS,
*PWRITE_DEVICE_DATA_INPARAMS;
> 
> I tried to format my data string like this:
> data=struct.pack('BLLLH',2,1020,2,1,0)
> 
> but got the following error:
> OverflowError: long int too large to convert to int

It would help if you showed the code that you actually
executed and the 
traceback.

There is no problem with the above pack call:

Python 2.4.2 (#67, Sep 28 2005, 12:41:11) [MSC v.1310 32 bit
(Intel)] on 
win32
Type "help", "copyright",
"credits" or "license" for more
information.
 >>> import struct
 >>> data=struct.pack('BLLLH',2,1020,2,1,0)
 >>> data
'\x02\x00\x00\x00\xfc\x03\x00\x00\x02\x00\x00\x
00\x01\x00\x00\x00\x00\x00'
 >>> hex(1020)
'0x3fc'


Perhaps you meant that the error is coming from
deviceiocontrol.

You will notice that the first item is padded out with 3
bytes of \x00 
so that the 2nd item is aligned on a 32-bit boundary. This
may be the 
cause of your problem. The error that you got is consistent
with 
something trying to convert (positive) 0xFC000000L to a
*signed* 32-bit 
integer. Why signed, I don't know.

What does &(mystruct.ulPhysicalAddress) -
&(mystruct.ucMemorySpace)
[warning: my C is a little rusty!]
give you in C (using the compiler used for the driver)?

If the answer is 1, you need to lose the padding; read the
fine print at 
the end of the struct.pack manual section. Note that the
default 
alignment used is according to the C compiler used to
compile Python 
(Microsoft), which may differ from the alignment used by the
compiler 
used for the driver (gcc?).

If the answer is 4, then the problem is not with your usage
of struct.pack.

> 
> Apparentely the error is coming from 1020. However it
is define as ulong 
> for both case the c struct and the python struct.pack.
> 


HTH,
John
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