Sample Filter Scheme (read doesn't work)

3 Nov 2004

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Hi,

I'm trying to implement Filter Scheme using "Sample Filter Scheme" from
the Apple's documentation. My driver is successfully loaded, creating a
Volume for the partition I created with hdiutil. At this stage I want just
to process a content of a buffer in my driver's read()/write() methods.
In both methods I allocate a temporary char *myBuff of
IOMemoryDescriptor* buffer->getLength() size, pass it to byffer->readBytes()
and then send myBuff to IOLog() method that prints it to
/var/log/system.log.

It works for getProvider()->write() but it shows also the data which is not
a content of a file.
It DOESN'T work at all for getProvider()->read().

QUESTION 1: Why getProvider()->read() doesn't bring the file data at all?
-------------------------------------------------------------------------
It seems that getProvider()->read() doesn't work, since calling
buffer->readBytes() in read() before (for debug only) and after
getProvider()->read()
gives the same junk in myBuff. What is wrong with my read() method?

QUESTION 2: How can I know what data is read/written with
getProvider()->read/write() ?
----------------------------------------------------------------------------
-----------
IOLog() shows that read/write() receives some strange data which is not
a file content. How can I know what data contains buffer?

Following is the source code of my read() and write() methods.

Any help will be appreciated.
Thanks in advance!

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 - -

void com_MyTutorial_driver_MyFilterscheme::read(IOService* /* client */,
                                                   UInt64 byteStart,
                                                   IOMemoryDescriptor*
buffer,
                                                   IOStorageCompletion
completion)
{

	IOByteCount readBytes;
	IOByteCount bufLength = buffer->getLength();
	char *myBuff = new char[bufLength];

	readBytes = buffer->readBytes(0, myBuff, bufLength);
	IOLog("MyFilterscheme::read BEFORE*** readBytes = %lu  byteStart = %lu
bufLength = %lu  buffer = %s ***\n",
			(long)readBytes, (long)byteStart, (long)bufLength, myBuff);

    getProvider()->read(this, byteStart, buffer, completion);

	readBytes = buffer->readBytes(0, myBuff, bufLength);

	for (IOByteCount i = 0; i < bufLength - 1; i++)
	{
		if (myBuff [i] == 't')
			if (myBuff [i+1] == 'e')
				IOLog("MyFilterscheme::read ***FOUND*** buffer @ %lu = %s ***\n",
					(long)i, myBuff + i);
	}

	IOLog("MyFilterscheme::read AFTER *** readBytes = %lu  byteStart = %lu
bufLength = %lu  buffer = %s ***\n",
			(long)readBytes, (long)byteStart, (long)bufLength, myBuff);

	delete[] myBuff;
}

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 - -

void com_MyTutorial_driver_MyFilterscheme::write(IOService* /* client */,
                                                    UInt64 byteStart,
                                                    IOMemoryDescriptor*
buffer,
                                                    IOStorageCompletion
completion)
{
	IOByteCount readBytes;
	IOByteCount bufLength = buffer->getLength();
	char *myBuff = new char[bufLength];
	readBytes = buffer->readBytes(0, myBuff, bufLength);

	IOLog("MyFilterscheme::write  readBytes = %lu  byteStart = %lu  bufLength =
%lu  buffer = %s ***\n",
			(long)readBytes, (long)byteStart, (long)bufLength, myBuff);

    getProvider()->write(this, byteStart, buffer, completion);

	delete[] myBuff;
}

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Sample Filter Scheme (read doesn't work)

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