IOStorage synchronous write routine crashing

5 Jul 2005

      site_archiver@lists.apple.com
Delivered-To: darwin-kernel@lists.apple.com

Hi Folks,

I am using a synchronous write call in filter scheme driver.

I have created a IOMemoryDescriptor buffer by calling withAddress
function and pass this buffer to the sync write call, but i am getting
crash when this write routine gets called.

My code snippet for the same is as follows:

void com_My_driver::write(IOService* provider,
                                UInt64 byteStart,
                                IOMemoryDescriptor* buffer,
                                IOStorageCompletion completion)

{
    // Allocate a buffer to write the data on disk.
    UInt32 WriteBufSize = 512;

    char * bufWrite = new char[512];
    strcpy(bufWrite, "DRIVER ON MACOS X");

    // Create memory descriptor for the buffer
    IOMemoryDescriptor *WriteBuffer = NULL;

    WriteBuffer = IOMemoryDescriptor::withAddress((void*) bufWrite,
			(IOByteCount) WriteBufSize, kIODirectionOut);

    if(WriteBuffer)
    {
	filteredMedia->write(this, 512, WriteBuffer);  /* crashing just
							here and getting 							memory 	access 							exception*/
    }
    else
    {
        WriteBuffer->release();
        WriteBuffer = 0;
    }

Is it i am missing something while using the sync write call?

I am able to make the code work if I do memory allocations in User
Client and successfully do the write() on disk. But not able to do the
same if I don’t use user client and do allocation in filter scheme
driver.

I think I am not using memory management functions correctly. Is there
any documentation available,how to use IOMemoryDescriptor
in kernel level drivers? I have read KernelProgramming.pdf,
WritingDeviceDrivers.pdf but I didn’t find it useful in my case.

Look forward to pointers so that I can solve this issue.

Thanks in advance,
Yogesh Pahilwan

 _______________________________________________
Do not post admin requests to the list. They will be ignored.
Darwin-kernel mailing list      (Darwin-kernel@lists.apple.com)
Help/Unsubscribe/Update your Subscription:
http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.a...

This email sent to site_archiver@lists.apple.com