Problem for read routine in filter scheme driver

9 Jun 2005

      site_archiver@lists.apple.com
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Hi folks,

I have written a filter scheme driver. By using this driver i am able to
write on the disk.But when i call the read API of driver it is returning
me some garbage characters.When i "dd" on the disk i get the correct
buffer that i write on the disk using write routine of driver.

The code snippet for the my read routine is as follows:

void com_My_driver::read(IOService* provider,UInt64 byteStart,
			IOMemoryDescriptor* buffer,
                        IOStorageCompletion completion)
{
    IOLog("\n com_CoreSnap_driver --- read function Called ...\n");

    int i;
    IOByteCount readBytes = 0;
    IOByteCount bufLength = buffer->getLength();
    IOLog("\n bufLength = %lu\n", bufLength);
    char *myBuff1 = new char[bufLength];

    IOLog("\n before read function Called ...\n");
    getProvider()->read(this, byteStart, buffer, completion);
    IOLog("\n After read function Called ...\n");

    IOLog("\n before readbytes function Called ...\n");
    readBytes = buffer->readBytes(0, myBuff1, bufLength);
    IOLog("\n before readbytes function Called ...\n");

    IOLog("\n Calling for loop After read .....\n");

    for (i = 0; i < 8192; i++)
    {
        IOLog("%c C", *myBuff1);
    }

    IOLog("\n For loop overs After read.....\n");
}

My for loop IOLog shows the following output:

Jun  9 21:44:32 localhost kernel:
Jun  9 21:44:32 localhost kernel: com_My_driver --- handleIsOpen
function Called
Jun  9 21:44:32 localhost kernel:
com_My_driver[0x11be680]::handleIsOpen(0x191e200)
Jun  9 21:44:32 localhost kernel:
Jun  9 21:44:32 localhost kernel: com_My_driver --- handleClose function
Called
Jun  9 21:44:32 localhost kernel:
com_My_driver[0x11be680]::handleClose(0x191e200, 0)
Jun  9 21:44:39 localhost kernel: C CCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
CCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCC
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCC CCCCCCCCCCCCC
Jun  9 21:44:39 localhost kernel: For loop overs After read.....

It shows the garbage values.I think it will have to show the buffer
which gets write on the disk.

Am i missing something in my read?
Please suggest.

Thanks in advance,
Yogesh
~

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Problem for read routine in filter scheme driver

Yogesh P