Writing to disk using filter scheme driver

30 Mar 2005

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Hi folks,
I have written a filter scheme driver,userclient and userspace
application tool for doing read/write operations on IOMedia partitions.

I have successfully send a structure from userspace to kernelspace
through userclient.But when i try to read/write a buffer from userspace
to kernel space,i am not able to map userspace buffer to kernel address
space.
I am specifying my code here.
UserkernelShared.h includes the following structure.
typedef struct  MySampleStruct
{ UInt32 size;
  void* buff;
} MySampleStruct;
In main function of userspace application i am calling the SPSOFT_Write
function as follows.
char    *buf;
UInt32  size;
size = kBufSize;
buf = malloc(sizeof(char) * 1024);
bzero(buf, sizeof(char) * 1048576);
strcpy(buf, " Hello MACOSX");

I want to write this "buf" to the disk through userclient.

// This shows an example of calling a user client's open method.
kernResult = MyDoWrite(dataPort, buf, size);
if (kernResult != KERN_SUCCESS)
{     printf("\n kMyDoWrite returned %d\n", kernResult);
     // This closes the connection to our user client and destroys the
connect handle.
      IOServiceClose(dataPort);
     return 0;
}

The definition of MyDoWrite is as follows.
kern_return_t
MyDoWrite(io_connect_t connect, void *buf, UInt32 size)
{   kern_return_t               kernResult;
    if (!connect){
        return kIOReturnNoDevice;
    }
    else {
        kernResult = IOConnectMethodScalarIStructureI(connect,
                                            kMyDoWrite,
                                            0,
                                            size,
                                            buf
                                            );
    }
    if (kernResult == kIOReturnSuccess){
        printf("\n kMyDoWrite was successful..........\n");
    }
    return kernResult;
}
My Userclient.h and Userclient.cpp includes the following code.

com_MySoftwareCompany_driver_MyFilterScheme*        fProvider;

IOExternalMethod *
com_MySoftwareCompany_MyUserClient::getTargetAndMethodForIndex(IOService
** target, UInt32 index)
{
	{ // kMyDoWrite
             NULL,
            (IOMethod) &com_MySoftwareCompany_MyUserClient::myDoWrite,
            kIOUCScalarIStructI,
            0,
            0xffffffff
        },
}
IOReturn com_MySoftwareCompany_MyUserClient::myDoWrite(void* buf, UInt32
size)
{	IOReturn retWrite = kIOReturnSuccess;
        UInt32 Size = size;
        if (fProvider && !isInactive()){
	 IOMemoryDescriptor *mem = IOMemoryDescriptor::withAddress(buf, 1024,
kIODirectionOut);
            if (mem){
		retWrite = mem->prepare();
                if(kIOReturnSuccess == retWrite){
                    	retWrite = fProvider->myDoWrite(mem,Size); //when i
call this driver function it gives me the error as IOService::fProvider
has no function myDoWrite.
                }
                mem->complete();
                mem->release();
            }else{
		 retWrite = kIOReturnNoMemory;
            }
            release();
        }

How should i call the filter scheme driver read/write routines from my
userclient?? Or is there any sample code of read/write for filter scheme
driver???

Any help, certainly help me in solving this problem.
Thanks in advance.
Yogesh Pahilwan

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