Problem while mapping Kernel memory to User memory

• Subject: Problem while mapping Kernel memory to User memory
• From: "amber maheshwari" <email@hidden>
• Date: Wed, 16 May 2007 17:26:39 +0530
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Dear All,

 
My machine configuration: Mac OS X 10.4.9 , G4

I need to map my kernel's virtual memory at user level, but not able to achieve it. Below are the steps performed:

I am using IOConnectMapMemory call  to get the kernel memory  at the user level. But at user space I am only able to get the first address of that memory segment (which is mapped using getVirtualAddress() in the driver). At kernel level I have full access of this memory But I am not able to map it properly at the user level.

USER LEVEL:

At user level I am using following code :

    /* code snippet */

    vm_address_t        address = nil;   

       io_connect_t   dataPort= 0;

    kernResult = IOServiceOpen(serviceObject, mach_task_self(), 0, &dataPort);

   // Release the io_service_t now that we're done with it.

    IOObjectRelease(serviceObject);

    if (kernResult != KERN_SUCCESS)

    {

        //printf("IOServiceOpen returned %d\n", kernResult);

        return 0;

    }

     // IOConnectMapMemory will call clientMemoryForType() inside your user client class.

    printf("\nsize initially = %d\n",size);

    kernResult = IOConnectMapMemory(dataPort, kIODefaultMemoryType, mach_task_self(), &address, &size, kIOMapAnywhere);

    this call IOConnectMapMemory is successful.

KERNEL LEVEL:

In the User Client of driver I have implemented clientMemoryForType method in the following way:

IOReturn

    drv_user::clientMemoryForType(UInt32 type, IOOptionBits * options, IOMemoryDescriptor ** memory)

{

    IOReturn result = kIOReturnSuccess;

    fMemoryToShare = IOMemoryDescriptor::withAddress( (vm_address_t)deviceRegisters, //virtual address of the first byte in memory

                                                sizeof(SDA_reg),

                                                kIODirectionOut,

                                                fTask);

    if ( fMemoryToShare == NULL )

    {

    IOLog("\nError! memDescOut is null\n");

    return kIOReturnNoResources;

    }

    fMemoryToShare->retain();

    *memory = fMemoryToShare;

     IOLog("\nSuccess!, nclientMemoryForType complete... \n");

    return result;

}

 
Where

typedef struct SDA_reg {

    UInt8      reg[0x10000];   

    UInt8   reg1;

    UInt8   reg2; 

 } SDA_reg;

SDA_reg   *     deviceRegisters;

deviceRegisters  = (SDA_reg *)fRegisterMap->getVirtualAddress();//Getting virtual address in the start method of Driver

Can anybody suggest any solution or can tell about wether my approach is wrong or some function parameter is incorrect.

Any relevant code snippet will also be of great help.

Thanks in Advance,

Amber 

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