Re: passing buffer from User Client to Driver

18 Apr 2005

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A few points,
Godfrey
On 04/18/2005, at 6:32 , Imran wrote:
Dear All,
My code snippet is as follows:
My UserKernelShared.h contains following structure -
typedef struct  MySampleStruct
{
    UInt32 size;
    char buff [kBufSize];
} MySampleStruct;
// these are the User Client method names
enum
{
    kMyUserClientOpen,
    kMyUserClientClose,
    kMyDoWrite,
    kMyDoRead
    kMyDoReadWrite,
    kMyNumberOfMethods
};
My UserSpace.c includes following call -
In main()
{
    kernResult = MyDoWrite(dataPort);                 /*declaration*/
      if (kernResult != KERN_SUCCESS)
    {
        printf("\n kMyDoWrite returned %d\n", kernResult);
            fflush(stdout);
    }
}
/*Definition for MyDoWrite() in userspace application*/
static kern_return_t
MyDoWrite(io_connect_t connect)
{
    kern_return_t    kernResult;
    MySampleStruct   sampleStructIn;
    MySampleStruct   sampleStructOut;
    strcpy(sampleStructIn.buff,"MACOSX Write Call");
    UInt32 size;
    size = kBufSize;
    sampleStructIn.size = size;
    IOByteCount structSizeIn = sizeof(MySampleStruct);
    IOByteCount structSizeOut = sizeof(MySampleStruct);
My UserClient.h includes -
class com_MySoftwareCompany_MyUserClient : public IOUserClient
{
    OSDeclareDefaultStructors(com_MySoftwareCompany_MyUserClient)
protected:
    IOService*            fProvider;
    com_MySoftwareCompany_driver_MyFilterScheme* UCProvider;
    task_t            fTask;
    bool            fDead;
public:
     //Note - Also includes all IOUserClient Methods
};
My UserClient.cpp includes -
     if (index < (UInt32)kMyNumberOfMethods)
     {
      if(index == kMyUserClientOpen || index == kMyUserClientClose ||
index == kMyDoWrite){
             *target = this;
        }
        else {
              *target = UCProvider;
        }
        return (IOExternalMethod *) &sMethods[index];
    }
    return NULL;
}
IOReturn com_MySoftwareCompany_MyUserClient::myDoWrite(MySampleStruct
*vInStruct, IOByteCount vInStructSize, MySampleStruct *vOutStruct,
IOByteCount * vOutStructSize)
{
    IOReturn retWrite = kIOReturnSuccess;
    char* buf = new char[kBufSize];
    UInt32 Size;
    buf = vInStruct->buff;
    Size = vInStruct->size;
    IOByteCount bufLength = WriteBuffer->getLength();
    if (!WriteBuffer){
        return kIOReturnNoMemory;
    }
    else {
        // wire it and make sure we can read it
            retWrite = WriteBuffer->prepare();
            if(retWrite == kIOReturnSuccess) {
             memMap = WriteBuffer->map();
            if(!memMap) {
                return kIOReturnNoMemory;
            }
            else {
                void* pData = (void*)(memMap->getVirtualAddress());
    delete[] buf;
    return retWrite;
}
    // If the user client's 'open' method was never called, return
kIOReturnNotOpen.
    if (!isOpen()) {
        return kIOReturnNotOpen;
    }
    else {
        IOLog("\n Userclient is open for the driver....\n");
    }
    IOByteCount readBytes;
    UInt64 byteStart = 0;
    IOByteCount bufLength = inBuffer->getLength();
    IOLog("\n bufLength = %lu\n", bufLength);
    char myBuff[512];
    readBytes = inBuffer->readBytes(0, myBuff, bufLength);
    getProvider()->write(this, 512,inBuffer, completion);
    return retDrWrite;
}
Thanks
Imran
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1> Could you change all occurrences of "MySoftwareCompany" to
"spsoftindia", or something else more meaningful.  The problem is
that your driver will fail to load for obscure reasons in the future
if you continue using a generic came like this.
2> The use of the 'v' prefix in arguments is to indicate that the
input type is a void *.  This is immediately cast to the appropriate
type.  I use this idiom to get clean, warning free compiles.  I
suggest changing variables like (vInStruct) to inStruct if you don't
care about the void * cast.
3> You probably don't need to create a map on the memory descriptor.
In fact it is better well more efficient if you don't.
4> Does the 'readBytes' call return the data that you expect to be
there?  Are you call in the 'synchronous' write on your provider?
I got success in all the function required to call for passing
buffer from

User Application to Driver through User Client.

I have use IOMemoryDescriptor for mapping the user space buffer in
kernel

address space.
Still my problem is I am not able to get the buffer in the driver
though I

am able to pass it from user application to User Client successfully.
    if (!connect) {

        printf("\n Unable to make connection in MyDoWrite of userspace

app.....\n");

        return kIOReturnNoDevice;

    }

    else {

       kernResult = IOConnectMethodStructureIStructureO(connect,
kMyDoWrite,

structSizeIn, &structSizeOut,

&sampleStructIn, &sampleStructOut);

    }

    if(kernResult == kIOReturnSuccess){

        printf("\n kMyDoWrite was successful..........\n");

    }

    return kernResult;

}
virtual IOReturn myDoWrite(MySampleStruct *vInStruct, IOByteCount

vInStructSize, MySampleStruct *vOutStruct, IOByteCount
*vOutStructSize);
IOExternalMethod *

com_MySoftwareCompany_MyUserClient::getTargetAndMethodForIndex
(IOService **

target, UInt32 index)

{

    static const IOExternalMethod sMethods[kMyNumberOfMethods] =

    {

       { // kMyDoWrite

            NULL, IOMethod)
&com_MySoftwareCompany_MyUserClient::myDoWrite,

kIOUCStructIStructO,

            sizeof(MySampleStruct), sizeof(MySampleStruct)},

    };
    IOMemoryDescriptor *WriteBuffer = NULL;

    IOMemoryMap *memMap = NULL;

    WriteBuffer = IOMemoryDescriptor::withAddress((vm_address_t)

vInStruct->buff, (IOByteCount) vInStruct->size, kIODirectionOut,
fTask);
                if(pData == NULL) {

                    return kIOReturnError;

                }

                else {

                UCProvider =

OSDynamicCast(com_MySoftwareCompany_driver_MyFilterScheme, fProvider);

                retWrite =

UCProvider->DoDriverWrite(WriteBuffer);  // Calling Driver
DoDriverWrite

Routine

                }

        }

    }

      memMap->unmap();

      memMap->release();

      WriteBuffer->complete();

      WriteBuffer->release();

      WriteBuffer = NULL;
My Driver.cpp includes -

// kMyDoWrite

IOReturn

com_MySoftwareCompany_driver_MyFilterScheme::DoDriverWrite
(IOMemoryDescripto

r * inBuffer)

{

    IOReturn retDrWrite = kIOReturnSuccess;

    IOStorageCompletion completion;
The problem I am facing is that all my IOMemoryDescriptor calls
such as

prepare(), map(), complete() are getting succeeded but the
WriteBuffer which

is a IOMemoryDescriptor pointer I am passing to the DoDriverWrite()
driver

routine

is not getting passed from userclient to driver.

When I print the IOMemoryDescriptor addresses in userclient and
driver it

gives me the same address but when I print the buffer in driver it
shows

nothing but the blank.

Is there anything I am missing for mapping the user space buffer in
kernel

address space???
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Re: passing buffer from User Client to Driver

Godfrey van der Linden