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Problem in sending data between User Space & Kernel Space

Hi ALL,

          I'm creating an application which has user space as well as kernel space.I'm using ioctl command to send the data from user space to kernel space.

/////////////////////////////////////////////////////////////////////////////////////////////////////////////
IOCTL Command args structure
/////////////////////////////////////////////////////////////////////////////////////////////////////////////
 typedef struct {
    int len;
    char* data;
} data_struct;

/////////////////////////////////////////////////////////////////////////////////////////////////////////////
KERNEL SPACE CODE
/////////////////////////////////////////////////////////////////////////////////////////////////////////////
int fp_ioctl(dev_t dev, u_long cmd, caddr_t arg,int fflag, struct proc *p)
{
    printf("fp_ioctl called\n");

    data_struct *mdata = (data_struct*) arg;
   
    if (!mdata) {
        printf("mdata is null!\n");
        return 0;
    }
   
    int fd = mdata->len;
    printf("received mdata fd [%d]\n", fd);
    printf("received mdata data [%u]\n", mdata->data);

    char *kerndata  = OSMalloc( (sizeof(char) * fd) + 1, gMallocTag);

    if ( kerndata == NULL )
        printf("Unable to allocate memory for kerndata -----\n");
     
//    int res = copyin((void *)mdata->data, (void *)kerndata, fd);
    size_t done = 0;
    int res = copyinstr((void *)mdata->data, (void *)kerndata,fd, &done);
   
    printf("kerndata -----[%s]\n", kerndata);
    printf("size_t done -----[%d]\n", done);
   
    if ( kerndata )
        OSFree(kerndata, (sizeof(char) * fd) + 1, gMallocTag);
       
    return 0;
}   

/////////////////////////////////////////////////////////////////////////////////////////////////////////////
USER SPACE CODE
/////////////////////////////////////////////////////////////////////////////////////////////////////////////

int sendioctl(char *filename) {
    int result;
    int handle;
   
    char *rootDir = "/";
    if (filename[0] ==0) filename = rootDir;
   
    printf("do hook of [%s]\n",filename);
   
    result = OpenDriver(&handle);
    if (result) {
        return -1;
    }
   
    int fileDesc=open(filename,O_RDONLY);
    if (fileDesc<0) return 4;
    printf("fileDesc is [%d]\n", fileDesc);
   
    data_struct mdata;
    char str[40]= "Hello World  xcbxcbvxcbvcxbcvbcbxxcc456\0";
    int len = strlen(str);
   
    // Create Char * Memory
    mdata.data ="" (char *) malloc ( sizeof(char) * len );
   
    if ( mdata.data == NULL)
        return -12345;
    // Fill Char * Memory with zeros
    memset(mdata.data,0,len);
    // Copy Str to  Char *
    memcpy(mdata.data,str,len);
   
    mdata.len=len;
       
    printf("sending mdata fd [%d]\n", mdata.len);
    printf("sending mdata data [%u]\n", mdata.data );
    printf("sending mdata data [%s]\n", mdata.data );
    printf("sending mdata strlen [%d]\n", strlen(mdata.data));
       
    unsigned long id = FILE_DATA_STRUCT_COMMAND;
    result = ioctl(handle, id, (char*) &mdata);
    printf("first ioctl call result is [%d]. Sleeping for 5 secs..\n", result);

   
    if ( mdata.data != NULL )
        free(mdata.data);


    CloseDriver(handle);
    printf("CloseDriver\n");
   
    close(fileDesc);
    printf("closed first file\n", result);

    return result;
}


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