// [VAtoKA]
//
// convert a user process virtual address (from the current process)
// into a kernel-usable address.  only valid for one page, need to
// call again for next page.
//
// second argument is whether or not the page found will be written.
//
// return 0 on failure.  (at the moment, all failures generate fatal
// exceptions which will kill the process.)
//
// note: this argument takes and returns ints, but we're really
// dealing with addresses.  ints and addresses are both 4 bytes here.
// i'd rather be using void* but this is consistent with the rest of
// nachos.
//
int VAtoKA(int vAddr, bool writing)
{
        int pAddr; // physical address, offset into main memory
        int kAddr; // kernel address, usable from within nachos
        ExceptionType exc;

        DEBUG('a', "VAtoKA conversion for 0x%x\n", vAddr);

        // keep translating until we succeed or raise a fatal exception.
        // a bug in exception handling may turn this into an infinite loop!
        while((exc = Translate(vAddr, &pAddr, 1, writing)) != NoException)
                machine->RaiseException(exc, vAddr);

        // convert the physical offset into a usable pointer
        kAddr = (int)&(machine->mainMemory[pAddr]);
        return kAddr;
}