/**
* Transfer data from the specified array to this process's virtual memory. This method handles
* address translation details. This method must <i>not</i> destroy the current process if an
* error occurs, but instead should return the number of bytes successfully copied (or zero if no
* data could be copied).
*
* @param vaddr the first byte of virtual memory to write.
* @param data the array containing the data to transfer.
* @param offset the first byte to transfer from the array.
* @param length the number of bytes to transfer from the array to virtual memory.
* @return the number of bytes successfully transferred.
*/
public int writeVirtualMemory(int vaddr, byte[] data, int offset, int length) {
Lib.assertTrue(offset >= 0 && length >= 0 && offset + length <= data.length);
byte[] memory = Machine.processor().getMemory();
int transferred = 0;
while (length > 0 && offset < data.length) {
int addrOffset = vaddr % 1024;
int virtualPage = vaddr / 1024;
if (virtualPage >= pageTable.length || virtualPage < 0) {
break;
}
TranslationEntry pte = pageTable[virtualPage];
if (!pte.valid || pte.readOnly) {
break;
}
pte.used = true;
pte.dirty = true;
int physPage = pte.ppn;
int physAddr = physPage * 1024 + addrOffset;
int transferLength = Math.min(data.length - offset, Math.min(length, 1024 - addrOffset));
System.arraycopy(data, offset, memory, physAddr, transferLength);
vaddr += transferLength;
offset += transferLength;
length -= transferLength;
transferred += transferLength;
}
return transferred;
}
private int handleWrite(int a0, int bufaddr, int count) {
OpenFile file = openfiles.get(a0);
if (file == null) return -1;
byte[] transfer_buffer = new byte[Processor.pageSize];
int total_transfer = 0;
while (count > 0) {
int readlen = Math.min(Processor.pageSize, count);
int actualread = readVirtualMemory(bufaddr, transfer_buffer, 0, readlen);
if (actualread == -1) return -1;
if (actualread < readlen) return -1;
int written_bytes = file.write(transfer_buffer, 0, actualread);
if (written_bytes != actualread) {
return -1;
}
count -= actualread;
bufaddr += actualread;
total_transfer += actualread;
}
return total_transfer;
}