vmprocess.java

Nachos 5 java version

package nachos.vm;

import nachos.machine.*;
import nachos.threads.*;
import nachos.userprog.*;
import nachos.vm.*;

/**
 * A <tt>UserProcess</tt> that supports demand-paging.
 */
public class VMProcess extends UserProcess {
    /**
     * Allocate a new process.
     */
    public VMProcess() {
	super();
    }

    /**
     * Save the state of this process in preparation for a context switch.
     * Called by <tt>UThread.saveState()</tt>.
     */
    public void saveState() {
	super.saveState();
    }

    /**
     * Restore the state of this process after a context switch. Called by
     * <tt>UThread.restoreState()</tt>.
     */
    public void restoreState() {
	super.restoreState();
    }

    /**
     * Initializes page tables for this process so that the executable can be
     * demand-paged.
     *
     * @return	<tt>true</tt> if successful.
     */
    protected boolean loadSections() {
	return super.loadSections();
    }

    /**
     * Release any resources allocated by <tt>loadSections()</tt>.
     */
    protected void unloadSections() {
	super.unloadSections();
    }    

    private static final int
	syscallMmap = 10;
    
    /**
     * Handle a syscall exception. Called by <tt>handleException()</tt>. The
     * <i>syscall</i> argument identifies which syscall the user executed:
     *
     * <table>
     * <tr><td>syscall#</td><td>syscall prototype</td></tr>
     * <tr><td>10</td><td><tt>int  mmap(int fd, char *address);</tt></td></tr>
     * </table>
     * 
     * @param	syscall	the syscall number.
     * @param	a0	the first syscall argument.
     * @param	a1	the second syscall argument.
     * @param	a2	the third syscall argument.
     * @param	a3	the fourth syscall argument.
     * @return	the value to be returned to the user.
     */
    public int handleSyscall(int syscall, int a0, int a1, int a2, int a3) {
	switch (syscall) {
	default:
	    return super.handleSyscall(syscall, a0, a1, a2, a3);
	}
    }

    /**
     * Handle a user exception. Called by
     * <tt>UserKernel.exceptionHandler()</tt>. The
     * <i>cause</i> argument identifies which exception occurred; see the
     * <tt>Processor.exceptionZZZ</tt> constants.
     *
     * @param	cause	the user exception that occurred.
     */
    public void handleException(int cause) {
	Processor processor = Machine.processor();

	switch (cause) {
	default:
	    super.handleException(cause);
	    break;
	}
    }
	
    private static final int pageSize = Processor.pageSize;
    private static final char dbgProcess = 'a';
}