NVX: netmap loop

While migrating the Ueberschall accelerator code here, I stumbled over some sketch code that is worth keeping back to some day.

c = 0
stats = {}


def start(app):
    # set inbox/outbox to first configured RX/TX queue (eg from a NIC or an NVMe)
    app.inbox.append(app.rx[0].queue)
    app.outbox.append(app.tx[0].queue)

    # start looping with freq capped to 100 Hz (or 10 ms period)
    app.loop(100)

def loop(app):
    # process incoming message (mbuf) queued in inbox
    for msg in app.inbox:

        # msg is a mbuf instance
        n = len(msg)

        # stopping the app with error
        if n > 1000:
            app.stop(Exception(u'msg too long! stopping'.encode()))

        # loop can keep state from outer scope
        if n not in stats:
            stats[n] = 0
        stats[n] += 1

        # mbuf handling
        msg2 = msg.duplicate()
        msg2.write(20, b'hello')

        # queue outgoing message (mbuf) in outbox
        app.outbox.send(msg2)

        # stopping the app with success, returning a result
        if c > 10000:
            result = {u'total': c, u'stat': stats}
            app.stop(result)

def stop(app):
    # stop or restart the app
    if app.err:
        print('unexpected error - exciting', app.err)
    else:
        # restart the app
        app.start()

Start by searching the repository for NVX, netmap, Ueberschall, and the app.inbox/app.outbox loop concepts shown in the issue. The issue contains only exploratory Python sketch code; work is not well-defined until the project identifies an entry point, intended behavior, and acceptance criteria.