python - tuntap 的替代品

Question

我正在尝试通过连接到我的计算机(特别是 USRP)的 radio 传输 TCP/IP。现在，使用 Tun/Tap 设置新的网络接口(interface)非常简单。这是代码:

    from gnuradio import gr, gru, modulation_utils
from gnuradio import usrp
from gnuradio import eng_notation
from gnuradio.eng_option import eng_option
from optparse import OptionParser

import random
import time
import struct
import sys
import os

# from current dir
from transmit_path import transmit_path
from receive_path import receive_path
import fusb_options

#print os.getpid()
#raw_input('Attach and press enter')

# Linux specific...
# TUNSETIFF ifr flags from <linux/tun_if.h>

IFF_TUN     = 0x0001   # tunnel IP packets
IFF_TAP     = 0x0002   # tunnel ethernet frames
IFF_NO_PI   = 0x1000   # don't pass extra packet info
IFF_ONE_QUEUE   = 0x2000   # beats me ;)

def open_tun_interface(tun_device_filename):
    from fcntl import ioctl

    mode = IFF_TAP | IFF_NO_PI
    TUNSETIFF = 0x400454ca

    tun = os.open(tun_device_filename, os.O_RDWR)
    ifs = ioctl(tun, TUNSETIFF, struct.pack("16sH", "gr%d", mode))
    ifname = ifs[:16].strip("\x00")
    return (tun, ifname)


# /////////////////////////////////////////////////////////////////////////////
#                             the flow graph
# /////////////////////////////////////////////////////////////////////////////

class my_top_block(gr.top_block):

    def __init__(self, mod_class, demod_class,
                 rx_callback, options):

        gr.top_block.__init__(self)
        self.txpath = transmit_path(mod_class, options)
        self.rxpath = receive_path(demod_class, rx_callback, options)
    self.connect(self.txpath);
    self.connect(self.rxpath);

    def send_pkt(self, payload='', eof=False):
        return self.txpath.send_pkt(payload, eof)

    def carrier_sensed(self):
        """
        Return True if the receive path thinks there's carrier
        """
        return self.rxpath.carrier_sensed()


# /////////////////////////////////////////////////////////////////////////////
#                           Carrier Sense MAC
# /////////////////////////////////////////////////////////////////////////////

class cs_mac(object):
    """
    Prototype carrier sense MAC

    Reads packets from the TUN/TAP interface, and sends them to the PHY.
    Receives packets from the PHY via phy_rx_callback, and sends them
    into the TUN/TAP interface.

    Of course, we're not restricted to getting packets via TUN/TAP, this
    is just an example.
    """
    def __init__(self, tun_fd, verbose=False):
        self.tun_fd = tun_fd       # file descriptor for TUN/TAP interface
        self.verbose = verbose
        self.tb = None             # top block (access to PHY)

    def set_top_block(self, tb):
        self.tb = tb

    def phy_rx_callback(self, ok, payload):
        """
        Invoked by thread associated with PHY to pass received packet up.

        @param ok: bool indicating whether payload CRC was OK
        @param payload: contents of the packet (string)
        """
        if self.verbose:
            print "Rx: ok = %r  len(payload) = %4d" % (ok, len(payload))
        if ok:
            os.write(self.tun_fd, payload)

    def main_loop(self):
        """
        Main loop for MAC.
        Only returns if we get an error reading from TUN.

        FIXME: may want to check for EINTR and EAGAIN and reissue read
        """
        min_delay = 0.001               # seconds

        while 1:
            payload = os.read(self.tun_fd, 10*1024)
            if not payload:
                self.tb.send_pkt(eof=True)
                break

            if self.verbose:
                print "Tx: len(payload) = %4d" % (len(payload),)

            delay = min_delay
            while self.tb.carrier_sensed():
                sys.stderr.write('B')
                time.sleep(delay)
                if delay < 0.050:
                    delay = delay * 2       # exponential back-off

            self.tb.send_pkt(payload)


# /////////////////////////////////////////////////////////////////////////////
#                                   main
# /////////////////////////////////////////////////////////////////////////////

def main():

    mods = modulation_utils.type_1_mods()
    demods = modulation_utils.type_1_demods()

    parser = OptionParser (option_class=eng_option, conflict_handler="resolve")
    expert_grp = parser.add_option_group("Expert")

    parser.add_option("-m", "--modulation", type="choice", choices=mods.keys(),
                      default='gmsk',
                      help="Select modulation from: %s [default=%%default]"
                            % (', '.join(mods.keys()),))

    parser.add_option("-v","--verbose", action="store_true", default=False)
    expert_grp.add_option("-c", "--carrier-threshold", type="eng_float", default=30,
                          help="set carrier detect threshold (dB) [default=%default]")
    expert_grp.add_option("","--tun-device-filename", default="/dev/net/tun",
                          help="path to tun device file [default=%default]")

    transmit_path.add_options(parser, expert_grp)
    receive_path.add_options(parser, expert_grp)

    for mod in mods.values():
        mod.add_options(expert_grp)

    for demod in demods.values():
        demod.add_options(expert_grp)

    fusb_options.add_options(expert_grp)

    (options, args) = parser.parse_args ()
    if len(args) != 0:
        parser.print_help(sys.stderr)
        sys.exit(1)

    if options.rx_freq is None or options.tx_freq is None:
        sys.stderr.write("You must specify -f FREQ or --freq FREQ\n")
        parser.print_help(sys.stderr)
        sys.exit(1)

    # open the TUN/TAP interface
    (tun_fd, tun_ifname) = open_tun_interface(options.tun_device_filename)

    # Attempt to enable realtime scheduling
    r = gr.enable_realtime_scheduling()
    if r == gr.RT_OK:
        realtime = True
    else:
        realtime = False
        print "Note: failed to enable realtime scheduling"


    # If the user hasn't set the fusb_* parameters on the command line,
    # pick some values that will reduce latency.

    if options.fusb_block_size == 0 and options.fusb_nblocks == 0:
        if realtime:                        # be more aggressive
            options.fusb_block_size = gr.prefs().get_long('fusb', 'rt_block_size', 1024)
            options.fusb_nblocks    = gr.prefs().get_long('fusb', 'rt_nblocks', 16)
        else:
            options.fusb_block_size = gr.prefs().get_long('fusb', 'block_size', 4096)
            options.fusb_nblocks    = gr.prefs().get_long('fusb', 'nblocks', 16)

    #print "fusb_block_size =", options.fusb_block_size
    #print "fusb_nblocks    =", options.fusb_nblocks

    # instantiate the MAC
    mac = cs_mac(tun_fd, verbose=True)


    # build the graph (PHY)
    tb = my_top_block(mods[options.modulation],
                      demods[options.modulation],
                      mac.phy_rx_callback,
                      options)

    mac.set_top_block(tb)    # give the MAC a handle for the PHY

    if tb.txpath.bitrate() != tb.rxpath.bitrate():
        print "WARNING: Transmit bitrate = %sb/sec, Receive bitrate = %sb/sec" % (
            eng_notation.num_to_str(tb.txpath.bitrate()),
            eng_notation.num_to_str(tb.rxpath.bitrate()))

    print "modulation:     %s"   % (options.modulation,)
    print "freq:           %s"      % (eng_notation.num_to_str(options.tx_freq))
    print "bitrate:        %sb/sec" % (eng_notation.num_to_str(tb.txpath.bitrate()),)
    print "samples/symbol: %3d" % (tb.txpath.samples_per_symbol(),)
    #print "interp:         %3d" % (tb.txpath.interp(),)
    #print "decim:          %3d" % (tb.rxpath.decim(),)

    tb.rxpath.set_carrier_threshold(options.carrier_threshold)
    print "Carrier sense threshold:", options.carrier_threshold, "dB"

    print
    print "Allocated virtual ethernet interface: %s" % (tun_ifname,)
    print "You must now use ifconfig to set its IP address. E.g.,"
    print
    print "  $ sudo ifconfig %s 192.168.200.1" % (tun_ifname,)
    print
    print "Be sure to use a different address in the same subnet for each machine."
    print


    tb.start()    # Start executing the flow graph (runs in separate threads)

    mac.main_loop()    # don't expect this to return...

    tb.stop()     # but if it does, tell flow graph to stop.
    tb.wait()     # wait for it to finish


if __name__ == '__main__':
    try:
        main()
    except KeyboardInterrupt:
        pass

(任何熟悉 GNU Radio 的人都会认出这是 tunnel.py) 我的问题是，是否有比 tun/tap 更好的方法将数据包移入和移出内核？我一直在看 ipip 或者可能使用套接字，但我很确定那些不会很快。速度是我最关心的。

Answer 1

请记住，tunnel.py 是一个非常非常粗略的示例，并且已经有一段时间没有更新了。它并不是真的要成为其他代码的基础，因此请注意您对代码的依赖程度。

此外，请记住，不可靠 radio 链路上的 TCP 存在重大问题: http://en.wikipedia.org/wiki/Transmission_Control_Protocol#TCP_over_wireless_networks