From 36276ba2392f030250fa9dd1e1ea28a026bc51c6 Mon Sep 17 00:00:00 2001 From: Pin-Yen Lin Date: Tue, 14 Aug 2018 14:23:25 +0800 Subject: [PATCH] net: Fix a bug when receiving fragamented packets In the previous implementation, the function EtherTap::recvReal will only read one packet when received some ``interrupt'' (explicitly, when async_IO set to true). When someone tries to send a large message to the simulated device, the message will be divided to several packets due to packet fragmentation. In this situation recvReal will only read one packet and left the other packets in the buffer. This significantly increases the networking latency. So before reading from socket, I change the socket into non-blocking mode and keep reading from it until there's no packet left. Change-Id: Ieb94a8532cd3994862b6f3eb9474caf7ccf617da Reviewed-on: https://gem5-review.googlesource.com/12338 Reviewed-by: Andreas Sandberg Reviewed-by: Jason Lowe-Power Maintainer: Jason Lowe-Power --- src/dev/net/ethertap.cc | 35 ++++++++++++++++++++++++++++------- 1 file changed, 28 insertions(+), 7 deletions(-) diff --git a/src/dev/net/ethertap.cc b/src/dev/net/ethertap.cc index 8d08cc2d2..4e32a8c46 100644 --- a/src/dev/net/ethertap.cc +++ b/src/dev/net/ethertap.cc @@ -406,7 +406,7 @@ EtherTapStub::sendReal(const void *data, size_t len) EtherTap::EtherTap(const Params *p) : EtherTapBase(p) { - int fd = open(p->tun_clone_device.c_str(), O_RDWR); + int fd = open(p->tun_clone_device.c_str(), O_RDWR | O_NONBLOCK); if (fd < 0) panic("Couldn't open %s.\n", p->tun_clone_device); @@ -438,18 +438,39 @@ EtherTap::recvReal(int revent) if (!(revent & POLLIN)) return; - ssize_t ret = read(tap, buffer, buflen); - if (ret < 0) - panic("Failed to read from tap device.\n"); + ssize_t ret; + while ((ret = read(tap, buffer, buflen))) { + if (ret < 0) { + if (errno == EAGAIN) + break; + panic("Failed to read from tap device.\n"); + } - sendSimulated(buffer, ret); + sendSimulated(buffer, ret); + } } bool EtherTap::sendReal(const void *data, size_t len) { - if (write(tap, data, len) != len) - panic("Failed to write data to tap device.\n"); + int n; + pollfd pfd[1]; + pfd->fd = tap; + pfd->events = POLLOUT; + + // `tap` is a nonblock fd. Here we try to write until success, and use + // poll to make a blocking wait. + while ((n = write(tap, data, len)) != len) { + if (errno != EAGAIN) + panic("Failed to write data to tap device.\n"); + pfd->revents = 0; + int ret = poll(pfd, 1, -1); + // timeout is set to inf, we shouldn't get 0 in any case. + assert(ret != 0); + if (ret == -1 || (ret == 1 && (pfd->revents & POLLERR))) { + panic("Failed when polling to write data to tap device.\n"); + } + } return true; } -- 2.30.2