extremecoders-re

Setting up Qemu with a tap interface

There are two parts to networking within QEMU:

• The virtual network device that is provided to the guest (e.g. a PCI network card).
• The network backend that interacts with the emulated NIC (e.g. puts packets onto the host's network).

Example: User mode network

laoar

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/device.h>
#include <linux/init.h> 
#include <linux/fs.h> 
#include <linux/mm.h> 
#include <asm/uaccess.h>

#define MAX_SIZE (PAGE_SIZE * 2)   /* max size mmaped to userspace */
#define DEVICE_NAME "mchar"

turtlemonvh

# Borrowed from: 
# https://github.com/silven/go-example/blob/master/Makefile
# https://vic.demuzere.be/articles/golang-makefile-crosscompile/

BINARY = superdo
VET_REPORT = vet.report
TEST_REPORT = tests.xml
GOARCH = amd64

VERSION?=?

dtoma

// https://banu.com/blog/2/how-to-use-epoll-a-complete-example-in-c/
// http://www.kegel.com/poller/

/** Todo
 * - [ ] Split i/o and logic
 * - [ ] Unit test logic
 * - [ ] Logging
 * - [ ] Continuous integration
 *   - [ ] Linux
 *   - [ ] Windows

CMCDragonkai

Understanding the Memory Layout of Linux Executables

Required tools for playing around with memory:

• hexdump
• objdump
• readelf
• xxd
• gcore

jbenet

// Package main demonstrates a problem with sockets.
// run it with:
//
//   go build
//   ./test 127.0.0.1:1234
//
// Nevermind, found the problem (using select wrong)
//
package main

jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

tonyc

Using strace and lsof to debug blocked processes

You can use strace on a specific pid to figure out what a specific process is doing, e.g.:

strace -fp <pid>

You might see something like:

select(9, [3 5 8], [], [], {0, 999999}) = 0 (Timeout)

glacjay

import fcntl
import os
import struct
import subprocess


# Some constants used to ioctl the device file. I got them by a simple C
# program.
TUNSETIFF = 0x400454ca
TUNSETOWNER = TUNSETIFF + 2