qemu的使用

一、QEMU的运行模式

直接摘抄自己《揭秘家用路由器0day漏洞挖掘技术》，网上查了一下也没有找到令人满意的QEMU的使用说明，就采用这本书上的介绍。如果后期能够找到比较满意的QEMU的使用方法的说明，再添加上来。

QEMU模拟器主要有两种比较常见的运作模式：User Mode（使用者模式）、System Mode（系统模式）。User Mode模式下，用户只需要将各种不同平台的处理编译得到的Linux程序放在QEMU虚拟中运行即可，其他的事情全部由QEMU虚拟机来完成，不需要用户自定义内核和虚拟磁盘等文件；System Mode模式下，最明显的特点是用户可以为QEMU虚拟机指定运行的内核或者虚拟硬盘等文件，简单来说系统模式下QEMU虚拟机是可根据用户的要求配置的。

二、QEMU在使用者模式下执行程序

当程序是静态编译（gcc编译的时候，加了静态编译选项 "-static" ）完成，运行时 不需要依赖动态链接库 ，在使用QEMU运行编译好的Linux程序使用下面的命令就好：

# 查看可执行程序hello的文件类型MIPS32
$ file hello
hello: ELF 32-bit MSB executable, MIPS, MIPS32 version 1 (SYSV), statically linked, not stripped  

$ cp $(which qemu-mips) ./  

# 使用qemu-mips加载hello程序
$ ./qemu-mips hello "Hello World"
Hello World

执行结果截图：

当程序是动态编译（gcc编译的时候，没有静态编译选项 "-static" ）完成，程序运行时 需要依赖动态链接库 ，在使用QEMU运行编译好的Linux程序使用下面的命令就好：

# 查看即将执行的文件的类型
$ file bin/busybox  

# 拷贝qemu-mips到当前目录
$ cp $(which qemu-mips) ./  

# 直接运行报错
$ ./qemu-mips bin/busybox  

# 更改QEMU-MIPS执行的根目录到当前目录
$ sudo chroot . ./qemu-mips ./bin/busybox  

执行的结果截图：

QEMU使用者模式下使用的命令行帮助，以 qemu-mipsel 为例：

fly2016@ubuntu:~$ qemu-mipsel --help
usage: qemu-mipsel [options] program [arguments...]
Linux CPU emulator (compiled for mipsel emulation)  

Options and associated environment variables:  

Argument      Env-variable      Description
-h                              print this help
-help
-g port       QEMU_GDB          wait gdb connection to 'port'
-L path       QEMU_LD_PREFIX    set the elf interpreter prefix to 'path'
-s size       QEMU_STACK_SIZE   set the stack size to 'size' bytes
-cpu model    QEMU_CPU          select CPU (-cpu help for list)
-E var=value  QEMU_SET_ENV      sets targets environment variable (see below)
-U var        QEMU_UNSET_ENV    unsets targets environment variable (see below)
-0 argv0      QEMU_ARGV0        forces target process argv[0] to be 'argv0'
-r uname      QEMU_UNAME        set qemu uname release string to 'uname'
-B address    QEMU_GUEST_BASE   set guest_base address to 'address'
-R size       QEMU_RESERVED_VA  reserve 'size' bytes for guest virtual address space
-d item[,...] QEMU_LOG          enable logging of specified items (use '-d help' for a list of items)
-D logfile    QEMU_LOG_FILENAME write logs to 'logfile' (default stderr)
-p pagesize   QEMU_PAGESIZE     set the host page size to 'pagesize'
-singlestep   QEMU_SINGLESTEP   run in singlestep mode
-strace       QEMU_STRACE       log system calls
-seed         QEMU_RAND_SEED    Seed for pseudo-random number generator
-trace        QEMU_TRACE        [[enable=]<pattern>][,events=<file>][,file=<file>]
-version      QEMU_VERSION      display version information and exit  

Defaults:
QEMU_LD_PREFIX  = /usr/gnemul/qemu-mipsel
QEMU_STACK_SIZE = 8388608 byte  

You can use -E and -U options or the QEMU_SET_ENV and
QEMU_UNSET_ENV environment variables to set and unset
environment variables for the target process.
It is possible to provide several variables by separating them
by commas in getsubopt(3) style. Additionally it is possible to
provide the -E and -U options multiple times.
The following lines are equivalent:
    -E var1=val2 -E var2=val2 -U LD_PRELOAD -U LD_DEBUG
    -E var1=val2,var2=val2 -U LD_PRELOAD,LD_DEBUG
    QEMU_SET_ENV=var1=val2,var2=val2 QEMU_UNSET_ENV=LD_PRELOAD,LD_DEBUG
Note that if you provide several changes to a single variable
the last change will stay in effect.

三、QEMU的系统模式使用

QEMU运行在系统模式下，需要为QEMU指定 内核镜像、IDE硬盘0/1镜像、内核命令行 等参数，QEMU虚拟机才能正常运行。Debian官网提供了QEMU虚拟机各种平台架构的内核镜像、硬盘文件镜像文件的下载，下载地址为：https://people.debian.org/~aurel32/qemu/，其中mips为大端机的，mipsel为小端机的。

这里以下载 mips大端机 的虚拟机镜像文件为例，具体的下载网址为：

https://people.debian.org/~aurel32/qemu/mips/

，点击进去以后会发现mips虚拟机镜像文件的下载说明。我们根据mips虚拟机镜像文件的使用命令参数进行选择性的下载。

Debian Squeeze and Wheezy mips images for QEMU
==============================================  

This directory contains Debian Squeeze and Wheezy mips images for QEMU and
the corresponding kernels and initrds:
  1d58f831f5e5064753c0c138d8d74057  debian_squeeze_mips_standard.qcow2
  cb56139b63b88fdb38776051d28bb750  vmlinux-2.6.32-5-4kc-malta
  7165e80b0e5c5c3e40f2ca46401373ce  vmlinux-2.6.32-5-5kc-malta
  bf699f435160b0bd9ac62905fa64701e  debian_wheezy_mips_standard.qcow2
  1fecbe19ff49a6fd715901483b23647c  vmlinux-3.2.0-4-4kc-malta
  19e6e853d4a7a7b9ed5e787b7f875835  vmlinux-3.2.0-4-5kc-malta  

Both images are 25GiB images in QCOW2 format on which a Debian Squeeze or
Wheezy "Standard system" installation has been performed. The other
installation options are the following:
  - Keyboard:       US
  - Locale:         en_US
  - Mirror:         ftp.debian.org
  - Hostname:       debian-mips
  - Root password:  root
  - User account:   user
  - User password:  user  

To use this image, you need to install QEMU 1.1.0 (or later). Start QEMU
with the following arguments for a 32-bit machine:
  - qemu-system-mips -M malta -kernel vmlinux-2.6.32-5-4kc-malta -hda debian_squeeze_mips_standard.qcow2 -append "root=/dev/sda1 console=tty0"
  - qemu-system-mips -M malta -kernel vmlinux-3.2.0-4-4kc-malta -hda debian_wheezy_mips_standard.qcow2 -append "root=/dev/sda1 console=tty0"  

Start QEMU with the following arguments for a 64-bit machine:
  - qemu-system-mips64 -M malta -kernel vmlinux-2.6.32-5-5kc-malta -hda debian_squeeze_mips_standard.qcow2 -append "root=/dev/sda1 console=tty0"
  - qemu-system-mips64 -M malta -kernel vmlinux-3.2.0-4-5kc-malta -hda debian_wheezy_mips_standard.qcow2 -append "root=/dev/sda1 console=tty0"  

By default QEMU emulates a machine with 128MiB of RAM. You can use the -m option
to increase or decrease the size of the RAM. It is however limited to 256MiB
with a 32-bit kernel. With a 64-bit kernel and QEMU >= 1.7, it is possible to
use up to 2047MiB of RAM, passing the memory map to the kernel, adding a mem=
argument to the append parameters as follow: "mem=256m@0x0 mem=XXXm@0x90000000"
where XXX represents the total memory size minus 256MiB. If you don't want to
start QEMU in graphic mode, you can use the -nographic option. The image is
configured to display a login prompt on the first serial port (ttys0). If you
want to switch the boot messages to the serial port, you need to replace
"console=tty0" by "console=ttyS0".

这里下载内核文件 vmlinux-2.6.32-5-4kc-malta，磁盘镜像 debian_squeeze_mips_standard.qcow2 作为mips虚拟机的配置文件。

ubuntu下可以使用下面的命令进行mips和mipsel虚拟机镜像配置文件的下载：

# +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# Start QEMU with the following arguments for a 32-bit machine:
$ qemu-system-mips -M malta -kernel vmlinux-2.6.32-5-4kc-malta -hda debian_squeeze_mips_standard.qcow2 -append "root=/dev/sda1 console=tty0"
$ qemu-system-mips -M malta -kernel vmlinux-3.2.0-4-4kc-malta -hda debian_wheezy_mips_standard.qcow2 -append "root=/dev/sda1 console=tty0"  

# for MIPS 32bit ###############:
# 内核版本为2.6.x
$ wget https://people.debian.org/~aurel32/qemu/mips/vmlinux-2.6.32-5-4kc-malta
$ wget https://people.debian.org/~aurel32/qemu/mips/debian_squeeze_mips_standard.qcow2  

# 内核版本为3.2.x
$ wget https://people.debian.org/~aurel32/qemu/mips/vmlinux-3.2.0-4-4kc-malta
$ wget https://people.debian.org/~aurel32/qemu/mips/debian_wheezy_mips_standard.qcow2  

# +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# Start QEMU with the following arguments for a 64-bit machine:
$ qemu-system-mips64 -M malta -kernel vmlinux-2.6.32-5-5kc-malta -hda debian_squeeze_mips_standard.qcow2 -append "root=/dev/sda1 console=tty0"
$ qemu-system-mips64 -M malta -kernel vmlinux-3.2.0-4-5kc-malta -hda debian_wheezy_mips_standard.qcow2 -append "root=/dev/sda1 console=tty0"  

# for MIPS 64bit ###############:
# 内核版本为2.6.x
$ wget https://people.debian.org/~aurel32/qemu/mips/vmlinux-2.6.32-5-5kc-malta
$ wget https://people.debian.org/~aurel32/qemu/mips/debian_squeeze_mips_standard.qcow2  

# 内核版本为3.2.x
$ wget https://people.debian.org/~aurel32/qemu/mips/vmlinux-3.2.0-4-5kc-malta
$ wget https://people.debian.org/~aurel32/qemu/mips/debian_wheezy_mips_standard.qcow2  

# +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# Start QEMU with the following arguments for a 32-bit machine:
$ qemu-system-mipsel -M malta -kernel vmlinux-2.6.32-5-4kc-malta -hda debian_squeeze_mipsel_standard.qcow2 -append "root=/dev/sda1 console=tty0"
$ qemu-system-mipsel -M malta -kernel vmlinux-3.2.0-4-4kc-malta -hda debian_wheezy_mipsel_standard.qcow2 -append "root=/dev/sda1 console=tty0"  

# for MIPSEL 32bit ###############:
# 内核版本为2.6.x
$ wget https://people.debian.org/~aurel32/qemu/mipsel/vmlinux-2.6.32-5-4kc-malta
$ wget https://people.debian.org/~aurel32/qemu/mipsel/debian_squeeze_mipsel_standard.qcow2  

# 内核版本为3.2.x
$ wget https://people.debian.org/~aurel32/qemu/mipsel/vmlinux-3.2.0-4-4kc-malta
$ wget https://people.debian.org/~aurel32/qemu/mipsel/debian_wheezy_mipsel_standard.qcow2  

# +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# Start QEMU with the following arguments for a 64-bit machine:
$ qemu-system-mips64el -M malta -kernel vmlinux-2.6.32-5-5kc-malta -hda debian_squeeze_mipsel_standard.qcow2 -append "root=/dev/sda1 console=tty0"
$ qemu-system-mips64el -M malta -kernel vmlinux-3.2.0-4-5kc-malta -hda debian_wheezy_mipsel_standard.qcow2 -append "root=/dev/sda1 console=tty0"  

# for MIPSEL 64bit ###############:
# 内核版本为2.6.x
$ wget https://people.debian.org/~aurel32/qemu/mipsel/vmlinux-2.6.32-5-5kc-malta
$ wget https://people.debian.org/~aurel32/qemu/mipsel/debian_squeeze_mipsel_standard.qcow2  

# 内核版本为3.2.x
$ wget https://people.debian.org/~aurel32/qemu/mipsel/vmlinux-3.2.0-4-5kc-malta
$ wget https://people.debian.org/~aurel32/qemu/mipsel/debian_wheezy_mipsel_standard.qcow2

使用 qemu-system-mips 启动内核2.6.x版本MIPS 32bit的QEMU虚拟机镜像，QEMU启动失败，结果如下图：

$ sudo qemu-system-mips -M malta -kernel vmlinux-2.6.32-5-4kc-malta -hda debian_squeeze_mips_standard.qcow2 -append "root=/dev/sda1 console=tty0" -nographic

以控制台的形式启动QEMU虚拟机成功，结果如图：

QEMU系统者模式下使用的命令行帮助，以 qemu-system-mips 为例，功能挺强大的：

fly2016@ubuntu:~$ qemu-system-mips -h
QEMU emulator version 2.8.92 (v2.9.0-rc2-42-g6499fd1-dirty)
Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers
usage: qemu-system-mips [options] [disk_image]  

'disk_image' is a raw hard disk image for IDE hard disk 0  

Standard options:
-h or -help     display this help and exit
-version        display version information and exit
-machine [type=]name[,prop[=value][,...]]
                selects emulated machine ('-machine help' for list)
                property accel=accel1[:accel2[:...]] selects accelerator
                supported accelerators are kvm, xen, tcg (default: tcg)
                kernel_irqchip=on|off|split controls accelerated irqchip support (default=off)
                vmport=on|off|auto controls emulation of vmport (default: auto)
                kvm_shadow_mem=size of KVM shadow MMU in bytes
                dump-guest-core=on|off include guest memory in a core dump (default=on)
                mem-merge=on|off controls memory merge support (default: on)
                igd-passthru=on|off controls IGD GFX passthrough support (default=off)
                aes-key-wrap=on|off controls support for AES key wrapping (default=on)
                dea-key-wrap=on|off controls support for DEA key wrapping (default=on)
                suppress-vmdesc=on|off disables self-describing migration (default=off)
                nvdimm=on|off controls NVDIMM support (default=off)
                enforce-config-section=on|off enforce configuration section migration (default=off)
-cpu cpu        select CPU ('-cpu help' for list)
-accel [accel=]accelerator[,thread=single|multi]
               select accelerator ('-accel help for list')
               thread=single|multi (enable multi-threaded TCG)-smp [cpus=]n[,maxcpus=cpus][,cores=cores][,threads=threads][,sockets=sockets]
                set the number of CPUs to 'n' [default=1]
                maxcpus= maximum number of total cpus, including
                offline CPUs for hotplug, etc
                cores= number of CPU cores on one socket
                threads= number of threads on one CPU core
                sockets= number of discrete sockets in the system
-numa node[,mem=size][,cpus=firstcpu[-lastcpu]][,nodeid=node]
-numa node[,memdev=id][,cpus=firstcpu[-lastcpu]][,nodeid=node]
-add-fd fd=fd,set=set[,opaque=opaque]
                Add 'fd' to fd 'set'
-set group.id.arg=value
                set <arg> parameter for item <id> of type <group>
                i.e. -set drive.$id.file=/path/to/image
-global driver.property=value
-global driver=driver,property=property,value=value
                set a global default for a driver property
-boot [order=drives][,once=drives][,menu=on|off]
      [,splash=sp_name][,splash-time=sp_time][,reboot-timeout=rb_time][,strict=on|off]
                'drives': floppy (a), hard disk (c), CD-ROM (d), network (n)
                'sp_name': the file's name that would be passed to bios as logo picture, if menu=on
                'sp_time': the period that splash picture last if menu=on, unit is ms
                'rb_timeout': the timeout before guest reboot when boot failed, unit is ms
-m [size=]megs[,slots=n,maxmem=size]
                configure guest RAM
                size: initial amount of guest memory
                slots: number of hotplug slots (default: none)
                maxmem: maximum amount of guest memory (default: none)
NOTE: Some architectures might enforce a specific granularity
-mem-path FILE  provide backing storage for guest RAM
-mem-prealloc   preallocate guest memory (use with -mem-path)
-k language     use keyboard layout (for example 'fr' for French)
-audio-help     print list of audio drivers and their options
-soundhw c1,... enable audio support
                and only specified sound cards (comma separated list)
                use '-soundhw help' to get the list of supported cards
                use '-soundhw all' to enable all of them
-balloon none   disable balloon device
-balloon virtio[,addr=str]
                enable virtio balloon device (default)
-device driver[,prop[=value][,...]]
                add device (based on driver)
                prop=value,... sets driver properties
                use '-device help' to print all possible drivers
                use '-device driver,help' to print all possible properties
-name string1[,process=string2][,debug-threads=on|off]
                set the name of the guest
                string1 sets the window title and string2 the process name (on Linux)
                When debug-threads is enabled, individual threads are given a separate name (on Linux)
                NOTE: The thread names are for debugging and not a stable API.
-uuid %08x-%04x-%04x-%04x-%012x
                specify machine UUID
:
Block device options:
-fda/-fdb file  use 'file' as floppy disk 0/1 image
-hda/-hdb file  use 'file' as IDE hard disk 0/1 image
-hdc/-hdd file  use 'file' as IDE hard disk 2/3 image
-cdrom file     use 'file' as IDE cdrom image (cdrom is ide1 master)
-blockdev [driver=]driver[,node-name=N][,discard=ignore|unmap]
          [,cache.direct=on|off][,cache.no-flush=on|off]
          [,read-only=on|off][,detect-zeroes=on|off|unmap]
          [,driver specific parameters...]
                configure a block backend
-drive [file=file][,if=type][,bus=n][,unit=m][,media=d][,index=i]
       [,cyls=c,heads=h,secs=s[,trans=t]][,snapshot=on|off]
       [,cache=writethrough|writeback|none|directsync|unsafe][,format=f]
       [,serial=s][,addr=A][,rerror=ignore|stop|report]
       [,werror=ignore|stop|report|enospc][,id=name][,aio=threads|native]
       [,readonly=on|off][,copy-on-read=on|off]
       [,discard=ignore|unmap][,detect-zeroes=on|off|unmap]
       [[,bps=b]|[[,bps_rd=r][,bps_wr=w]]]
       [[,iops=i]|[[,iops_rd=r][,iops_wr=w]]]
       [[,bps_max=bm]|[[,bps_rd_max=rm][,bps_wr_max=wm]]]
       [[,iops_max=im]|[[,iops_rd_max=irm][,iops_wr_max=iwm]]]
       [[,iops_size=is]]
       [[,group=g]]
                use 'file' as a drive image
-mtdblock file  use 'file' as on-board Flash memory image
-sd file        use 'file' as SecureDigital card image
-pflash file    use 'file' as a parallel flash image
-snapshot       write to temporary files instead of disk image files
-hdachs c,h,s[,t]
                force hard disk 0 physical geometry and the optional BIOS
                translation (t=none or lba) (usually QEMU can guess them)
-fsdev fsdriver,id=id[,path=path,][security_model={mapped-xattr|mapped-file|passthrough|none}]
 [,writeout=immediate][,readonly][,socket=socket|sock_fd=sock_fd]
 [[,throttling.bps-total=b]|[[,throttling.bps-read=r][,throttling.bps-write=w]]]
 [[,throttling.iops-total=i]|[[,throttling.iops-read=r][,throttling.iops-write=w]]]
 [[,throttling.bps-total-max=bm]|[[,throttling.bps-read-max=rm][,throttling.bps-write-max=wm]]]
 [[,throttling.iops-total-max=im]|[[,throttling.iops-read-max=irm][,throttling.iops-write-max=iwm]]]
 [[,throttling.iops-size=is]]
-virtfs local,path=path,mount_tag=tag,security_model=[mapped-xattr|mapped-file|passthrough|none]
        [,writeout=immediate][,readonly][,socket=socket|sock_fd=sock_fd]
-virtfs_synth Create synthetic file system image
:
USB options:
-usb            enable the USB driver (will be the default soon)
-usbdevice name add the host or guest USB device 'name'
:
Display options:
-display sdl[,frame=on|off][,alt_grab=on|off][,ctrl_grab=on|off]
            [,window_close=on|off][,gl=on|off]
-display gtk[,grab_on_hover=on|off][,gl=on|off]|
-display vnc=<display>[,<optargs>]
-display curses
-display none                select display type
The default display is equivalent to
    "-vnc localhost:0,to=99,id=default"
-nographic      disable graphical output and redirect serial I/Os to console
-curses         shorthand for -display curses
-no-frame       open SDL window without a frame and window decorations
-alt-grab       use Ctrl-Alt-Shift to grab mouse (instead of Ctrl-Alt)
-ctrl-grab      use Right-Ctrl to grab mouse (instead of Ctrl-Alt)
-no-quit        disable SDL window close capability
-sdl            shorthand for -display sdl
-spice [port=port][,tls-port=secured-port][,x509-dir=<dir>]
       [,x509-key-file=<file>][,x509-key-password=<file>]
       [,x509-cert-file=<file>][,x509-cacert-file=<file>]
       [,x509-dh-key-file=<file>][,addr=addr][,ipv4|ipv6|unix]
       [,tls-ciphers=<list>]
       [,tls-channel=[main|display|cursor|inputs|record|playback]]
       [,plaintext-channel=[main|display|cursor|inputs|record|playback]]
       [,sasl][,password=<secret>][,disable-ticketing]
       [,image-compression=[auto_glz|auto_lz|quic|glz|lz|off]]
       [,jpeg-wan-compression=[auto|never|always]]
       [,zlib-glz-wan-compression=[auto|never|always]]
       [,streaming-video=[off|all|filter]][,disable-copy-paste]
       [,disable-agent-file-xfer][,agent-mouse=[on|off]]
       [,playback-compression=[on|off]][,seamless-migration=[on|off]]
       [,gl=[on|off]][,rendernode=<file>]
   enable spice
   at least one of {port, tls-port} is mandatory
-portrait       rotate graphical output 90 deg left (only PXA LCD)
-rotate <deg>   rotate graphical output some deg left (only PXA LCD)
-vga [std|cirrus|vmware|qxl|xenfb|tcx|cg3|virtio|none]
                select video card type
-full-screen    start in full screen
-vnc <display>  shorthand for -display vnc=<display>
:
Network options:
-netdev user,id=str[,ipv4[=on|off]][,net=addr[/mask]][,host=addr]
         [,ipv6[=on|off]][,ipv6-net=addr[/int]][,ipv6-host=addr]
         [,restrict=on|off][,hostname=host][,dhcpstart=addr]
         [,dns=addr][,ipv6-dns=addr][,dnssearch=domain][,tftp=dir]
         [,bootfile=f][,hostfwd=rule][,guestfwd=rule][,smb=dir[,smbserver=addr]]
                configure a user mode network backend with ID 'str',
                its DHCP server and optional services
-netdev tap,id=str[,fd=h][,fds=x:y:...:z][,ifname=name][,script=file][,downscript=dfile]
         [,br=bridge][,helper=helper][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off]
         [,vhostfd=h][,vhostfds=x:y:...:z][,vhostforce=on|off][,queues=n]
         [,poll-us=n]
                configure a host TAP network backend with ID 'str'
                connected to a bridge (default=br0)
                use network scripts 'file' (default=/etc/qemu-ifup)
                to configure it and 'dfile' (default=/etc/qemu-ifdown)
                to deconfigure it
                use '[down]script=no' to disable script execution
                use network helper 'helper' (default=/usr/local/libexec/qemu-bridge-helper) to
                configure it
                use 'fd=h' to connect to an already opened TAP interface
                use 'fds=x:y:...:z' to connect to already opened multiqueue capable TAP interfaces
                use 'sndbuf=nbytes' to limit the size of the send buffer (the
                default is disabled 'sndbuf=0' to enable flow control set 'sndbuf=1048576')
                use vnet_hdr=off to avoid enabling the IFF_VNET_HDR tap flag
                use vnet_hdr=on to make the lack of IFF_VNET_HDR support an error condition
                use vhost=on to enable experimental in kernel accelerator
                    (only has effect for virtio guests which use MSIX)
                use vhostforce=on to force vhost on for non-MSIX virtio guests
                use 'vhostfd=h' to connect to an already opened vhost net device
                use 'vhostfds=x:y:...:z to connect to multiple already opened vhost net devices
                use 'queues=n' to specify the number of queues to be created for multiqueue TAP
                use 'poll-us=n' to speciy the maximum number of microseconds that could be
                spent on busy polling for vhost net
-netdev bridge,id=str[,br=bridge][,helper=helper]
                configure a host TAP network backend with ID 'str' that is
                connected to a bridge (default=br0)
                using the program 'helper (default=/usr/local/libexec/qemu-bridge-helper)
-netdev l2tpv3,id=str,src=srcaddr,dst=dstaddr[,srcport=srcport][,dstport=dstport]
         [,rxsession=rxsession],txsession=txsession[,ipv6=on/off][,udp=on/off]
         [,cookie64=on/off][,counter][,pincounter][,txcookie=txcookie]
         [,rxcookie=rxcookie][,offset=offset]
                configure a network backend with ID 'str' connected to
                an Ethernet over L2TPv3 pseudowire.
                Linux kernel 3.3+ as well as most routers can talk
                L2TPv3. This transport allows connecting a VM to a VM,
                VM to a router and even VM to Host. It is a nearly-universal
                standard (RFC3391). Note - this implementation uses static
                pre-configured tunnels (same as the Linux kernel).
                use 'src=' to specify source address
                use 'dst=' to specify destination address
                use 'udp=on' to specify udp encapsulation
                use 'srcport=' to specify source udp port
                use 'dstport=' to specify destination udp port
                use 'ipv6=on' to force v6
                L2TPv3 uses cookies to prevent misconfiguration as
                well as a weak security measure
                use 'rxcookie=0x012345678' to specify a rxcookie
                use 'txcookie=0x012345678' to specify a txcookie