The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/tools/lguest/lguest.txt

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    1       __
    2  (___()'`;  Rusty's Remarkably Unreliable Guide to Lguest
    3  /,    /`      - or, A Young Coder's Illustrated Hypervisor
    4  \\"--\\    http://lguest.ozlabs.org
    5 
    6 Lguest is designed to be a minimal 32-bit x86 hypervisor for the Linux kernel,
    7 for Linux developers and users to experiment with virtualization with the
    8 minimum of complexity.  Nonetheless, it should have sufficient features to
    9 make it useful for specific tasks, and, of course, you are encouraged to fork
   10 and enhance it (see drivers/lguest/README).
   11 
   12 Features:
   13 
   14 - Kernel module which runs in a normal kernel.
   15 - Simple I/O model for communication.
   16 - Simple program to create new guests.
   17 - Logo contains cute puppies: http://lguest.ozlabs.org
   18 
   19 Developer features:
   20 
   21 - Fun to hack on.
   22 - No ABI: being tied to a specific kernel anyway, you can change anything.
   23 - Many opportunities for improvement or feature implementation.
   24 
   25 Running Lguest:
   26 
   27 - The easiest way to run lguest is to use same kernel as guest and host.
   28   You can configure them differently, but usually it's easiest not to.
   29 
   30   You will need to configure your kernel with the following options:
   31 
   32   "General setup":
   33      "Prompt for development and/or incomplete code/drivers" = Y
   34         (CONFIG_EXPERIMENTAL=y)
   35 
   36   "Processor type and features":
   37      "Paravirtualized guest support" = Y
   38         "Lguest guest support" = Y
   39      "High Memory Support" = off/4GB
   40      "Alignment value to which kernel should be aligned" = 0x100000
   41         (CONFIG_PARAVIRT=y, CONFIG_LGUEST_GUEST=y, CONFIG_HIGHMEM64G=n and
   42          CONFIG_PHYSICAL_ALIGN=0x100000)
   43 
   44   "Device Drivers":
   45      "Block devices"
   46         "Virtio block driver (EXPERIMENTAL)" = M/Y
   47      "Network device support"
   48         "Universal TUN/TAP device driver support" = M/Y
   49         "Virtio network driver (EXPERIMENTAL)" = M/Y
   50            (CONFIG_VIRTIO_BLK=m, CONFIG_VIRTIO_NET=m and CONFIG_TUN=m)
   51 
   52   "Virtualization"
   53      "Linux hypervisor example code" = M/Y
   54         (CONFIG_LGUEST=m)
   55 
   56 - A tool called "lguest" is available in this directory: type "make"
   57   to build it.  If you didn't build your kernel in-tree, use "make
   58   O=<builddir>".
   59 
   60 - Create or find a root disk image.  There are several useful ones
   61   around, such as the xm-test tiny root image at
   62           http://xm-test.xensource.com/ramdisks/initrd-1.1-i386.img
   63 
   64   For more serious work, I usually use a distribution ISO image and
   65   install it under qemu, then make multiple copies:
   66 
   67           dd if=/dev/zero of=rootfile bs=1M count=2048
   68           qemu -cdrom image.iso -hda rootfile -net user -net nic -boot d
   69 
   70   Make sure that you install a getty on /dev/hvc0 if you want to log in on the
   71   console!
   72 
   73 - "modprobe lg" if you built it as a module.
   74 
   75 - Run an lguest as root:
   76 
   77       Documentation/virtual/lguest/lguest 64 vmlinux --tunnet=192.168.19.1 \
   78         --block=rootfile root=/dev/vda
   79 
   80    Explanation:
   81     64: the amount of memory to use, in MB.
   82 
   83     vmlinux: the kernel image found in the top of your build directory.  You
   84        can also use a standard bzImage.
   85 
   86     --tunnet=192.168.19.1: configures a "tap" device for networking with this
   87        IP address.
   88 
   89     --block=rootfile: a file or block device which becomes /dev/vda
   90        inside the guest.
   91 
   92     root=/dev/vda: this (and anything else on the command line) are
   93        kernel boot parameters.
   94 
   95 - Configuring networking.  I usually have the host masquerade, using
   96   "iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE" and "echo 1 >
   97   /proc/sys/net/ipv4/ip_forward".  In this example, I would configure
   98   eth0 inside the guest at 192.168.19.2.
   99 
  100   Another method is to bridge the tap device to an external interface
  101   using --tunnet=bridge:<bridgename>, and perhaps run dhcp on the guest
  102   to obtain an IP address.  The bridge needs to be configured first:
  103   this option simply adds the tap interface to it.
  104 
  105   A simple example on my system:
  106 
  107     ifconfig eth0 0.0.0.0
  108     brctl addbr lg0
  109     ifconfig lg0 up
  110     brctl addif lg0 eth0
  111     dhclient lg0
  112 
  113   Then use --tunnet=bridge:lg0 when launching the guest.
  114 
  115   See:
  116   
  117     http://www.linuxfoundation.org/collaborate/workgroups/networking/bridge
  118     
  119   for general information on how to get bridging to work.
  120 
  121 - Random number generation. Using the --rng option will provide a
  122   /dev/hwrng in the guest that will read from the host's /dev/random.
  123   Use this option in conjunction with rng-tools (see ../hw_random.txt)
  124   to provide entropy to the guest kernel's /dev/random.
  125 
  126 There is a helpful mailing list at http://ozlabs.org/mailman/listinfo/lguest
  127 
  128 Good luck!
  129 Rusty Russell rusty@rustcorp.com.au.

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