__
   (___()'`;  Rusty's Remarkably Unreliable Guide to Lguest
   /,    /`      - or, A Young Coder's Illustrated Hypervisor
   \\"--\\    http://lguest.ozlabs.org

  Lguest is designed to be a minimal 32-bit x86 hypervisor for the Linux kernel,
  for Linux developers and users to experiment with virtualization with the
  minimum of complexity.  Nonetheless, it should have sufficient features to
  make it useful for specific tasks, and, of course, you are encouraged to fork
  and enhance it (see drivers/lguest/README).

  
  Features:
  
  - Kernel module which runs in a normal kernel.
  - Simple I/O model for communication.
  - Simple program to create new guests.
  - Logo contains cute puppies: http://lguest.ozlabs.org
  
  Developer features:
  
  - Fun to hack on.
  - No ABI: being tied to a specific kernel anyway, you can change anything.
  - Many opportunities for improvement or feature implementation.
  
  Running Lguest:

  - The easiest way to run lguest is to use same kernel as guest and host.
    You can configure them differently, but usually it's easiest not to.

  
    You will need to configure your kernel with the following options:

    "General setup":
       "Prompt for development and/or incomplete code/drivers" = Y
          (CONFIG_EXPERIMENTAL=y)
  
    "Processor type and features":
       "Paravirtualized guest support" = Y
          "Lguest guest support" = Y
       "High Memory Support" = off/4GB
       "Alignment value to which kernel should be aligned" = 0x100000
          (CONFIG_PARAVIRT=y, CONFIG_LGUEST_GUEST=y, CONFIG_HIGHMEM64G=n and
           CONFIG_PHYSICAL_ALIGN=0x100000)
  
    "Device Drivers":

       "Block devices"
          "Virtio block driver (EXPERIMENTAL)" = M/Y

       "Network device support"
          "Universal TUN/TAP device driver support" = M/Y

          "Virtio network driver (EXPERIMENTAL)" = M/Y
             (CONFIG_VIRTIO_BLK=m, CONFIG_VIRTIO_NET=m and CONFIG_TUN=m)
  
    "Virtualization"
       "Linux hypervisor example code" = M/Y
          (CONFIG_LGUEST=m)

  
  - A tool called "lguest" is available in this directory: type "make"
    to build it.  If you didn't build your kernel in-tree, use "make
    O=<builddir>".
  
  - Create or find a root disk image.  There are several useful ones
    around, such as the xm-test tiny root image at
  	  http://xm-test.xensource.com/ramdisks/initrd-1.1-i386.img
  
    For more serious work, I usually use a distribution ISO image and
    install it under qemu, then make multiple copies:
  
  	  dd if=/dev/zero of=rootfile bs=1M count=2048
  	  qemu -cdrom image.iso -hda rootfile -net user -net nic -boot d

    Make sure that you install a getty on /dev/hvc0 if you want to log in on the
    console!

  - "modprobe lg" if you built it as a module.
  
  - Run an lguest as root:

        Documentation/virtual/lguest/lguest 64 vmlinux --tunnet=192.168.19.1 \
          --block=rootfile root=/dev/vda

  
     Explanation:

      64: the amount of memory to use, in MB.

  
      vmlinux: the kernel image found in the top of your build directory.  You
         can also use a standard bzImage.
  
      --tunnet=192.168.19.1: configures a "tap" device for networking with this
         IP address.

      --block=rootfile: a file or block device which becomes /dev/vda

         inside the guest.

      root=/dev/vda: this (and anything else on the command line) are

         kernel boot parameters.
  
  - Configuring networking.  I usually have the host masquerade, using
    "iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE" and "echo 1 >
    /proc/sys/net/ipv4/ip_forward".  In this example, I would configure
    eth0 inside the guest at 192.168.19.2.
  
    Another method is to bridge the tap device to an external interface
    using --tunnet=bridge:<bridgename>, and perhaps run dhcp on the guest
    to obtain an IP address.  The bridge needs to be configured first:
    this option simply adds the tap interface to it.
  
    A simple example on my system:
  
      ifconfig eth0 0.0.0.0
      brctl addbr lg0
      ifconfig lg0 up
      brctl addif lg0 eth0
      dhclient lg0
  
    Then use --tunnet=bridge:lg0 when launching the guest.

    See:
    
      http://www.linuxfoundation.org/collaborate/workgroups/networking/bridge
      
    for general information on how to get bridging to work.

  - Random number generation. Using the --rng option will provide a
    /dev/hwrng in the guest that will read from the host's /dev/random.
    Use this option in conjunction with rng-tools (see ../hw_random.txt)
    to provide entropy to the guest kernel's /dev/random.

  There is a helpful mailing list at http://ozlabs.org/mailman/listinfo/lguest

  Good luck!

  Rusty Russell rusty@rustcorp.com.au.