tools/lguest/lguest.txt

   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   "Processor type and features":
  33      "Paravirtualized guest support" = Y
  34         "Lguest guest support" = Y
  35      "High Memory Support" = off/4GB
  36      "Alignment value to which kernel should be aligned" = 0x100000
  37         (CONFIG_PARAVIRT=y, CONFIG_LGUEST_GUEST=y, CONFIG_HIGHMEM64G=n and
  38          CONFIG_PHYSICAL_ALIGN=0x100000)
  39
  40   "Device Drivers":
  41      "Block devices"
  42         "Virtio block driver" = M/Y
  43      "Network device support"
  44         "Universal TUN/TAP device driver support" = M/Y
  45         "Virtio network driver" = M/Y
  46            (CONFIG_VIRTIO_BLK=m, CONFIG_VIRTIO_NET=m and CONFIG_TUN=m)
  47
  48   "Virtualization"
  49      "Linux hypervisor example code" = M/Y
  50         (CONFIG_LGUEST=m)
  51
  52 - A tool called "lguest" is available in this directory: type "make"
  53   to build it.  If you didn't build your kernel in-tree, use "make
  54   O=<builddir>".
  55
  56 - Create or find a root disk image.  There are several useful ones
  57   around, such as the xm-test tiny root image at
  58           http://xm-test.xensource.com/ramdisks/initrd-1.1-i386.img
  59
  60   For more serious work, I usually use a distribution ISO image and
  61   install it under qemu, then make multiple copies:
  62
  63           dd if=/dev/zero of=rootfile bs=1M count=2048
  64           qemu -cdrom image.iso -hda rootfile -net user -net nic -boot d
  65
  66   Make sure that you install a getty on /dev/hvc0 if you want to log in on the
  67   console!
  68
  69 - "modprobe lg" if you built it as a module.
  70
  71 - Run an lguest as root:
  72
  73       tools/lguest/lguest 64 vmlinux --tunnet=192.168.19.1 \
  74         --block=rootfile root=/dev/vda
  75
  76    Explanation:
  77     64: the amount of memory to use, in MB.
  78
  79     vmlinux: the kernel image found in the top of your build directory.  You
  80        can also use a standard bzImage.
  81
  82     --tunnet=192.168.19.1: configures a "tap" device for networking with this
  83        IP address.
  84
  85     --block=rootfile: a file or block device which becomes /dev/vda
  86        inside the guest.
  87
  88     root=/dev/vda: this (and anything else on the command line) are
  89        kernel boot parameters.
  90
  91 - Configuring networking.  I usually have the host masquerade, using
  92   "iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE" and "echo 1 >
  93   /proc/sys/net/ipv4/ip_forward".  In this example, I would configure
  94   eth0 inside the guest at 192.168.19.2.
  95
  96   Another method is to bridge the tap device to an external interface
  97   using --tunnet=bridge:<bridgename>, and perhaps run dhcp on the guest
  98   to obtain an IP address.  The bridge needs to be configured first:
  99   this option simply adds the tap interface to it.
 100
 101   A simple example on my system:
 102
 103     ifconfig eth0 0.0.0.0
 104     brctl addbr lg0
 105     ifconfig lg0 up
 106     brctl addif lg0 eth0
 107     dhclient lg0
 108
 109   Then use --tunnet=bridge:lg0 when launching the guest.
 110
 111   See:
 112
 113     http://www.linuxfoundation.org/collaborate/workgroups/networking/bridge
 114
 115   for general information on how to get bridging to work.
 116
 117 - Random number generation. Using the --rng option will provide a
 118   /dev/hwrng in the guest that will read from the host's /dev/random.
 119   Use this option in conjunction with rng-tools (see ../hw_random.txt)
 120   to provide entropy to the guest kernel's /dev/random.
 121
 122 There is a helpful mailing list at http://ozlabs.org/mailman/listinfo/lguest
 123
 124 Good luck!
 125 Rusty Russell rusty@rustcorp.com.au.