1      __
2 (___()'`;  Rusty's Remarkably Unreliable Guide to Lguest
3 /,    /`      - or, A Young Coder's Illustrated Hypervisor
4 \\"--\\    http://lguest.ozlabs.org
5
6Lguest is designed to be a minimal 32-bit x86 hypervisor for the Linux kernel,
7for Linux developers and users to experiment with virtualization with the
8minimum of complexity.  Nonetheless, it should have sufficient features to
9make it useful for specific tasks, and, of course, you are encouraged to fork
10and enhance it (see drivers/lguest/README).
11
12Features:
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
19Developer 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
25Running 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
122There is a helpful mailing list at http://ozlabs.org/mailman/listinfo/lguest
123
124Good luck!
125Rusty Russell rusty@rustcorp.com.au.
126