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  "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/lguest/lguest 64 vmlinux --tunnet=192.168.19.1 --block=rootfile root=/dev/vda
78
79   Explanation:
80    64: the amount of memory to use, in MB.
81
82    vmlinux: the kernel image found in the top of your build directory.  You
83       can also use a standard bzImage.
84
85    --tunnet=192.168.19.1: configures a "tap" device for networking with this
86       IP address.
87
88    --block=rootfile: a file or block device which becomes /dev/vda
89       inside the guest.
90
91    root=/dev/vda: this (and anything else on the command line) are
92       kernel boot parameters.
93
94- Configuring networking.  I usually have the host masquerade, using
95  "iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE" and "echo 1 >
96  /proc/sys/net/ipv4/ip_forward".  In this example, I would configure
97  eth0 inside the guest at 192.168.19.2.
98
99  Another method is to bridge the tap device to an external interface
100  using --tunnet=bridge:<bridgename>, and perhaps run dhcp on the guest
101  to obtain an IP address.  The bridge needs to be configured first:
102  this option simply adds the tap interface to it.
103
104  A simple example on my system:
105
106    ifconfig eth0 0.0.0.0
107    brctl addbr lg0
108    ifconfig lg0 up
109    brctl addif lg0 eth0
110    dhclient lg0
111
112  Then use --tunnet=bridge:lg0 when launching the guest.
113
114  See:
115
116    http://www.linuxfoundation.org/collaborate/workgroups/networking/bridge
117
118  for general information on how to get bridging to work.
119
120- Random number generation. Using the --rng option will provide a
121  /dev/hwrng in the guest that will read from the host's /dev/random.
122  Use this option in conjunction with rng-tools (see ../hw_random.txt)
123  to provide entropy to the guest kernel's /dev/random.
124
125There is a helpful mailing list at http://ozlabs.org/mailman/listinfo/lguest
126
127Good luck!
128Rusty Russell rusty@rustcorp.com.au.
129