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Rusty Russell8ca47e02007-07-19 01:49:29 -07001Rusty's Remarkably Unreliable Guide to Lguest
2 - or, A Young Coder's Illustrated Hypervisor
3http://lguest.ozlabs.org
4
5Lguest is designed to be a minimal hypervisor for the Linux kernel, for
6Linux developers and users to experiment with virtualization with the
7minimum of complexity. Nonetheless, it should have sufficient
8features to make it useful for specific tasks, and, of course, you are
Rusty Russell9653c4a2007-10-22 10:56:23 +10009encouraged to fork and enhance it (see drivers/lguest/README).
Rusty Russell8ca47e02007-07-19 01:49:29 -070010
11Features:
12
13- Kernel module which runs in a normal kernel.
14- Simple I/O model for communication.
15- Simple program to create new guests.
16- Logo contains cute puppies: http://lguest.ozlabs.org
17
18Developer features:
19
20- Fun to hack on.
21- No ABI: being tied to a specific kernel anyway, you can change anything.
22- Many opportunities for improvement or feature implementation.
23
24Running Lguest:
25
Rusty Russell9653c4a2007-10-22 10:56:23 +100026- The easiest way to run lguest is to use same kernel as guest and host.
27 You can configure them differently, but usually it's easiest not to.
Rusty Russell8ca47e02007-07-19 01:49:29 -070028
29 You will need to configure your kernel with the following options:
30
Rusty Russell9653c4a2007-10-22 10:56:23 +100031 "General setup":
32 "Prompt for development and/or incomplete code/drivers" = Y
33 (CONFIG_EXPERIMENTAL=y)
Rusty Russell8ca47e02007-07-19 01:49:29 -070034
Rusty Russell9653c4a2007-10-22 10:56:23 +100035 "Processor type and features":
36 "Paravirtualized guest support" = Y
37 "Lguest guest support" = Y
38 "High Memory Support" = off/4GB
39 "Alignment value to which kernel should be aligned" = 0x100000
40 (CONFIG_PARAVIRT=y, CONFIG_LGUEST_GUEST=y, CONFIG_HIGHMEM64G=n and
41 CONFIG_PHYSICAL_ALIGN=0x100000)
42
43 "Device Drivers":
44 "Network device support"
45 "Universal TUN/TAP device driver support" = M/Y
46 (CONFIG_TUN=m)
47 "Virtualization"
48 "Linux hypervisor example code" = M/Y
49 (CONFIG_LGUEST=m)
Rusty Russell8ca47e02007-07-19 01:49:29 -070050
51- A tool called "lguest" is available in this directory: type "make"
52 to build it. If you didn't build your kernel in-tree, use "make
53 O=<builddir>".
54
55- Create or find a root disk image. There are several useful ones
56 around, such as the xm-test tiny root image at
57 http://xm-test.xensource.com/ramdisks/initrd-1.1-i386.img
58
59 For more serious work, I usually use a distribution ISO image and
60 install it under qemu, then make multiple copies:
61
62 dd if=/dev/zero of=rootfile bs=1M count=2048
63 qemu -cdrom image.iso -hda rootfile -net user -net nic -boot d
64
Rusty Russell9653c4a2007-10-22 10:56:23 +100065 Make sure that you install a getty on /dev/hvc0 if you want to log in on the
66 console!
67
Rusty Russell8ca47e02007-07-19 01:49:29 -070068- "modprobe lg" if you built it as a module.
69
70- Run an lguest as root:
71
Chris Malley1f5a2902007-10-22 11:27:54 +100072 Documentation/lguest/lguest 64 vmlinux --tunnet=192.168.19.1 --block=rootfile root=/dev/vda
Rusty Russell8ca47e02007-07-19 01:49:29 -070073
74 Explanation:
Rusty Russell9653c4a2007-10-22 10:56:23 +100075 64: the amount of memory to use, in MB.
Rusty Russell8ca47e02007-07-19 01:49:29 -070076
77 vmlinux: the kernel image found in the top of your build directory. You
78 can also use a standard bzImage.
79
80 --tunnet=192.168.19.1: configures a "tap" device for networking with this
81 IP address.
82
Chris Malley1f5a2902007-10-22 11:27:54 +100083 --block=rootfile: a file or block device which becomes /dev/vda
Rusty Russell8ca47e02007-07-19 01:49:29 -070084 inside the guest.
85
Chris Malley1f5a2902007-10-22 11:27:54 +100086 root=/dev/vda: this (and anything else on the command line) are
Rusty Russell8ca47e02007-07-19 01:49:29 -070087 kernel boot parameters.
88
89- Configuring networking. I usually have the host masquerade, using
90 "iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE" and "echo 1 >
91 /proc/sys/net/ipv4/ip_forward". In this example, I would configure
92 eth0 inside the guest at 192.168.19.2.
93
94 Another method is to bridge the tap device to an external interface
95 using --tunnet=bridge:<bridgename>, and perhaps run dhcp on the guest
96 to obtain an IP address. The bridge needs to be configured first:
97 this option simply adds the tap interface to it.
98
99 A simple example on my system:
100
101 ifconfig eth0 0.0.0.0
102 brctl addbr lg0
103 ifconfig lg0 up
104 brctl addif lg0 eth0
105 dhclient lg0
106
107 Then use --tunnet=bridge:lg0 when launching the guest.
108
109 See http://linux-net.osdl.org/index.php/Bridge for general information
110 on how to get bridging working.
111
112- You can also create an inter-guest network using
113 "--sharenet=<filename>": any two guests using the same file are on
114 the same network. This file is created if it does not exist.
115
Rusty Russell9653c4a2007-10-22 10:56:23 +1000116There is a helpful mailing list at http://ozlabs.org/mailman/listinfo/lguest
Rusty Russell8ca47e02007-07-19 01:49:29 -0700117
Rusty Russell9653c4a2007-10-22 10:56:23 +1000118Good luck!
Rusty Russell8ca47e02007-07-19 01:49:29 -0700119Rusty Russell rusty@rustcorp.com.au.