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1 | Rusty's Remarkably Unreliable Guide to Lguest |
2 | - or, A Young Coder's Illustrated Hypervisor | |
3 | http://lguest.ozlabs.org | |
4 | ||
5 | Lguest is designed to be a minimal hypervisor for the Linux kernel, for | |
6 | Linux developers and users to experiment with virtualization with the | |
7 | minimum of complexity. Nonetheless, it should have sufficient | |
8 | features to make it useful for specific tasks, and, of course, you are | |
9653c4af | 9 | encouraged to fork and enhance it (see drivers/lguest/README). |
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10 | |
11 | Features: | |
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 | ||
18 | Developer 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 | ||
24 | Running Lguest: | |
25 | ||
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26 | - 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. | |
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28 | |
29 | You will need to configure your kernel with the following options: | |
30 | ||
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31 | "General setup": |
32 | "Prompt for development and/or incomplete code/drivers" = Y | |
33 | (CONFIG_EXPERIMENTAL=y) | |
34 | ||
35 | "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) | |
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50 | |
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 | ||
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65 | Make sure that you install a getty on /dev/hvc0 if you want to log in on the |
66 | console! | |
67 | ||
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68 | - "modprobe lg" if you built it as a module. |
69 | ||
70 | - Run an lguest as root: | |
71 | ||
1f5a2902 | 72 | Documentation/lguest/lguest 64 vmlinux --tunnet=192.168.19.1 --block=rootfile root=/dev/vda |
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73 | |
74 | Explanation: | |
9653c4af | 75 | 64: the amount of memory to use, in MB. |
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76 | |
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 | ||
1f5a2902 | 83 | --block=rootfile: a file or block device which becomes /dev/vda |
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84 | inside the guest. |
85 | ||
1f5a2902 | 86 | root=/dev/vda: this (and anything else on the command line) are |
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87 | 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 | ||
9653c4af | 112 | There is a helpful mailing list at http://ozlabs.org/mailman/listinfo/lguest |
8ca47e00 | 113 | |
9653c4af | 114 | Good luck! |
8ca47e00 | 115 | Rusty Russell rusty@rustcorp.com.au. |