130 lines
4.8 KiB
Plaintext
130 lines
4.8 KiB
Plaintext
Rusty's Remarkably Unreliable Guide to Lguest
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- or, A Young Coder's Illustrated Hypervisor
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http://lguest.ozlabs.org
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Lguest is designed to be a minimal hypervisor for the Linux kernel, for
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Linux developers and users to experiment with virtualization with the
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minimum of complexity. Nonetheless, it should have sufficient
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features to make it useful for specific tasks, and, of course, you are
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encouraged to fork and enhance it.
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Features:
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- Kernel module which runs in a normal kernel.
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- Simple I/O model for communication.
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- Simple program to create new guests.
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- Logo contains cute puppies: http://lguest.ozlabs.org
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Developer features:
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- Fun to hack on.
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- No ABI: being tied to a specific kernel anyway, you can change anything.
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- Many opportunities for improvement or feature implementation.
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Running Lguest:
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- Lguest runs the same kernel as guest and host. You can configure
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them differently, but usually it's easiest not to.
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You will need to configure your kernel with the following options:
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CONFIG_HIGHMEM64G=n ("High Memory Support" "64GB")[1]
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CONFIG_TUN=y/m ("Universal TUN/TAP device driver support")
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CONFIG_EXPERIMENTAL=y ("Prompt for development and/or incomplete code/drivers")
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CONFIG_PARAVIRT=y ("Paravirtualization support (EXPERIMENTAL)")
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CONFIG_LGUEST=y/m ("Linux hypervisor example code")
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and I recommend:
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CONFIG_HZ=100 ("Timer frequency")[2]
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- A tool called "lguest" is available in this directory: type "make"
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to build it. If you didn't build your kernel in-tree, use "make
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O=<builddir>".
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- Create or find a root disk image. There are several useful ones
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around, such as the xm-test tiny root image at
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http://xm-test.xensource.com/ramdisks/initrd-1.1-i386.img
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For more serious work, I usually use a distribution ISO image and
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install it under qemu, then make multiple copies:
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dd if=/dev/zero of=rootfile bs=1M count=2048
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qemu -cdrom image.iso -hda rootfile -net user -net nic -boot d
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- "modprobe lg" if you built it as a module.
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- Run an lguest as root:
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Documentation/lguest/lguest 64m vmlinux --tunnet=192.168.19.1 --block=rootfile root=/dev/lgba
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Explanation:
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64m: the amount of memory to use.
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vmlinux: the kernel image found in the top of your build directory. You
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can also use a standard bzImage.
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--tunnet=192.168.19.1: configures a "tap" device for networking with this
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IP address.
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--block=rootfile: a file or block device which becomes /dev/lgba
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inside the guest.
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root=/dev/lgba: this (and anything else on the command line) are
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kernel boot parameters.
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- Configuring networking. I usually have the host masquerade, using
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"iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE" and "echo 1 >
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/proc/sys/net/ipv4/ip_forward". In this example, I would configure
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eth0 inside the guest at 192.168.19.2.
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Another method is to bridge the tap device to an external interface
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using --tunnet=bridge:<bridgename>, and perhaps run dhcp on the guest
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to obtain an IP address. The bridge needs to be configured first:
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this option simply adds the tap interface to it.
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A simple example on my system:
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ifconfig eth0 0.0.0.0
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brctl addbr lg0
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ifconfig lg0 up
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brctl addif lg0 eth0
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dhclient lg0
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Then use --tunnet=bridge:lg0 when launching the guest.
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See http://linux-net.osdl.org/index.php/Bridge for general information
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on how to get bridging working.
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- You can also create an inter-guest network using
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"--sharenet=<filename>": any two guests using the same file are on
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the same network. This file is created if it does not exist.
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Lguest I/O model:
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Lguest uses a simplified DMA model plus shared memory for I/O. Guests
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can communicate with each other if they share underlying memory
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(usually by the lguest program mmaping the same file), but they can
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use any non-shared memory to communicate with the lguest process.
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Guests can register DMA buffers at any key (must be a valid physical
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address) using the LHCALL_BIND_DMA(key, dmabufs, num<<8|irq)
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hypercall. "dmabufs" is the physical address of an array of "num"
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"struct lguest_dma": each contains a used_len, and an array of
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physical addresses and lengths. When a transfer occurs, the
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"used_len" field of one of the buffers which has used_len 0 will be
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set to the length transferred and the irq will fire.
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Using an irq value of 0 unbinds the dma buffers.
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To send DMA, the LHCALL_SEND_DMA(key, dma_physaddr) hypercall is used,
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and the bytes used is written to the used_len field. This can be 0 if
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noone else has bound a DMA buffer to that key or some other error.
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DMA buffers bound by the same guest are ignored.
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Cheers!
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Rusty Russell rusty@rustcorp.com.au.
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[1] These are on various places on the TODO list, waiting for you to
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get annoyed enough at the limitation to fix it.
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[2] Lguest is not yet tickless when idle. See [1].
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