Xen dom0, hypervisor

Now that GNU Mach handles PAE you can use a PAE-enabled hypervisor.

You can either get binaries at http://youpibouh.thefreecat.org/hurd-xen/ or build them yourself.

• Copy gnumach-xen-pae and hurd-modules to your dom0 /boot. If you still have a non-PAE hypervisor, use gnumach-xen-nonpae instead.
• Copy hurd into /etc/xen, edit it for fixing access to your hurd / and swap

GNU/Hurd system

You need an already installed GNU/Hurd system.

If you have a free partition, you can fdisk to type 0x83, create a filesystem using:

sudo mke2fs -b 4096 -I 128 -o hurd /dev/sda4 

Replace /dev/sda4 with your partition. Install and use crosshurd to setup a GNU/Hurd system on this partition.

/etc/xen/hurd configuration

Here is a sample /etc/xen/hurd configuration

kernel = "/boot/gnumach-xen-pae"
memory = 256
disk = ['phy:sda4,hda,w']
extra = "root=device:hd0"
vif = [ '' ]
ramdisk = "/boot/hurd-modules"

Do not give more than 580MB memory (due to bootstrap limitations, it's not easy to map more).

Suggestions about networking configuration are available.

If you need stable MAC addresses, use a syntax like vif = [ 'mac=00:16:3e:XX:XX:XX, bridge=br0' ].

Running Hurd with Xen

To run Hurd with Xen, use:

xm create -c hurd

and gnumach should get started. Proceed with native-install.

export TERM=mach
./native-install

• If xm complains about networking (vif could not be connected), it's Xen scripts' fault, see Xen documentation for how to configure the network. The simplest way is network-bridge with fixed IPs (note that you need the bridge-utils package for this). You can also just disable networking by commenting the vif line in the config.
• If xm complains Error: (2, 'Invalid kernel', 'xc_dom_compat_check: guest type xen-3.0-x86_32 not supported by xen kernel, sorry\n'), you most probably have a PAE-enabled hypervisor and a non-PAE gnumach. Either install and boot non-PAE hypervisor and kernel, or rebuilt gnumach in PAE mode.

Building from sources

If you want to generate these images, first get the gnumach-1-branch-Xen-branch branch from gnumach CVS. Then look for "Ugly" in kern/bootstrap.c, how to generate hurd-modules is explained there, and you'll have to fix EXT2FS_SIZE and LD_SO_SIZE by hand. Then use

./configure --enable-platform=xen
make

The current hurd-modules was built from the debian packages hurd 20070606-2 and libc0.3 2.6.1-1. This means that when using this image, your GNU/Hurd system also needs to be a glibc version 2.6 or later-based one!

pv-grub

From Xen 4.0 on you can run the GNU Hurd directly using pv-grub, without the need to prepare a special bootstrap image (like an initrd).

Download http://youpibouh.thefreecat.org/hurd-xen/pv-grub.gz into /boot, and use the following for instance:

kernel = "/boot/pv-grub.gz"
memory = 256
disk = ['phy:sda4,hda,w']
extra = "(hd0,1)/boot/grub/menu.lst"
vif = [ '' ]

extra is now the path to the grub config file.

Partitions

You will need the following notation for the gnumach root= parameter:

root=part:2:device:hd0

to access the second partition of hd0, for instance.

You will also need to use the parted storeio module for the /dev entries, for instance:

settrans -fgap /dev/hd0s1 /hurd/storeio -T typed part:1:device:hd0

Miscellaneous

Internals.

GNU Savannah task #5468, GNU Savannah task #6584.

Host-side Writeback Caching

Optimization possible as it is with QEMU, Host-side Writeback Caching?

IRC, freenode, #hurd, 2011-06-08

<braunr> youpi: does xen provide disk caching options ?
<youpi> through a blktap, probably
<braunr> ok