xen/stubdom

                                IOEMU stubdom
                                =============

  This boosts HVM performance by putting ioemu in its own lightweight domain.

General Configuration
=====================

Due to a race between the creation of the IOEMU stubdomain itself and allocation
of video memory for the HVM domain, you need to avoid the need for ballooning,
by using the hypervisor dom0_mem= option for instance.


There is a sample configuration set in xmexample.hvm-stubdom

In your HVM config "hvmconfig" use stubdom-dm as dm script:

device_model = 'stubdom-dm'


To run
======

mkdir -p /exports/usr/share/xen/qemu
ln -s /usr/share/xen/qemu/keymaps /exports/usr/share/xen/qemu
mkdir -p /exports/var/lib
ln -s /var/lib/xen /exports/var/lib
/usr/sbin/fs-backend &

xm create hvmconfig



                                   PV-GRUB
                                   =======

  This replaces pygrub to boot domU images safely: it runs the regular grub
inside the created domain itself and uses regular domU facilities to read the
disk / fetch files from network etc. ; it eventually loads the PV kernel and
chain-boots it.
  
Configuration
=============

In your PV config,

- use pv-grub.gz as kernel:

kernel = "pv-grub.gz"

- set the path to menu.lst, as seen from the domU, in extra:

extra = "(hd0,0)/boot/grub/menu.lst"

or you can provide the content of a menu.lst stored in dom0 by passing it as a
ramdisk:

ramdisk = "/boot/domU-1-menu.lst"

or you can also use a tftp path (dhcp will be automatically performed):

extra = "(nd)/somepath/menu.lst"

or you can set it in option 150 of your dhcp server and leave extra and ramdisk
empty (dhcp will be automatically performed)

Limitations
===========

- You can not boot a 64bit kernel with a 32bit-compiled PV-GRUB and vice-versa.
To cross-compile a 32bit PV-GRUB,

export XEN_TARGET_ARCH=x86_32

- bootsplash is supported, but the ioemu backend does not yet support restart
for use by the booted kernel.

- PV-GRUB doesn't support virtualized partitions. For instance:

disk = [ 'phy:hda7,hda7,w' ]

will be seen by PV-GRUB as (hd0), not (hd0,6), since GRUB will not see any
partition table.


                                Your own stubdom
                                ================

  By running

cd stubdom/
make c-stubdom

  or

cd stubdom/
make caml-stubdom

  you can compile examples of C or caml stub domain kernels.  You can use these
and the relevant Makefile rules as basis to build your own stub domain kernel.
Available libraries are libc, libxc, libxs, zlib and libpci.