Re: [Xen-users] vanilla kernel and xen (in general), ?vanilla 2.6.24 and xen

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Sun, Feb 03, 2008 at 03:59:10AM +0000, Mark Williamson wrote:
> > >> There shall be nothing special. Take a config for 2.6.18 kernel and just
> > >> change the kernel and initrd lines. as long as the build is matching the
> > >> Xen capability, PAE nonPAE etc.
> > >
> > > The Xen code that's in 2.6.24 from kernel.org is rather different to that
> > > in 2.6.18 XenLinux from XenSource.  So just reusing the same config file
> > > will probably not work on its own, sorry :-(
> >
> > Can you comment on that a bit more? Are there now like 2 different
> > branches of kernel Xen for a domain user?
> 
> Essentially, yes.
> 
> The XenLinux kernel which XenSource hosts and develops and that is the basis 
> of the existing distro kernels is based on a source tree whose history dates 
> back to the really early days of Xen.  This has full support for all the cool 
> bits of functionality Xen supports and can run as dom0 or domU; however it 
> can't be booted as a "native" kernel on bare-metal and it's based on the 
> 2.6.18 kernel, which is getting old.
> 
> kernel.org Linux has support for running as a Xen domU since Linux 2.6.23 was 
> released.  The Xen-aware code in that is derived from that in the XenSource 
> XenLinux kernel - in many places it's a port of the same code, not a 
> different implementation.  However, quite a lot of changes were required to 
> make the addition of Xen support acceptable to the mainline kernel developers 
> (using paravirt-ops) to the XenLinux 2.6.18 (which uses a separate Xen 
> subarchitecture).  Jeremy Fitzhardinge at XenSource took on the difficult 
> task of getting Xen support in mainline Linux and managed to get a basic set 
> of functionality merged into 2.6.23.
> 
> The current situation is still not ideal, since the XenLinux kernel is still 
> based on 2.6.18 and it's hard work for distros to forward-port Xen support to 
> whatever kernel they're running.  Meanwhile the kernel.org port doesn't 
> support all the juicy features that XenLinux 2.6.18 supports.
> 
> A number of people - Red Hat are helping spearhead this - are working on 
> turning all the juicy features of XenLinux 2.6.18 into patches on top of 
> mainline Linux's existing Xen support.  This includes support for running as 
> dom0.
> 
> The end goal, I believe, is to get as much Xen support upstream as possible 
> (e.g. paravirt framebuffer, live migration support, maybe dom0 support).  
> Anything that's left can be maintained by the Xen developers as a patch on 
> top of mainline linux, rather than maintaining their own separate kernel.
> 
> This involves some short term pain but the end result should be that Xen 
> support is available for newer kernels quicker, kernel.org Linux will come 
> with more Xen functionality by default, and it may even be possible for 
> distros to ship the same kernel for use as the native kernel, as dom0 and as 
> domU (and for lguest, and for VMI).  Which would be awesome :-)
> 
> Does that clear things up a bit?
> 

Upcoming Fedora 9 (from RedHat) should have "full" Xen support in 2.6.24+ 
kernel,
in a form that it can be sent/submitted upstream for inclusion in kernel.org 
vanilla
kernel.

RedHat people are working on this. There have been some mails about the
progress on xen-devel list. 

-- Pasi

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