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Re: [Xen-devel] Discussion: xen hvm guest direct kernel boot

On Fri, Apr 25, 2014 at 01:08:18AM -0600, Chun Yan Liu wrote:
> Hi, 


> I'm looking at xen hvm guest direct kernel boot and interested to do
> it. I found there were some discussions about it and an early work
> around by Daniel (based on xen qemu-dm).
> [1]http://old-list-archives.xenproject.org/xen-devel/2011-08/msg00414.html
> [2]http://old-list-archives.xenproject.org/archives/html/xen-devel/2007-12/msg00723.html
> In xen, the BIOS is provided by hvmloader, which is loaded to RAM in
> libxc. When hvmloader finishes, it jumps to BIOS entry point. BIOS
> will probe for MBR from qemu disk, through grub loading kernel and
> initrd to correct address and then start the guest kernel.
> In [2], the work around implementation is to pass kernel and initrd
> to qemu, qemu reads kernel and initrd to certain address and generate
> a boot sector on the 1st disk for BIOS probing.
> But in current qemu code, the load_linux() way is different. It reads
> kernel and initrd to certain address, then put linuxboot.bin and
> multiboot.bin to option roms which will intercept boot process, so
> that boot process will jump to linuxboot.bin/multiboot.bin instead
> of normal int19 probing MBR stage. This sounds much cleaner then
> generating a boot sector. And in current xen hvmloader, it uses
> seabios, which is also the one upstream qemu uses.
> So, back to xen direct kernel boot, I wonder if not generate a boot
> sector for BIOS probing, could we break hvmloader limitation and
> borrow qemu load_linux() way to achieve the goal? Then, where is the
> right place to load the kernel and initrd, any way to intercept boot
> process? Could we touch hvmloader?
> My knowledge is limited in this part. Welcome experts' clues or ideas
> or discussions. Thanks.

I'm not an expert on this feature, but it sounds like an useful feature to have,
for easier testing of guest kernels etc.

Konrad maybe has some comments/ideas as Xen 4.5 release coordinator.

-- Pasi

> Regards,
> Chunyan

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