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[Qemu-devel] Re: [PATCHv2] Support for booting from virtio disks

From: Gleb Natapov
Subject: [Qemu-devel] Re: [PATCHv2] Support for booting from virtio disks
Date: Tue, 11 May 2010 15:31:53 +0300

On Tue, May 11, 2010 at 11:19:07AM +0300, Avi Kivity wrote:
> On 05/10/2010 06:48 PM, Anthony Liguori wrote:
> >On 05/10/2010 03:11 AM, Gleb Natapov wrote:
> >>This patch adds native support for booting from virtio disks to Seabios.
> >>
> >>Signed-off-by: Gleb Natapov<address@hidden>
> >
> >A related problem that I think we need to think about how we solve
> >is indicating to Seabios which device we want to boot from
> >
> >With your patch, a user can select a virtio device explicitly or
> >if they use only one virtio device, it will Just Work.
> >
> >However, if a user uses IDE and virtio, or a user has multiple
> >disks, they cannot select a device via -boot.
> >
> >Is this something we need to address?  I don't think we'd break
> >libvirt if we didn't.
> BIOSes traditionally address this by storing the boot order in RTC
> non-volatile memory, and allow the user to configure the order via a
> menu.  We could do the same (storing the RTC memory in a small disk
> image).
Real BIOS can do that because it enumerates all bootable devices,
attach name for each one of them and then asks user to configure
boot order using names it attached to devices. In our case we
want to provide boot order on qemu command line before BIOS
enumerated devices, so qemu should be able to pass enough information
about boot device so that BIOS can uniquely identify it after it will
discover all bootable devices. bus/device pair can be such thing.

> Alternatively we can seed the order from the command line (-boot
> id1,id2,id3 where id* are some qdev property attached to disks, this
> is more flexible than the current syntax I think).
The problem is how to communicate this order to Seabios.


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