[SeaBIOS] [Qemu-devel] [RFC] Passing boot order from qemu to seabios

[Stefan Hajnoczi]

On Mon, Oct 11, 2010 at 12:16 PM, Bernhard Kohl <bernhard.kohl at nsn.com> wrote:
> Am 11.10.2010 12:18, schrieb ext Gleb Natapov:
>>
>> Currently if VM is started with multiple disks it is almost impossible to
>> guess which one of them will be used as boot device especially if there
>> is a mix of ATA/virtio/SCSI devices. Essentially BIOS decides the order
>> and without looking into the code you can't tell what the order will
>> be (and in qemu-kvm if boot=on is used it brings even more havoc). We
>> should allow fine-grained control of boot order from qemu command line,
>> or as a minimum control what device will be used for booting.
>>
>> To do that along with inventing syntax to specify boot order on qemu
>> command line we need to communicate boot order to seabios via fw_cfg
>> interface. For that we need to have a way to unambiguously specify a
>> disk from qemu to seabios.  PCI bus address is not enough since not all
>> devices are PCI (do we care about them?) and since one PCI device may
>> control more then one disk (ATA slave/master, SCSI LUNs). We can do what
>> EDD specification does. Describe disk as:
>>     bus type (isa/pci),
>>     address on a bus (16 bit base address for isa, b/s/f for pci)
>>     device type (ATA/SCSI/VIRTIO)
>>     device path (slave/master for ATA, LUN for SCSI, nothing for virtio)
>>
>> Will it cover all use cased? Any other ideas?
>
> I think this also applies to network booting via gPXE. Usually our VMs
> have 4 NICs, mixed virtio-net and PCI pass-through. 2 of the NICs shall
> be used for booting, even if there are hard disks or floppy disks
> connected. This scenario is currently almost impossible to configure.

Here is a gPXE to support fw_cfg.  You can pass gPXE script files from
the host to gPXE inside the guest.  This means you can boot specific
NICs:
http://patchwork.ozlabs.org/patch/43777/

Just wanted to post the link because it is related to the gPXE side of
this discussion.

Stefan