[SeaBIOS] [RFC] Passing boot order from qemu to seabios

[Avi Kivity]

  On 10/11/2010 12:18 PM, Gleb Natapov wrote:
> 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? Any ideas about qemu
> command line syntax? May be somebody whats to implement it? :)

Instead of fwcfg, we should store the boot order in the bios.  This 
allows seabios to implement persistent boot selection and control boot 
order from within the guest.

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