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

Kevin Wolf kwolf at redhat.com
Mon Oct 11 12:32:48 CEST 2010

Am 11.10.2010 12:18, schrieb 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?) 

Floppy? Yes, I think we do.

> 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)

If we had a qdev ID for all devices (which I think we should have
anyway), would this work or is a string not really handy enough?


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