On Mon, Oct 11, 2010 at 01:48:09PM +0100, Stefan Hajnoczi wrote: > On Mon, Oct 11, 2010 at 12:16 PM, Bernhard Kohl <bernhard.k...@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. > Don't we load gPXE for each NIC and seabios passes PCI device to boot from when it invokes one of them?
-- Gleb.