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. Stefan
