2010/10/11 Gleb Natapov <g...@redhat.com>: > 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?
SeaBIOS may do that but gPXE internally just probes all PCI devices. It does not take advantage of the PCI bus/addr/fn that was passed to the option ROM. A gPXE instance will try booting from each available NIC in sequence. Stefan