On Mon, Oct 11, 2010 at 12:01:58PM -0500, Anthony Liguori wrote: > On 10/11/2010 10:52 AM, Stefan Hajnoczi wrote: > >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. > > It still registers a BEV entry though, no? > > Does it at least try to boot from the PCI bus/addr/fn of the > selected BEV entry? > I think so. Kevin will know for sure.
-- Gleb.