On Mon, Oct 11, 2010 at 05:42:30PM +0200, Avi Kivity wrote: > On 10/11/2010 05:39 PM, Gleb Natapov wrote: > >On Mon, Oct 11, 2010 at 05:09:22PM +0200, Avi Kivity wrote: > >> On 10/11/2010 12:18 PM, Gleb Natapov wrote: > >> >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? Any ideas about qemu > >> >command line syntax? May be somebody whats to implement it? :) > >> > >> Instead of fwcfg, we should store the boot order in the bios. This > >> allows seabios to implement persistent boot selection and control > >> boot order from within the guest. > >> > >It is not "instead of" it is in a best case "in addition too". First of > >all seabios does not have persistent storage currently and second I much > >prefer specifying boot device from command line instead of navigating > >bios menus. That what we have to do on real HW because there is not > >other way to do it, but in virtualization we can do better. > > Ok. So fwcfg will have an option "do your default thing" which the > bios can take as a hint to look in cmos memory. > Definitely. If qemu does not provide any info about boot order default logic should be used.
-- Gleb.