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.
I already posted a patch 'new parameter boot=on|off for "-net nic" and "-device" NIC devices' which should solve that problem for us. The patch is still under discussion. Of course passing detailed boot device information to SeaBIOS would be the best solution.
Any ideas about qemu command line syntax? May be somebody whats to implement it? :)
-- Gleb.