On Mon, Oct 11, 2010 at 12:18:55PM +0200, 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)
That makes sense to me. We could update SeaBIOS to give a short unique name to every BEV and BCV it finds based on the path to the device. (For example, something like "a...@01:1...@0", "u...@1234:5678", "vir...@01:13.0", "r...@01:13.0".) Then qemu could pass in (via fw_cfg) a list of names that the user wishes to boot from. SeaBIOS can then prioritizes those devices it finds that are also in the fw_cfg list. > Will it cover all use cased? Any other ideas? Any ideas about qemu > command line syntax? May be somebody whats to implement it? :) As for qemu command line - maybe just use the current ",boot=on" syntax, and have qemu map it into a "path name" for seabios? -Kevin
