1= Bootindex property = 2 3Block and net devices have bootindex property. This property is used to 4determine the order in which firmware will consider devices for booting 5the guest OS. If the bootindex property is not set for a device, it gets 6lowest boot priority. There is no particular order in which devices with 7unset bootindex property will be considered for booting, but they will 8still be bootable. 9 10== Example == 11 12Let's assume we have a QEMU machine with two NICs (virtio, e1000) and two 13disks (IDE, virtio): 14 15qemu -drive file=disk1.img,if=none,id=disk1 16 -device ide-hd,drive=disk1,bootindex=4 17 -drive file=disk2.img,if=none,id=disk2 18 -device virtio-blk-pci,drive=disk2,bootindex=3 19 -netdev type=user,id=net0 -device virtio-net-pci,netdev=net0,bootindex=2 20 -netdev type=user,id=net1 -device e1000,netdev=net1,bootindex=1 21 22Given the command above, firmware should try to boot from the e1000 NIC 23first. If this fails, it should try the virtio NIC next; if this fails 24too, it should try the virtio disk, and then the IDE disk. 25 26== Limitations == 27 281. Some firmware has limitations on which devices can be considered for 29booting. For instance, the PC BIOS boot specification allows only one 30disk to be bootable. If boot from disk fails for some reason, the BIOS 31won't retry booting from other disk. It can still try to boot from 32floppy or net, though. 33 342. Sometimes, firmware cannot map the device path QEMU wants firmware to 35boot from to a boot method. It doesn't happen for devices the firmware 36can natively boot from, but if firmware relies on an option ROM for 37booting, and the same option ROM is used for booting from more then one 38device, the firmware may not be able to ask the option ROM to boot from 39a particular device reliably. For instance with the PC BIOS, if a SCSI HBA 40has three bootable devices target1, target3, target5 connected to it, 41the option ROM will have a boot method for each of them, but it is not 42possible to map from boot method back to a specific target. This is a 43shortcoming of the PC BIOS boot specification. 44 45== Mixing bootindex and boot order parameters == 46 47Note that it does not make sense to use the bootindex property together 48with the "-boot order=..." (or "-boot once=...") parameter. The guest 49firmware implementations normally either support the one or the other, 50but not both parameters at the same time. Mixing them will result in 51undefined behavior, and thus the guest firmware will likely not boot 52from the expected devices. 53