2012-08-10 21:53:02 +02:00
|
|
|
= Bootindex property =
|
2011-01-30 11:29:19 +01:00
|
|
|
|
|
|
|
|
Block and net devices have bootindex property. This property is used to
|
|
|
|
|
determine the order in which firmware will consider devices for booting
|
|
|
|
|
the guest OS. If the bootindex property is not set for a device, it gets
|
|
|
|
|
lowest boot priority. There is no particular order in which devices with
|
|
|
|
|
unset bootindex property will be considered for booting, but they will
|
|
|
|
|
still be bootable.
|
|
|
|
|
|
|
|
|
|
== Example ==
|
|
|
|
|
|
2013-04-09 13:48:19 +02:00
|
|
|
Let's assume we have a QEMU machine with two NICs (virtio, e1000) and two
|
2011-01-30 11:29:19 +01:00
|
|
|
disks (IDE, virtio):
|
|
|
|
|
|
|
|
|
|
qemu -drive file=disk1.img,if=none,id=disk1
|
|
|
|
|
-device ide-drive,drive=disk1,bootindex=4
|
|
|
|
|
-drive file=disk2.img,if=none,id=disk2
|
|
|
|
|
-device virtio-blk-pci,drive=disk2,bootindex=3
|
|
|
|
|
-netdev type=user,id=net0 -device virtio-net-pci,netdev=net0,bootindex=2
|
|
|
|
|
-netdev type=user,id=net1 -device e1000,netdev=net1,bootindex=1
|
|
|
|
|
|
|
|
|
|
Given the command above, firmware should try to boot from the e1000 NIC
|
2013-04-09 13:48:19 +02:00
|
|
|
first. If this fails, it should try the virtio NIC next; if this fails
|
2011-01-30 11:29:19 +01:00
|
|
|
too, it should try the virtio disk, and then the IDE disk.
|
|
|
|
|
|
|
|
|
|
== Limitations ==
|
|
|
|
|
|
|
|
|
|
1. Some firmware has limitations on which devices can be considered for
|
|
|
|
|
booting. For instance, the PC BIOS boot specification allows only one
|
|
|
|
|
disk to be bootable. If boot from disk fails for some reason, the BIOS
|
2013-04-09 13:48:19 +02:00
|
|
|
won't retry booting from other disk. It can still try to boot from
|
2011-01-30 11:29:19 +01:00
|
|
|
floppy or net, though.
|
|
|
|
|
|
|
|
|
|
2. Sometimes, firmware cannot map the device path QEMU wants firmware to
|
|
|
|
|
boot from to a boot method. It doesn't happen for devices the firmware
|
|
|
|
|
can natively boot from, but if firmware relies on an option ROM for
|
|
|
|
|
booting, and the same option ROM is used for booting from more then one
|
|
|
|
|
device, the firmware may not be able to ask the option ROM to boot from
|
2013-04-09 13:48:19 +02:00
|
|
|
a particular device reliably. For instance with the PC BIOS, if a SCSI HBA
|
2011-01-30 11:29:19 +01:00
|
|
|
has three bootable devices target1, target3, target5 connected to it,
|
|
|
|
|
the option ROM will have a boot method for each of them, but it is not
|
|
|
|
|
possible to map from boot method back to a specific target. This is a
|
2013-04-09 13:48:19 +02:00
|
|
|
shortcoming of the PC BIOS boot specification.
|
