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| author | Gleb Natapov <gleb@redhat.com> | 2011-01-30 12:29:19 +0200 |
|---|---|---|
| committer | Anthony Liguori <aliguori@us.ibm.com> | 2011-02-01 16:50:44 -0600 |
| commit | 466b58648a7b2ba7edb280b585e0b0c26e3be31e (patch) | |
| tree | 996c4a6dae76ea939bf915fafb59bc8bcf9d040c /docs/bootindex.txt | |
| parent | cf8ce30d03339861a46c31aa44c11279c282f2b0 (diff) | |
| download | qemu-466b58648a7b2ba7edb280b585e0b0c26e3be31e.zip qemu-466b58648a7b2ba7edb280b585e0b0c26e3be31e.tar.gz qemu-466b58648a7b2ba7edb280b585e0b0c26e3be31e.tar.bz2 | |
Add boot index documentation.
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Diffstat (limited to 'docs/bootindex.txt')
| -rw-r--r-- | docs/bootindex.txt | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/docs/bootindex.txt b/docs/bootindex.txt new file mode 100644 index 0000000..16083b3 --- /dev/null +++ b/docs/bootindex.txt @@ -0,0 +1,43 @@ += Bootindex propery = + +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 == + +Lets assume we have QEMU machine with two NICs (virtio, e1000) and two +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 +first. If this fails, it should try the virtio NIC next, if this fails +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 +won't retry booting from other disk. It still can try to boot from +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 +a particular device reliably. For instance with PC BIOS, if a SCSI HBA +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 +shortcoming of PC BIOS boot specification. |