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Annotation of qemu/docs/bootindex.txt, revision 1.1

1.1     ! root        1: = Bootindex propery =
        !             2: 
        !             3: Block and net devices have bootindex property. This property is used to
        !             4: determine the order in which firmware will consider devices for booting
        !             5: the guest OS. If the bootindex property is not set for a device, it gets
        !             6: lowest boot priority. There is no particular order in which devices with
        !             7: unset bootindex property will be considered for booting, but they will
        !             8: still be bootable.
        !             9: 
        !            10: == Example ==
        !            11: 
        !            12: Lets assume we have QEMU machine with two NICs (virtio, e1000) and two
        !            13: disks (IDE, virtio):
        !            14: 
        !            15: qemu -drive file=disk1.img,if=none,id=disk1
        !            16:      -device ide-drive,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: 
        !            22: Given the command above, firmware should try to boot from the e1000 NIC
        !            23: first.  If this fails, it should try the virtio NIC next, if this fails
        !            24: too, it should try the virtio disk, and then the IDE disk.
        !            25: 
        !            26: == Limitations ==
        !            27: 
        !            28: 1. Some firmware has limitations on which devices can be considered for
        !            29: booting.  For instance, the PC BIOS boot specification allows only one
        !            30: disk to be bootable.  If boot from disk fails for some reason, the BIOS
        !            31: won't retry booting from other disk.  It still can try to boot from
        !            32: floppy or net, though.
        !            33: 
        !            34: 2. Sometimes, firmware cannot map the device path QEMU wants firmware to
        !            35: boot from to a boot method.  It doesn't happen for devices the firmware
        !            36: can natively boot from, but if firmware relies on an option ROM for
        !            37: booting, and the same option ROM is used for booting from more then one
        !            38: device, the firmware may not be able to ask the option ROM to boot from
        !            39: a particular device reliably.  For instance with PC BIOS, if a SCSI HBA
        !            40: has three bootable devices target1, target3, target5 connected to it,
        !            41: the option ROM will have a boot method for each of them, but it is not
        !            42: possible to map from boot method back to a specific target.  This is a
        !            43: shortcoming of PC BIOS boot specification.

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