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From: Laszlo Ersek <lersek@redhat.com>
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Date: Fri, 2 Oct 2015 15:50:14 +0200
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Subject: Re: [Qemu-devel] [PATCH v4 6/7] Make the kernel image in the fw_cfg
 DMA interface bootable
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To: Kevin O'Connor <kevin@koconnor.net>, Gerd Hoffmann <kraxel@redhat.com>
Cc: "Gabriel L. Somlo" <somlo@cmu.edu>, Stefan Hajnoczi <stefanha@gmail.com>, =?UTF-8?Q?Marc_Mar=c3=ad?= <markmb@redhat.com>, Drew <drjones@redhat.com>, qemu-devel@nongnu.org

On 10/02/15 15:40, Kevin O'Connor wrote:
> On Fri, Oct 02, 2015 at 10:09:17AM +0200, Gerd Hoffmann wrote:
>>> - read four bytes from under the fw_cfg selector QEMU_CFG_KERNEL_SIZE
>>>   (0x0008),
>>> - if it is zero,    return -1 --> no kernel boot requested,
>>> - if it is nonzero, return  0 --> which means "top priority".
>>>
>>> In other words, I agree with:
>>>
>>>> -    option_rom[nb_option_roms].bootindex = 0;
>>>> +    option_rom[nb_option_roms].bootindex = 1;
> 
> The bootindex in QEMU is not visible in the firmware, so if the rest
> of patch 6 is dropped then the above should be dropped as well.
> 
>> Hmm.  That makes the boot order undefined for "qemu -kernel foo -device
>> virtio-blk,drive=bar,bootindex=1" when using an old seabios.  I don't
>> think this is a good idea.
> 
> Wouldn't that make the bootorder undefined everywhere?  What does it
> mean to use -kernel and specify a bootorder?

OVMF & AAVMF look at QEMU_CFG_KERNEL_SIZE first, and process the
bootorder only after. (The kernel boot can fail due to various reasons,
after which it makes sense to start processing the bootorder fw_cfg file.)

Thanks
Laszlo