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From: Gerd Hoffmann <kraxel@redhat.com>
Date: Mon, 05 Oct 2015 11:26:04 +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>
Cc: Drew <drjones@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, "Gabriel L. Somlo" <somlo@cmu.edu>, qemu-devel@nongnu.org, Marc =?ISO-8859-1?Q?Mar=ED?= <markmb@redhat.com>, Laszlo Ersek <lersek@redhat.com>

On Fr, 2015-10-02 at 09:40 -0400, 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?

Kernel gets priority 0, everything else what you specify (typically
configs start with bootindex=1), so the kernel gets the highest
priority.  So unless the user uses F12 to enter the boot menu and picks
something else the kernel is booted.

cheers,
  Gerd