Re: [Qemu-devel] [PATCH v4 6/7] Make the kernel image in the fw_cfg DMA interface bootable

[Gerd Hoffmann <kraxel@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