Re: [Qemu-devel] [PATCH] x86: Manage BIOS boot menu via command line

[Jan Kiszka <jan.kiszka@siemens.com>]

Anthony Liguori wrote:
> Paul Brook wrote:
>> On Thursday 18 December 2008, Jan Kiszka wrote:
>>  
>>> When booting a guest from the command line, you normally do not need the
>>> interactive boot menu with its 3 s waiting that someone might press F12.
>>> So this patch introduces a mechanism to enable the boot menu only on
>>> demand, ie. when the user provided the command line switch -bootmenu.
>>> This reduces boot times to their original dimension.
>>>
>>> The host-guest interface used here is CMOS RAM byte 0x60. If it is
>>> non-zero, the guest BIOS will skip the F12 delay, keeping the previous
>>> behavior in case the host does not support it. -bootmenu was chosen in
>>> favor of -boot as the syntax of the latter is not easily and cleanly
>>> extensible.
>>>     
>>
>> I'm not sure I believe this. We already support multiple options to
>> -boot so why not just add another one (e.g. "q") that means include
>> the boot menu?
>> i.e. -boot qcad would give the current behaviour.
>>   
> 
> Or -boot cad,prompt=[on|off]

-boot currently takes arbitrary characters from a-z. Adding some
extension means changing a lot of code (the users are unfortunately not
well structured right now). And how to deal with the monitor interface
then? Keep it, extend it? Moreover, how should we express the case of
enabling the boot menu without providing any boot device,
"-boot prompt=on"? Then parsing this will be fun - not impossible, for
sure. But so far I'm looking for a straightforward approach.

> 
>> I've no particular preference whether this is communicated to the bios
>> via the current 0x3d region or via a new byte. It looks like there's a
>> spare bit in byte 0x38 that could be used.
>>   

There are even more bits left in this byte. If CMOS is the final way to
go, I will switch to this.

> 
> Or firmware config since that can be shared with non-x86 targets.

I'm open for the firmware config if you explain to me how state
information is supposed to be transfered from rombios32.c (where the
fw_cfg is evaluated) to some function in rombios.c. Tried this but found
nothing obvious.

Jan

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