Re: [Qemu-devel] [PATCH 0/2] extboot reloaded.

[Kevin O'Connor]

On Mon, Nov 16, 2009 at 03:14:33PM -0600, Anthony Liguori wrote:
> Gerd Hoffmann wrote:
>> Huh?  Do you want export *all* block devices via extboot?  Will IDE  
>> drives show up twice then?
>
> No, because SeaBIOS already has an ATA driver so we wouldn't want to  
> expose IDE on the extboot bus.

One possibility would be for QEMU to tell the bios the type of each
"extboot" drive - that way seabios could ignore drives it already had
native drivers for.

>> I would export only one and export it only on explicit user request,  
>> so it can be used for cases where seabios has no native support ...
>
> If we expose all of the disks, then the user can choose which one they  
> want to boot from without having to shut down qemu and modify the  
> command line.
>
> It's not obvious to me how we could control the position in the IPL  
> table of each disk though.  I guess we could have a priority parameter  
> that was part of the disk enumeration that controlled how each device  
> was added in the table.  Do you have any thoughts Kevin?

Adding to the BCV list is done via the add_bcv_internal() call in
src/boot.c.  The list order is determined by the type of drive and its
internal id - usually drives are arranged in the list in the order
they are found.

The order of hard drives is determined by the BCV list.  There is only
one entry in the IPL table for booting from a hard drive - selecting
"-boot c" prioritizes this IPL - hard drive booting always boots from
the "C" drive.  It's possible to tell SeaBIOS to map the C drive to
something other than the first item on the BCV list, but that
functionality is currently only available via the boot menu.

As an aside, I'm open to adding both an "extboot" driver and
additional native drivers to SeaBIOS.  Both have their uses.

-Kevin