Re: [Qemu-devel] [Qemu-ppc] Qemu boot device precedence over nvram boot-device setting

[Gleb Natapov <gleb@redhat.com>]

On Thu, Sep 27, 2012 at 08:21:43PM +1000, Benjamin Herrenschmidt wrote:
> On Thu, 2012-09-27 at 11:51 +0200, Gleb Natapov wrote:
> 
> > Yes, forget about -boot. It is deprecated :) You should use bootindex
> > (device property) to set boot priority. It constructs OF device path
> > and passes it to firmware. There is nothing "blurry" about OF device
> > path. 
> 
> Of course it is ;-) They are perfectly precise down to the device for
> which qemu generates the device-tree ... and from there it requires the
> firmware and qemu to both agree on how they are constructed, and it
> becomes totally unpredictable once things like f-code drivers coming
> from adapter ROMs enter the picture.
> 
If QEMU generates OF device path that can't be used by firmware uniquely
identify the device this is QEMU bug. You are correct about ROMs though.
At least on a PC single ROM can register multiple boot vectors and since
QEMU knows nothing about them it can't prioritize between them. It's sad
if OF has similar problem.

> In fact, we can probably get them right down the the PCI device for PCI
> (for which we don't currently construct the device nodes in qemu, but we
> can 'guess'). And we can probably get the right unit address for vscsi,
> virtio-scsi, etc... but that's about it.
What more do you need?

> 
> > The problem is that it works reasonably well with legacy BIOS
> > since it is enough to specify device to boot from, but with EFI (OF is
> > the same I guess) it is not enough to point to a device to boot from,
> > but you also need to specify a file you want to boot and this is where
> > bootindex approach fails. If EFI would specify default file to boot from
> > firmware could have used it, but EFI specifies it only for removable media
> > (what media is not removable this days, especially with virtualization?).
> > We can add qemu parameter to specify file to boot, but how users should
> > know the name of the file?
> 
> Cheers,
> Ben.
> 
> 

--
			Gleb.