Re: [Xen-users] usage questions for GRUB2 chainloader workaround when booting Xen 4.5 on UEFI

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-03-30 at 06:42 -0700, lyndat3@xxxxxxxxxxxxx wrote:
>       .../efi/xen/xen.efi
> 
> is a bit off as the actual path is
> 
>       .../EFI/XEN/xen.efi
> 
> I do not know yet about grub vs linux case sensitivity in path names.

The underlying filesystem on an ESP is VFAT, so not case sensitive.


> In any case, I now have a recognized root to play with; will work on the rest.
> 
> > Since you are chainloading you might find it easier to put Xen in
> > your /boot rather than on you ESP, since all the existing stanzas will
> > be tailored towards loading stuff from /boot.
> 
> IIUC for the mobo bios to find EFI files for constructing the @ EUFI
> boot menu they must be on an/the EFI, vfat-formatted partition.  I
> haven't tested this, just my understanding atm.

That's true if the BIOS is doing the loading, since the BIOS is only
required by the UEFI spec to be able to access a FAT filesystem.

However grub is capable of reading from a much wider variety of
filesystems, so if you are loading Xen via grub you are not constrained
by that.

> > Lastly, I'm not 100% sure if chainloading xen.efi like this is supposed
> > to work. The docs talk about adding it directly to the UEFI boot menu
> > not going via grub. I suppose the answer depends on what state chainload
> > leaves UEFI in (i.e. boot services still enabled or not).
> 
> Which particular docs are you referring to?

http://xenbits.xen.org/docs/unstable/misc/efi.html which mentions
booting as an "EFI application", which I took to mean "directly from the
BIOS" as opposed to via grub, I may have been wrong to do so though.

The author of the wiki page you've been looking at is someone I trust to
know what they are talking about on this matter, so you should probably
ignore my "Lastly, ..." comment.

>       >       (2) IIUC, since the Xen pkgs are not installing xen.efi on the 
> EFI partion, at every Xen upgrade
>       >           the xen.efi has to be re-copied.  Correct?  Shouldn't pkgs 
> install the .efi on the UEFI system partition?
> 
> leaves me to wonder if pkg-ing is expecting something different.

Not sure what you mean, but it would be expected that a distro package
which wished to support Xen EFI boot would either set EFI_VENDOR and
package the result or otherwise arrange for xen.efi to end up on the
ESP.

Xen EFI is not well integrated into most distros these days though, so
I'd not be surprised if it was all a bit manual.

Ian.


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