Re: UEFI corner case we don't handle yet - dual-boot with non-UEFI Windows
On 11 February 2014 01:01, Steve McIntyre <steve@einval.com> wrote:
> Gah...
>
> Just ended up playing with Colin's thinkpad; he'd reported problems
> with installation that sounded odd. Worked through it, and found a
> hole in what we recognise and support during installation (and maybe
> later).
>
> We have a machine with both UEFI and BIOS-mode boot available, with an
> existing BIOS-mode Windows installation (e.g. Windows 7 in this case)
> *but* the machine is set up to try and boot UEFI first and *then* fall
> back to BIOS (for some reason).
>
> The existing Windows installation boots via the fallback, and the user
> has no reason to ever investigate this. However, d-i will happily boot
> in UEFI mode. When we get to partitioning, there is no EFI System
> Partition (ESP), as Windows isn't using one. We then get to either of
> two potentially bad cases:
>
> (a) the user shuffles partitions around and makes an ESP, installs
> the system OK including grub-efi. They then have a machine that
> will boot via UEFI to grub, but maybe will not be able to boot
> Windows. I've not tested this directly yet, but I can see this
> happening. To get to their existing Windows installation, the
> user will have to switch boot mode in the firmware setup - bad.
>
> (b) the user does not make an ESP, installs a system but grub-efi
> fails to install properly for that reason. I'm seeing bug reports
> that suggest this path does *not* necessarily give a clear error
> to the user, maybe in some cases no error at all. They reboot
> their newly-installed system and find it immediately goes into
> Windows with no sign of their new Debian installation at all.
>
> How do we fix this? I think we need to find some way of detecting how
> an existing Windows installation boots, *iff* the user is clearly
> trying to set up a dual-boot system. If the existing Windows
> installation is in BIOS-mode, we should *not* follow the UEFI path
> through partitioning and bootloader installation; instead, we should
> fall back to the existing generic/BIOS cases in various places. I
> don't see this being *easy* to do, but there aren't many code paths to
> worry about AFAIK.
>
> What do people think?
As a data point, a few bug reports in Ubuntu were also filed about
similar behavior. A metabug is probably
https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1050940
(note that the bug there is quite vocal)
I don't now the right answer here. But e.g. my motherboard has
configuration options to choose priority of UEFI vs BIOS boot for all
device types, such that it can do BIOS-only on removable media / usb
sticks, but UEFI on the hard-drives =) but i guess it's users fault
for changing non-default firmware settings.
It seems however, that "existing BIOS installation" is a common enough
case to warrant support for ( it doesn't have to be Windows7, it could
also be other operating systems expecting bios boot).
--
Regards,
Dimitri.
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