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Re: Adding option to clearpart in kickstart to not set pmbr_boot flag?



On Sat, Jul 03, 2021 at 08:36:54AM -0400, Neal Gompa wrote:
> Hey all,
> 
> As a follow up to Chris' thread on hybrid BIOS/UEFI images[1], it was
> pointed out that in order to build images that actually boot, I need
> to make sure that the protective MBR boot flag isn't set. To implement
> this for Fedora Cloud images, I'm using parted in %post[2]. However,
> that has a major problem: I don't necessarily know what the block
> device name is going to be. I'm making an educated guess, but for
> third parties attempting to rebuild our images, that guess may be
> wrong.
> 
> What I'd like to see is the clearpart command getting a
> --no-gpt-pmbr-boot-flag or similar that would allow me to do this
> without having to write a magic snippet that includes a guess on how
> this works.
> 
> I imagine this would also be useful for RHEL/CentOS 9, since it would
> simplify making hybrid boot images.
> 
> What do y'all think?

I really don't want to add new flags to pykickstart for every corner
case, so I think this needs to be fixed some other way.

blivet is what's actually responsible for setting this, see:

https://github.com/storaged-project/blivet/blob/98e436074345974ab1f793f521f0483bdb6d3ba9/blivet/formats/disklabel.py#L187

so changing that isn't a simple change.

If I understand the issue, it's that KVM's UEFI firmware isn't booting
with this set? This seems strange, since it looks like pmbr_boot is
always set by blivet for non-mac UEFI installs, and it has been this way
for a considerable amount of time.

More importantly, the UEFI specification specifically states that UEFI
firmware is to ignore the flag (it's called 'BootIndicator' in the
spec) so if the firmware isn't recognizing it because of that flag it is
a bug.

Brian

-- 
Brian C. Lane (PST8PDT) - weldr.io - lorax - parted - pykickstart


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