Re: [Bug-xorriso] Mountable ISO and GRUB2

[Carlo Caione]

On Fri, Dec 23, 2016 at 3:11 PM, Thomas Schmitt <address@hidden> wrote:

/cut

>> Right now we are generating the GRUB2 eltorito.img with something like:
>> ...
>> This is basically what grub-mkrescue is doing behind the curtain with
>> some customization we need for our setup.
>> ...
>> The problem we have is that the generated ISO doesn't have a mountable
>> ISO partition. In both MBR and GPT the first partition is starting at
>> 512-block 64 instead that 512-block 0.
>
> That's Vladimir Serbinko's preferred layout: GPT with standards compliant
> "Protective MBR".
>
> I myself would prefer the MBR based variant. There is a wrapper script
>   
> https://dev.lovelyhq.com/libburnia/libisoburn/blob/master/frontend/grub-mkrescue-sed.sh
> which given to grub-mkrescue modifies the xorriso arguments so that my
> preferred layout emerges. With installed Debian packages
>   grub-pc-bin, grub-efi-ia32-bin, grub-efi-amd64-bin

This is really interesting. The output MBR is exactly what we were
looking for but IIUC this only creates a Legacy Master Boot Record
(UEFI compliant) mapping the UEFI System Partition but basically it is
not creating the GPT at all. I understand that according to the UEFI
this should be enough for booting BIOS and UEFI systems but I wonder
if that's really enough.

In the Ubuntu and Fedora cases (for example) I clearly see that the
ISO image contains the GPT and also Matthew seems pretty convinced
that GPT is sometimes needed (in
https://mjg59.dreamwidth.org/11285.html, quoting "Why have a GPT at
all? The EFI spec says that machines should boot fine from an MBR
partition. Sadly, not all seem to.").

So, what about GPT? what if we want also to have the GPT in our ISO
image? (with at least ESP and one GPT partition mapping the whole
image)

Thank you,

-- 
Carlo Caione  |  +39.340.80.30.096  |  Endless