Re: [PATCH] x86/Documentation: explain LINUX_EFI_INITRD_MEDIA_GUID

["Hugo Osvaldo Barrera" <hugo@whynothugo.nl>]

On Thu, 11 Sep 2025, at 14:49, Ard Biesheuvel wrote:
> On Thu, 11 Sept 2025 at 13:23, Hugo Osvaldo Barrera <hugo@whynothugo.nl> wrote:
>>
>>
>>
>> On Thu, 11 Sep 2025, at 08:46, Ard Biesheuvel wrote:
>> > On Wed, 10 Sept 2025 at 03:58, Bagas Sanjaya <bagasdotme@gmail.com> wrote:
>> >>
>> >> From: Hugo Osvaldo Barrera <hugo@whynothugo.nl>
>> >>
> ...
>> >> +For sample implementations, refer to `the original u-boot implementation`_ or
>> >> +`the implementation in candyboot`_.
>> >> +
>> >> +.. _the original u-boot implementation: https://github.com/u-boot/u-boot/commit/ec80b4735a593961fe701cc3a5d717d4739b0fd0
>> >> +.. _the implementation in candyboot: https://git.sr.ht/~whynothugo/candyboot/tree/4097b2538d7f1cf85f03922bf42409490b666202/item/src/main.rs#L225
>> >>
>> >
>> > What is candyboot, and why are we adding this plug for it into the
>> > Linux documentation?
>>
>> It's a UEFI stub loader which can load the Linux kernel and provide it with an
>> initramfs using the above described protocol.
>>
>> The original version of this patch was based on my notes researching _how_
>> to implement this stub loader. The implementation is quite minimal, so I think
>> it serves as a useful reference example.
>>
>
> I think one example reference is sufficient, and I think piggybacking
> a plug of your own project onto a documentation refactoring patch is
> slightly dodgy, to be completely honest.

I don't know what kind of reaction you're expecting. The documentation
improvements were a side-effect of developing candyboot. You're free to
exclude the mention if you feel it is inadequate, but I don't appreciate
the personal attack.

> Where is candyboot used, and what does it add to the existing u-boot
> reference, which is the most widely used EFI implementation after EDK2
> for non-x86 systems?

candyboot can be used to produce a single bootable UEFI binary bundling
the kernel, cmdline and initrd. This binary can be signed to boot using
SecureBoot on regular consumer hardware. It is typically useful is
situations where u-boot isn't supported, and useless in most situations
where u-boot is usable.

The use-case is somewhat tangential here; the reference is merely as a
minimal (single file) reference implementation of the feature being
described here.

> If anything, we should be referring to the OVMF implementation here.

Agreed (I didn't know of its existence), here's a link to it:

https://github.com/tianocore/edk2/blob/502f0dfda4f2c4d1cc091f68b6467b6ef12cab45/OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c#L908

-- 
Hugo