linux-kernel - Re: [PATCH] x86/Documentation: explain LINUX_EFI_INITRD_MEDIA

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Message-ID: <0C55A642-8BC8-4C19-9FF5-8B803E2CCABA@zytor.com>
Date: Wed, 10 Sep 2025 13:09:50 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Bagas Sanjaya <bagasdotme@...il.com>, Randy Dunlap <rdunlap@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Documentation <linux-doc@...r.kernel.org>,
        Linux EFI <linux-efi@...r.kernel.org>
CC: Ard Biesheuvel <ardb@...nel.org>, Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Hugo Osvaldo Barrera <hugo@...nothugo.nl>
Subject: Re: [PATCH] x86/Documentation: explain LINUX_EFI_INITRD_MEDIA_GUID

On September 9, 2025 11:01:54 PM PDT, Bagas Sanjaya <bagasdotme@...il.com> wrote:
>On Tue, Sep 09, 2025 at 08:25:34PM -0700, Randy Dunlap wrote:
>> On 9/9/25 6:57 PM, Bagas Sanjaya wrote:
>> > +.. _pe-coff-entry-point:
>> > +
>> > +PE/COFF entry point
>> > +===================
>> > +
>> > +When compiled with ``CONFIG_EFI_STUB=y``, the kernel can be executed as a
>> > +regular PE/COFF binary. See Documentation/admin-guide/efi-stub.rst for
>> > +implementation details.
>> > +
>> > +The stub loader can request the initrd via a UEFI protocol. For this to work,
>> > +the firmware or bootloader needs to register a handle which implements the
>> > +``EFI_LOAD_FILE2`` protocol with the ``LINUX_EFI_INITRD_MEDIA_GUID`` device
>> > +path. In this case, a kernel booting via the EFI stub will use the ``LoadFile``
>> > +function on the registered handle to obtain a reference to the initrd.
>> 
>> drivers/firmware/efi/libstub/efi-stub-helper.c (line 509) says LoadFile2
>> protocol. Is that the same as the LoadFile function?
>> 
>> https://github.com/u-boot/u-boot/commit/ec80b4735a593961fe701cc3a5d717d4739b0fd0
>> (the link below) also says LoadFile2() 4 times (and LoadFile 0 times).
>
>>From UEFI spec [1], both LoadFile and LoadFile2 protocol versions of LoadFile()
>function has same prototype but somewhat different in behavior. To answer
>your question, however, I think so.
>
>EFI folks, what are your opinions?
>
>Thanks.
>
>[1]: https://uefi.org/specs/UEFI/2.10/13_Protocols_Media_Access.html
>

Sounds like the code was updated but not the documentation.