linux-kernel - Re: [PATCH] initrd: Remove erroneous comment

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Date:   Mon, 22 Jun 2020 13:48:45 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Tom Rini <trini@...sulko.com>, ron minnich <rminnich@...il.com>
Cc:     lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...e.de>,
        Dominik Brodowski <linux@...inikbrodowski.net>
Subject: Re: [PATCH] initrd: Remove erroneous comment

On 2020-06-22 13:40, Tom Rini wrote:
> On Mon, Jun 22, 2020 at 01:02:16PM -0700, ron minnich wrote:
> 
>> The other thing you ought to consider fixing:
>> initrd is documented as follows:
>>
>>         initrd=         [BOOT] Specify the location of the initial ramdisk
>>
>> for bootloaders only.
>>
>> UEFI consumes initrd from the command line as well. As ARM servers
>> increasingly use UEFI, there may be situations in which the initrd
>> option doesn't make its way to the kernel? I don't know, UEFI is such
>> a black box to me. But I've seen this "initrd consumption" happen.
>>
>> Based on docs, and the growing use of bootloaders that are happy to
>> consume initrd= and not pass it to the kernel, you might be better off
>> trying to move to the new command line option anyway.
>>
>> IOW, this comment may not be what people want to see, but ... it might
>> also be right. Or possibly changed to:
>>
>> /*
>>  * The initrd keyword is in use today on ARM, PowerPC, and MIPS.
>>  * It is also reserved for use by bootloaders such as UEFI and may
>>  * be consumed by them and not passed on to the kernel.
>>  * The documentation also shows it as reserved for bootloaders.
>>  * It is advised to move to the initrdmem= option whereever possible.
>>  */
> 
> Fair warning, one of the other hats I wear is the chief custodian of the
> U-Boot project.
> 
> Note that on most architectures in modern times the device tree is used
> to pass in initrd type information and "initrd=" on the command line is
> quite legacy.
> 
> But what do you mean UEFI "consumes" initrd= ?  It's quite expected that
> when you configure grub/syslinux/systemd-boot/whatever via extlinux.conf
> or similar with "initrd /some/file" something reasonable happens to
> read that in to memory and pass along the location to Linux (which can
> vary from arch to arch, when not using device tree).  I guess looking at 
> Documentation/x86/boot.rst is where treating initrd= as a file that
> should be handled and ramdisk_image / ramdisk_size set came from.  I do
> wonder what happens in the case of ARM/ARM64 + UEFI without device tree.
> 

UEFI plus the in-kernel UEFI stub is, in some ways, a "bootloader" in
the traditional sense. It is totally fair that we should update the
documentation with this as a different case, though, because it is part
of the kernel tree and so the kernel now has partial ownership of the
namespace.

I suggest "STUB" for "in-kernel firmware stub" for this purpose; no need
to restrict it to a specific firmware for the purpose of namespace
reservation.

	-hpa