Re: [Buildroot] [PATCH 01/16] board/aarch64-efi/genimage-efi: convert partition-type-uuid to single letter notation

From: "Yann E. MORIN" <yann.morin.1998@free.fr>
To: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Sergey Matyukevich <geomatsi@gmail.com>,
	Alistair Francis <alistair@alistair23.me>,
	Gerome Burlats <gerome.burlats@smile.fr>,
	Jagan Teki <jagan@amarulasolutions.com>,
	Suniel Mahesh <sunil@amarulasolutions.com>,
	Giulio Benetti <giulio.benetti@benettiengineering.com>,
	buildroot@buildroot.org, Romain Naour <romain.naour@gmail.com>
Subject: Re: [Buildroot] [PATCH 01/16] board/aarch64-efi/genimage-efi: convert partition-type-uuid to single letter notation
Date: Mon, 7 Feb 2022 18:37:51 +0100	[thread overview]
Message-ID: <20220207173751.GA2249818@scaer> (raw)
In-Reply-To: <20220207085517.5c13c097@windsurf>

Thomas, All,

On 2022-02-07 08:55 +0100, Thomas Petazzoni spake thusly:
> On Sun, 6 Feb 2022 22:36:57 +0100
> "Yann E. MORIN" <yann.morin.1998@free.fr> wrote:
> > >  	partition root {
> > > -		partition-type-uuid = b921b045-1df0-41c3-af44-4c6f280d3fae
> > > +		partition-type-uuid = L  
> > As we discussed on IRC, this is not the same thing. genimage will extend
> > the 'L' shorthand to the full UUID 0fc63daf-8483-4772-8e79-3d69d8477de4,
> > which is different.
> And? Is that really important?
> > So I don't think uaing the shorthands are correct.
> Why?

I think that it is important that we do adhere to the expected values;
see below...

> > The UUID assignments are available on Wikipedia:
> >     https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_type_GUIDs
> > But the systemd docuemntation has extra UUID definitions:
> >     https://man.archlinux.org/man/systemd-gpt-auto-generator.8
> Yes, but how useful are they?

Why would we diverge from the specs?

> Unless these systemd-defined UUID are really relevant, I would prefer
> that we use the shortcuts provided by genimage wherever possible, and
> only rely on using the full UUID for special cases, such as the
> board/sifive/hifive-unleashed/genimage_sdcard.cfg (PATCH 15/16).

There are tools that expect those values, to autodetect partitions. This
is the case, of course, of systemd-gpt-auto-generator, which will lookup
the partition UUIDs, but other tools may expect these UUIDs too.

I am not saying that we would cause trouble by changing our board
descriptions, but if we want to allow people to just copy them as the
base for their own development, then diverging from expected behaviour
is not nice.

> This way, it would be pretty clear that we have the "common cases" (boot
> partition, rootfs partition) and the "odd/special cases".

I think the "common case" would be "adhere to spec, use specified
values", while the exceptions are "the spec says nothing, use something
else and comment it".

Regards,
Yann E. MORIN.

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