Re: [PATCH v2] scripts/make-gpt.sh: allow setting partition size

[Alyssa Ross <hi@alyssa.is>]

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Demi Marie Obenour <demiobenour@gmail.com> writes:

> On 11/28/25 16:14, Alyssa Ross wrote:
>> Demi Marie Obenour <demiobenour@gmail.com> writes:
>> 
>>> On 11/28/25 08:22, Alyssa Ross wrote:
>>>> We want non-minimally-sized partitions to leave space for updates.
>>>> All such partitions will also be labelled, so we can just add another
>>>> optional field at the end.
>>>>
>>>> Since we don't parse partition specifications in sh, we can't keep a
>>>> running total any more, so instead we just go through the table at the
>>>> end and add up all the sizes, taking advantage of our knowledge that
>>>> the size will always be the last thing in each line in our tables.
>>>>
>>>> Signed-off-by: Alyssa Ross <hi@alyssa.is>
>>>> Message-ID: <20251127174054.2056835-2-hi@alyssa.is>
>>>> ---
>>>> v2: fix conflicts after applying Demi's optimization, and avoid awk
>>>>     to sum partition sizes, taking inspiration from the same.
>>>> v1: https://spectrum-os.org/lists/archives/spectrum-devel/20251127174054.2056835-2-hi@alyssa.is/
>>>>
>>>>  scripts/make-gpt.sh      | 30 ++++++++++++++++++------------
>>>>  scripts/sfdisk-field.awk | 22 +++++++++++++++++-----
>>>>  2 files changed, 35 insertions(+), 17 deletions(-)
>>>>
>>>> diff --git a/scripts/make-gpt.sh b/scripts/make-gpt.sh
>>>> index 3cae441..cb19868 100755
>>>> --- a/scripts/make-gpt.sh
>>>> +++ b/scripts/make-gpt.sh
>>>> @@ -1,10 +1,10 @@
>>>>  #!/bin/sh -eu
>>>>  #
>>>> -# SPDX-FileCopyrightText: 2021-2023 Alyssa Ross <hi@alyssa.is>
>>>> +# SPDX-FileCopyrightText: 2021-2023, 2025 Alyssa Ross <hi@alyssa.is>
>>>>  # SPDX-FileCopyrightText: 2022 Unikie
>>>>  # SPDX-License-Identifier: EUPL-1.2+
>>>>  #
>>>> -# usage: make-gpt.sh GPT_PATH PATH:PARTTYPE[:PARTUUID[:PARTLABEL]]...
>>>> +# usage: make-gpt.sh GPT_PATH PATH:PARTTYPE[:PARTUUID[:PARTLABEL[:PARTMiB]]]...
>>>>  
>>>>  ONE_MiB=1048576
>>>>  
>>>> @@ -33,21 +33,27 @@ scriptsDir="$(dirname "$0")"
>>>>  out="$1"
>>>>  shift
>>>>  
>>>> -nl='
>>>> -'
>>>> -table="label: gpt"
>>>> +table=$(for partition; do
>>>> +	awk -f "$scriptsDir/sfdisk-field.awk" \
>>>> +		-v partition="$partition" \
>>>> +		-v size="$(sizeMiB "${partition%%:*}")"
>>>> +done)
>>>
>>> $(sizeMiB) should be moved into a separate command.  Shellcheck can
>>> catch this if you enable SC2312.
>> 
>> Good catch, thanks.  Feel free to suggest other optional shellcheck
>> things we should enable.  (Although I've just noticed
>> release/checks/shellcheck.nix doesn't seem to be reading the
>> .shellcheckrc file properly so don't use that for testing.)
>
> I'll look later.
>
>>>>  # Keep 1MiB free at the start, and 1MiB free at the end.
>>>> -gptBytes=$((ONE_MiB * 2))
>>>> -for partition; do
>>>> -	sizeMiB="$(sizeMiB "${partition%%:*}")"
>>>> -	table="$table${nl}size=${sizeMiB}MiB,$(awk -f "$scriptsDir/sfdisk-field.awk" -v partition="$partition")"
>>>> -	gptBytes="$((gptBytes + sizeMiB * ONE_MiB))"
>>>> -done
>>>> +gptMiB=2
>>>> +while read -r partition; do
>>>> +	# Here we rely on sfdisk-field.awk always putting size last.
>>>> +	: $((gptMiB += ${partition##*=}))
>>>> +done <<EOF
>>>> +$table
>>>> +EOF
>>>
>>> Nit: should ${partition##*=} be in double quotes?
>> 
>> I tried changing it, but it is apparently an "arithmetic syntax error"
>> to use double quotes here.
>
> I'd use a separate variable then.

Doesn't seem to make a difference.  As an experiment:

partition="size=2 + 3"
size=${partition##*=}
printf "%s\n" $(($size))

This prints 5 even though a separate variable is used.  It doesn't seem
to be possible to get $(( … )) *not* to interpret arithmetic in
variables.

In bash, but not busybox ash as used in Nix builds, it is possible to
use double quotes like you suggested, but $(("$size")) is /still/ 5.

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