scripts: Kernel bumper script

For years, we have struggled and been frustrated at loosing history of
files in git, due to the 'copy + add' strategy. This could have been
prevented with a double-commit 'mv + add' trick.

On the mailing list [0] the discussion was started to put the
instructions in a wiki. Instead, it is much better to just script it and
put it in the repo.

Instead of doing mv + copy, which leads to two commits, but no history
on the copied files, it uses move, + copy and merge, which results in
three (merge) commits, but keeps the history of all files. As always
with renames, `--follow` will be needed.

The tool is trivial and works either in the OpenWrt git root directory,
or in the actual target directory.

Tested on the `realtek` and generic targets.

Note, that the tool does not do any of the labor needed after the move,
such as updating configs, dropping patches etc.

To make sure this script is easily found by any developer, who just
wants to do a kernel bump, the script is added here and not to
maintainer-tools repo as those scripts are a little bit more specialized.
Bumping a kernel is a trivial task that often regular developers do,
where most do not even know the existence of maintainer tools, are not
part of the main repo they'd clone, not part of the docker container
they'd use and so discoverability is probably much more important.

[0]: https://lists.openwrt.org/pipermail/openwrt-devel/2023-October/041673.html

Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
Tested-by: Robert Marko <robimarko@gmail.com>
Tested-by: Weijie Gao <hackpascal@gmail.com>

scripts/kernel_bump.sh

@@ -0,0 +1,225 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
+# Copyright (C) 2024 Olliver Schinagl <oliver@schinagl.nl>
+
+set -eu
+if [ -n "${DEBUG_TRACE_SH:-}" ] && \
+   [ "${DEBUG_TRACE_SH:-}" != "${DEBUG_TRACE_SH#*"$(basename "${0}")"*}" ] || \
+   [ "${DEBUG_TRACE_SH:-}" = 'all' ]; then
+	set -x
+fi
+
+REQUIRED_COMMANDS='
+	[
+	basename
+	command
+	echo
+	exit
+	git
+	printf
+	set
+	shift
+'
+
+_msg()
+{
+	_level="${1:?Missing argument to function}"
+	shift
+
+	if [ "${#}" -le 0 ]; then
+		echo "${_level}: No content for this message ..."
+		return
+	fi
+
+	echo "${_level}: ${*}"
+}
+
+e_err()
+{
+	_msg 'err' "${*}" >&2
+}
+
+e_warn()
+{
+	_msg 'warning' "${*}"
+}
+
+e_notice()
+{
+	_msg 'notice' "${*}"
+}
+
+usage()
+{
+	echo "Usage: ${0}"
+	echo 'Helper script to bump the target kernel version, whilst keeping history.'
+	echo "    -p  Optional Platform name (e.g. 'ath79' [PLATFORM_NAME]"
+	echo "    -s  Source version of kernel (e.g. 'v6.1' [SOURCE_VERSION])"
+	echo "    -t  Target version of kernel (e.g. 'v6.6' [TARGET_VERSION]')"
+	echo
+	echo 'All options can also be passed in environment variables (listed between [BRACKETS]).'
+	echo 'Example: scripts/kernel_bump.sh -p realtek -s v6.1 -t v6.6'
+}
+
+cleanup()
+{
+	trap - EXIT HUP INT QUIT ABRT ALRM TERM
+
+	if [ -n "${initial_branch:-}" ] && \
+	   [ "$(git rev-parse --abbrev-ref HEAD)" != "${initial_branch:-}" ]; then
+		git switch "${initial_branch}"
+	fi
+}
+
+init()
+{
+	initial_branch="$(git rev-parse --abbrev-ref HEAD)"
+	initial_commitish="$(git rev-parse HEAD)"
+
+	trap cleanup EXIT HUP INT QUIT ABRT ALRM TERM
+}
+
+do_source_target()
+{
+	_target_dir="${1:?Missing argument to function}"
+	_op="${2:?Missing argument to function}"
+
+}
+
+bump_kernel()
+{
+	platform_name="${platform_name##*'/'}"
+
+	if [ -z "${platform_name:-}" ]; then
+		platform_name="${PWD##*'/'}"
+	fi
+
+	if [ "${PWD##*'/'}" = "${platform_name}" ]; then
+		_target_dir='./'
+	else
+		_target_dir="target/linux/${platform_name}"
+	fi
+
+	if [ ! -d "${_target_dir}/image" ]; then
+		e_err 'Cannot find target linux directory.'
+		exit 1
+	fi
+
+	git switch --force-create '__openwrt_kernel_files_mover'
+
+	for _path in "${_target_dir}/"*; do
+		if [ ! -s "${_path}" ] || \
+		   [ "${_path}" = "${_path%%"-${source_version}"}" ]; then
+			continue
+		fi
+
+		_target_path="${_path%%"-${source_version}"}-${target_version}"
+		if [ -s "${_target_path}" ]; then
+			e_err "Target '${_target_path}' already exists!"
+			exit 1
+		fi
+
+		git mv \
+			"${_path}" \
+			"${_target_path}"
+	done
+
+	find "${_target_dir}" -iname "config-${source_version}" | while read -r _config; do
+		_path="${_config%%"/config-${source_version}"}"
+		git mv "${_config}" "${_path}/config-${target_version}"
+	done
+
+	git commit \
+		--signoff \
+		--message "kernel/${platform_name}: Create kernel files for v${target_version} (from v${source_version})" \
+		--message 'This is an automatically generated commit.' \
+		--message 'During a `git bisect` session, `git bisect --skip` is recommended.'
+
+	git checkout 'HEAD~' "${_target_dir}"
+	git commit \
+		--signoff \
+		--message "kernel/${platform_name}: Restore kernel files for v${source_version}" \
+		--message "$(printf "This is an automatically generated commit which aids following Kernel patch history,\nas git will see the move and copy as a rename thus defeating the purpose.\n\nSee: https://lists.openwrt.org/pipermail/openwrt-devel/2023-October/041673.html\nfor the original discussion.")"
+	git switch "${initial_branch:?Unable to switch back to original branch. Quitting.}"
+	GIT_EDITOR=true git merge --no-ff '__openwrt_kernel_files_mover'
+	git branch --delete '__openwrt_kernel_files_mover'
+
+	echo "Original commitish was '${initial_commitish}'."
+	echo 'Kernel bump complete. Remember to use `git log --follow`.'
+}
+
+check_requirements()
+{
+	for _cmd in ${REQUIRED_COMMANDS}; do
+		if ! _test_result="$(command -V "${_cmd}")"; then
+			_test_result_fail="${_test_result_fail:-}${_test_result}\n"
+		else
+			_test_result_pass="${_test_result_pass:-}${_test_result}\n"
+		fi
+	done
+
+	echo 'Available commands:'
+	# As the results contain \n, we expect these to be interpreted.
+	# shellcheck disable=SC2059
+	printf "${_test_result_pass:-none\n}"
+	echo
+	echo 'Missing commands:'
+	# shellcheck disable=SC2059
+	printf "${_test_result_fail:-none\n}"
+	echo
+
+	if [ -n "${_test_result_fail:-}" ]; then
+		echo 'Command test failed, missing programs.'
+		test_failed=1
+	fi
+}
+
+main()
+{
+	while getopts 'hp:s:t:' _options; do
+		case "${_options}" in
+		'h')
+			usage
+			exit 0
+			;;
+		'p')
+			platform_name="${OPTARG}"
+			;;
+		's')
+			source_version="${OPTARG#v}"
+			;;
+		't')
+			target_version="${OPTARG#v}"
+			;;
+		':')
+			e_err "Option -${OPTARG} requires an argument."
+			exit 1
+			;;
+		*)
+			e_err "Invalid option: -${OPTARG}"
+			exit 1
+			;;
+		esac
+	done
+	shift "$((OPTIND - 1))"
+
+	platform_name="${platform_name:-${PLATFORM_NAME:-}}"
+	source_version="${source_version:-${SOURCE_VERSION:-}}"
+	target_version="${target_version:-${TARGET_VERSION:-}}"
+
+	if [ -z "${source_version:-}" ] || [ -z "${target_version:-}" ]; then
+		e_err "Source (${source_version}) and target (${target_version}) versions need to be defined."
+		exit 1
+	fi
+
+	check_requirements
+
+	init
+	bump_kernel
+	cleanup
+}
+
+main "${@}"
+
+exit 0