bindings: python: add a script to generate 32-bit ARM (armv7l) wheels

Add a 'generate_armv7l_wheels.sh' shell script that makes armv7l (32-bit
ARM) Python wheels for combinations of libc (glibc, musl) and selected
CPython versions.

Currently, Python wheels are generated for the x86_64 and aarch64 CPU
architectures only, using the 'cibuildwheel' tool invoked by the existing
'generate_pypi_artifacts.sh' script. The 'cibuildwheel' tool, in turn,
relies on the PyPA manylinux and musllinux Docker images that, sadly, are
not available for 32-bit ARM architectures that are relatively common in
edge devices.

It was previously suggested that Python users could rely on the
piwheels.org repository for 32-bit ARM gpiod wheels. Alas, that repository
lags seriously behind the latest CPython releases. It currently provides
gpiod wheels for CPython versions 3.9 and 3.11 only, while CPython 3.12
was released 11 months ago and CPython 3.13 will be released in about 1
month's time.

It turns out that armv7l Python wheels can be relatively easily generated
without 'cibuildwheel', in about 150 lines of structured shell script
that introduce no new requirements (the script depends on Docker and
binfmt_misc only). Instead of manylinux and musllinux Docker images, the
script uses the official Python image in Docker Hub, which is available
for armv7l in Debian and Alpine flavours (for glibc and musl libc
respectively). This commit introduces such a shell script.

Signed-off-by: Paulo Ferreira de Castro <[email protected]>

bindings/python/generate_armv7l_wheels.sh

@@ -0,0 +1,153 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: GPL-2.0-or-later
+# SPDX-FileCopyrightText: 2024 Paulo Ferreira de Castro <[email protected]>
+#
+# This script makes armv7l gpiod Python wheels for combinations of libc (glibc
+# and musl) and CPython versions, complementing the wheels made by cibuildwheel
+# (through the 'generate_pypi_artifacts.sh' script).
+#
+# Modify the TARGET_PYTHON_VERSIONS global variable below in order to change
+# the targeted CPython versions.
+#
+# Dependencies: Docker and binfmt_misc for ARM emulation.
+#
+# Usage:
+# ./generate_armv7l_wheels.sh
+#
+# The wheels will be placed in the ./dist directory.
+#
+
+TARGET_PYTHON_VERSIONS=(3.9 3.10 3.11 3.12)
+CPU_ARCH='armv7l'
+DOCKER_PLATFORM='linux/arm/v7'
+ALPINE_DEPENDENCIES="
+	RUN apk add autoconf autoconf-archive automake bash binutils curl \
+		g++ git libtool linux-headers make patchelf pkgconfig
+"
+DEBIAN_DEPENDENCIES="
+	RUN apt-get update && apt-get install -y autoconf-archive
+	# auditwheel requires patchelf v0.14+, but Debian Bullseye comes with v0.12.
+	RUN curl -Ls 'https://github.com/NixOS/patchelf/releases/download/0.18.0/patchelf-0.18.0-${CPU_ARCH}.tar.gz' \
+		| tar -xzC /usr ./bin/patchelf
+"
+# Docker image used to run Python commands locally (host CPU architecture).
+NATIVE_PYTHON_IMG="python:3.12-alpine"
+
+quit() {
+	echo -e "\n${1}"
+	exit 1
+}
+
+print_gpiod_version() {
+	# Print the gpiod Python binding version from gpiod/version.py.
+	set -x
+	docker run --rm -iv "${PWD}/gpiod:/gpiod" "${NATIVE_PYTHON_IMG}" python <<-EOF
+		import sys
+		sys.path.insert(0, "/gpiod")
+		from version import __version__
+		print(__version__)
+	EOF
+	{ local status="$?"; set +x; } 2>/dev/null
+	return "${status}"
+}
+
+ensure_sdist() {
+	# Make the sdist if it does not already exist in the './dist' directory.
+	local gpiod_version
+	gpiod_version="$(print_gpiod_version)" || \
+		quit "Failed to determine the gpiod Python binding version"
+
+	SDIST_TARBALL="gpiod-${gpiod_version}.tar.gz"
+	if [ -f "dist/${SDIST_TARBALL}" ]; then
+		return
+	fi
+	if [ -z "${LIBGPIOD_VERSION}" ]; then
+		quit "Please set the LIBGPIOD_VERSION env var to enable making the sdist."
+	fi
+	set -x
+	docker run --rm -v "${PWD}:/py_bindings" -w /py_bindings -e LIBGPIOD_VERSION \
+		"${NATIVE_PYTHON_IMG}" python setup.py sdist
+	{ local status="$?"; set +x; } 2>/dev/null
+	return "${status}"
+}
+
+make_wheel_builder_image() {
+	# Make a "wheel builder" docker image used to build gpiod wheels.
+	# The base image is the official Python image on Docker Hub, in either the
+	# Debian variant (glibc) or the Alpine variant (musl). Currently using
+	# Debian 11 Bullseye because it supports building wheels targeting glibc
+	# v2.17. The newer Debian 12 Bookworm supports higher glibc versions only.
+
+	local libc="$1" # The string 'glibc' or 'musl'
+	local builder_img_tag="$2"
+	local python_version="$3"
+	local distro=
+	local distro_deps=
+	case "${libc}" in
+		glibc) distro="bullseye"; distro_deps="${DEBIAN_DEPENDENCIES}";;
+		musl) distro="alpine3.20"; distro_deps="${ALPINE_DEPENDENCIES}";;
+	esac
+	set -x
+	docker build --platform "${DOCKER_PLATFORM}" --pull --progress plain \
+		--tag "${builder_img_tag}" --file - . <<-EOF
+			FROM 'python:${python_version}-${distro}'
+			${distro_deps}
+			RUN pip install auditwheel
+		EOF
+	{ local status="$?"; set +x; } 2>/dev/null
+	return "${status}"
+}
+
+build_wheel() {
+	# Build a gpiod wheel in a container of the given builder image tag.
+	local libc="$1" # The string 'glibc' or 'musl'
+	local builder_img_tag="$2"
+	local libc_plat=
+	case "${libc}" in
+		glibc) libc_plat="manylinux_2_17_${CPU_ARCH}";;
+		musl) libc_plat="musllinux_1_2_${CPU_ARCH}";;
+	esac
+	set -x
+	docker run --rm --platform "${DOCKER_PLATFORM}" -iv "${PWD}/dist:/dist" \
+		-w /tmp "${builder_img_tag}" bash <<-EOF
+			set -ex
+			pip wheel --no-deps "/dist/${SDIST_TARBALL}"
+			auditwheel repair --plat "${libc_plat}" --wheel-dir /dist ./*.whl
+		EOF
+	{ local status="$?"; set +x; } 2>/dev/null
+	return "${status}"
+}
+
+build_combinations() {
+	# Build gpiod wheels for combinations of libc and Python versions.
+	local builder_img_tag
+	for libc in glibc musl; do
+		for ver in "${TARGET_PYTHON_VERSIONS[@]}"; do
+			builder_img_tag="gpiod-wheel-builder-cp${ver/./}-${libc}-${CPU_ARCH}"
+
+			make_wheel_builder_image "${libc}" "${builder_img_tag}" "${ver}" || \
+				quit "Failed to build Docker image '${builder_img_tag}'"
+
+			build_wheel "${libc}" "${builder_img_tag}" || \
+				quit "Failed to build gpiod wheel with image '${builder_img_tag}'"
+
+			set -x
+			docker image rm "${builder_img_tag}"
+			{ set +x; } 2>/dev/null
+		done
+	done
+}
+
+main() {
+	set -e
+	local script_dir # Directory where this script is located
+	script_dir="$(cd -- "$(dirname "$0")" >/dev/null 2>&1 || true; pwd -P)"
+	cd "${script_dir}" || quit "'cd ${script_dir}' failed"
+	ensure_sdist || quit "Failed to find or make the sdist tarball."
+	build_combinations
+	echo
+	ls -l dist/*"${CPU_ARCH}"*
+	echo -e "\nAll done! Hint: Use 'docker system prune' to free disk space."
+}
+
+main