Re: [PATCH] target-bootstrapper-service: add runtime serial tty drop-in generation

[Zhihang Wei <wzh@ilbers.de>]

Applied to next, thanks.

Zhihang

On 6/19/26 12:39, 'Gourav Singh' via isar-users wrote:
> Extend the recipe to support dynamically detected serial consoles without
> taking over every getty instance.
>
> The existing loop still installs overrides for statically configured
> TARGET_BOOTSTRAPPER_TTY_SERVICES. In addition, a runtime oneshot service
> and helper script are installed to detect the first available serial tty
> (ttyACM*/ttyUSB*/ttyAMA*/ttyGS*) and create one matching
> serial-getty@<tty>.service.d override from a stored template.
>
> This keeps installer behavior on configured ttys, adds support for
> runtime-discovered serial devices, and preserves other consoles for
> normal login/debug access.
>
> Signed-off-by: Gourav Singh <gouravsingh@siemens.com>
> ---
>   .../generate-target-bootstrapper-dropin.sh    | 47 +++++++++++++++++++
>   .../files/postinst.tmpl                       |  3 ++
>   ...arget-bootstrapper-generate-dropin.service | 12 +++++
>   .../target-bootstrapper-service.bb            | 14 +++++-
>   4 files changed, 74 insertions(+), 2 deletions(-)
>   create mode 100644 meta-isar/recipes-installer/target-bootstrapper-service/files/generate-target-bootstrapper-dropin.sh
>   create mode 100644 meta-isar/recipes-installer/target-bootstrapper-service/files/target-bootstrapper-generate-dropin.service
>
> diff --git a/meta-isar/recipes-installer/target-bootstrapper-service/files/generate-target-bootstrapper-dropin.sh b/meta-isar/recipes-installer/target-bootstrapper-service/files/generate-target-bootstrapper-dropin.sh
> new file mode 100644
> index 00000000..50c3ba40
> --- /dev/null
> +++ b/meta-isar/recipes-installer/target-bootstrapper-service/files/generate-target-bootstrapper-dropin.sh
> @@ -0,0 +1,47 @@
> +#!/bin/sh
> +# This software is a part of Isar.
> +# Copyright (C) Siemens AG, 2026
> +#
> +# SPDX-License-Identifier: MIT
> +
> +set -e
> +
> +OVERRIDE_DIR="/usr/lib/systemd/system"
> +DROP_IN_SUFFIX="d/10-target-bootstrapper.override.conf"
> +
> +# Check if override template exists
> +if [ ! -f "/usr/lib/target-bootstrapper.override.conf" ]; then
> +    exit 0
> +fi
> +
> +# Detect first available serial device (ttyACM*, ttyUSB*, ttyAMA*, etc.)
> +detect_first_serial_device() {
> +    for pattern in ttyACM ttyUSB ttyAMA ttyGS; do
> +        for dev in /dev/${pattern}*; do
> +            if [ -c "$dev" ]; then
> +                basename "$dev"
> +                return 0
> +            fi
> +        done
> +    done
> +}
> +
> +DETECTED_TTY=$(detect_first_serial_device 2>/dev/null)
> +
> +if [ -z "$DETECTED_TTY" ]; then
> +    exit 0
> +fi
> +
> +# Map device name to getty service instance
> +# e.g. ttyACM0 -> serial-getty@ttyACM0.service
> +TTY_SERVICE="serial-getty@${DETECTED_TTY}.service"
> +DROP_IN_DIR="${OVERRIDE_DIR}/${TTY_SERVICE}.d"
> +
> +# Create drop-in directory and install override
> +mkdir -p "$DROP_IN_DIR"
> +cp "/usr/lib/target-bootstrapper.override.conf" "$DROP_IN_DIR/${DROP_IN_SUFFIX##*/}"
> +
> +# Reload systemd to pick up new drop-ins
> +systemctl daemon-reload || true
> +
> +exit 0
> diff --git a/meta-isar/recipes-installer/target-bootstrapper-service/files/postinst.tmpl b/meta-isar/recipes-installer/target-bootstrapper-service/files/postinst.tmpl
> index 7c24af17..57851956 100644
> --- a/meta-isar/recipes-installer/target-bootstrapper-service/files/postinst.tmpl
> +++ b/meta-isar/recipes-installer/target-bootstrapper-service/files/postinst.tmpl
> @@ -5,3 +5,6 @@ set -e
>   for tty_service in ${TARGET_BOOTSTRAPPER_TTY_SERVICES}; do
>       deb-systemd-helper enable ${tty_service} || true
>   done
> +
> +# Enable the runtime detection service
> +deb-systemd-helper enable target-bootstrapper-generate-dropin.service || true
> diff --git a/meta-isar/recipes-installer/target-bootstrapper-service/files/target-bootstrapper-generate-dropin.service b/meta-isar/recipes-installer/target-bootstrapper-service/files/target-bootstrapper-generate-dropin.service
> new file mode 100644
> index 00000000..38457c8d
> --- /dev/null
> +++ b/meta-isar/recipes-installer/target-bootstrapper-service/files/target-bootstrapper-generate-dropin.service
> @@ -0,0 +1,12 @@
> +[Unit]
> +Description=Generate target-bootstrapper drop-in for detected serial devices
> +Before=serial-getty@.service getty@.service
> +After=dev-*.device
> +
> +[Service]
> +Type=oneshot
> +ExecStart=/usr/libexec/target-bootstrapper-service/generate-target-bootstrapper-dropin.sh
> +RemainAfterExit=yes
> +
> +[Install]
> +WantedBy=multi-user.target
> diff --git a/meta-isar/recipes-installer/target-bootstrapper-service/target-bootstrapper-service.bb b/meta-isar/recipes-installer/target-bootstrapper-service/target-bootstrapper-service.bb
> index e7a8b2a1..572cddcd 100644
> --- a/meta-isar/recipes-installer/target-bootstrapper-service/target-bootstrapper-service.bb
> +++ b/meta-isar/recipes-installer/target-bootstrapper-service/target-bootstrapper-service.bb
> @@ -25,6 +25,8 @@ inherit dpkg-raw
>   SRC_URI = "\
>       file://postinst.tmpl \
>       file://target-bootstrapper.override.conf \
> +    file://generate-target-bootstrapper-dropin.sh \
> +    file://target-bootstrapper-generate-dropin.service \
>       "
>   
>   TEMPLATE_FILES = "postinst.tmpl"
> @@ -33,11 +35,19 @@ TEMPLATE_VARS = "TARGET_BOOTSTRAPPER_TTY_SERVICES"
>   DEPENDS += " target-bootstrapper"
>   DEBIAN_DEPENDS = "target-bootstrapper"
>   
> -do_install[cleandirs] = "${D}/usr/lib/systemd/system/"
> +do_install[cleandirs] = "${D}/usr/lib/systemd/system/ ${D}/usr/libexec"
>   do_install() {
>       for svc_name in ${TARGET_BOOTSTRAPPER_TTY_SERVICES}
>       do
> -        mkdir -p ${D}/usr/lib/systemd/system/${svc_name}.service.d/
> +        install -d -m 0755 ${D}/usr/lib/systemd/system/${svc_name}.service.d/
>           install -m 0644 ${WORKDIR}/target-bootstrapper.override.conf ${D}/usr/lib/systemd/system/${svc_name}.service.d/10-target-bootstrapper.override.conf
>       done
> +
> +    # Install script and service for runtime detection of serial devices
> +    install -d -m 0755 ${D}/usr/libexec/${PN}/
> +    install -m 0755 ${WORKDIR}/generate-target-bootstrapper-dropin.sh ${D}/usr/libexec/${PN}/
> +    install -m 0644 ${WORKDIR}/target-bootstrapper-generate-dropin.service ${D}/usr/lib/systemd/system/
> +
> +    # Install override template for runtime use by the detection script
> +    install -m 0644 ${WORKDIR}/target-bootstrapper.override.conf ${D}/usr/lib/target-bootstrapper.override.conf
>   }

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