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e6047ee5e8
Renaming the 'rootrw' kernel commandline parameter to 'overlayrootrwdev' to both align better with this modules name, and point out the usage of the variable. This patch also includes an if block to migrate the old 'rootrw' block, should it be already used by someone. (From OE-Core rev: a52b7f5c8ff3e50707b55843d9996983ab8efae2) Signed-off-by: Johannes Schneider <johannes.schneider@leica-geosystems.com> Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
119 lines
4.0 KiB
Bash
119 lines
4.0 KiB
Bash
#!/bin/sh
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# SPDX-License-Identifier: MIT
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#
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# Copyright 2022 (C), Microsoft Corporation
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# Simple initramfs module intended to mount a read-write (RW)
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# overlayfs on top of /, keeping the original root filesystem
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# as read-only (RO), free from modifications by the user.
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#
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# NOTE: The read-only IMAGE_FEATURE is not required for this to work
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#
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# This script is based on the overlay-etc.bbclass, which sets up
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# an overlay on top of the /etc directory, but in this case allows
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# accessing the original, unmodified rootfs at /rofs after boot.
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#
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# It relies on the initramfs-module-rootfs to mount the original
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# root filesystem, and requires 'overlayrootrwdev=<foo>' to be passed as a
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# kernel parameter, specifying the device/partition intended to
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# use as RW.
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# Mount options of the RW device can be tweaked with 'overlayrootfstype='
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# (defaults to 'ext4') and 'overlayrootfsflags=' ('defaults').
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#
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# This module needs to be executed after the initramfs-module-rootfs
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# since it relies on it to mount the filesystem at initramfs startup
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# but before the finish module which normally switches root.
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# After overlayroot is executed the usual boot flow continues from
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# the real init process.
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#
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# If something goes wrong while running this module, the rootfs
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# is still mounted RO (with no overlay) and the finish module is
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# executed to continue booting normally.
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#
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# It also has a dependency on overlayfs being enabled in the
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# running kernel via KERNEL_FEATURES (kmeta) or any other means.
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PATH=/sbin:/bin:/usr/sbin:/usr/bin
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# We get OLDROOT from the rootfs module
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OLDROOT="/rootfs"
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NEWROOT="${RWMOUNT}/root"
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RWMOUNT="/overlay"
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ROMOUNT="${RWMOUNT}/rofs"
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UPPER_DIR="${RWMOUNT}/upper"
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WORK_DIR="${RWMOUNT}/work"
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MODULES_DIR=/init.d
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# Something went wrong, make sure / is mounted as read only anyway.
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exit_gracefully() {
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echo $1 >/dev/console
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echo >/dev/console
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echo "OverlayRoot mounting failed, starting system as read-only" >/dev/console
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echo >/dev/console
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# The following is borrowed from rootfs-postcommands.bbclass
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# This basically looks at the real rootfs mounting options and
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# replaces them with "ro"
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# Tweak the mount option and fs_passno for rootfs in fstab
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if [ -f ${OLDROOT}/etc/fstab ]; then
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sed -i -e '/^[#[:space:]]*\/dev\/root/{s/defaults/ro/;s/\([[:space:]]*[[:digit:]]\)\([[:space:]]*\)[[:digit:]]$/\1\20/}' ${OLDROOT}/etc/fstab
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fi
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# Tweak the "mount -o remount,rw /" command in busybox-inittab inittab
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if [ -f ${OLDROOT}/etc/inittab ]; then
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sed -i 's|/bin/mount -o remount,rw /|/bin/mount -o remount,ro /|' ${OLDROOT}/etc/inittab
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fi
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# Continue as if the overlayroot module didn't exist to continue booting
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. $MODULES_DIR/99-finish
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eval "finish_run"
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}
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# migrate legacy parameter
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if [ ! -z "$bootparam_rootrw" ]; then
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bootparam_overlayrootrwdev="$bootparam_rootrw"
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fi
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if [ -z "$bootparam_overlayrootrwdev" ]; then
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exit_gracefully "overlayrootrwdev= kernel parameter doesn't exist and its required to mount the overlayfs"
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fi
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mkdir -p ${RWMOUNT}
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# Mount RW device
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if mount -n -t ${bootparam_overlayrootfstype:-ext4} -o ${bootparam_overlayrootfsflags:-defaults} ${bootparam_overlayrootrwdev} ${RWMOUNT}
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then
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# Set up overlay directories
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mkdir -p ${UPPER_DIR}
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mkdir -p ${WORK_DIR}
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mkdir -p ${NEWROOT}
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mkdir -p ${ROMOUNT}
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# Remount OLDROOT as read-only
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mount -o bind ${OLDROOT} ${ROMOUNT}
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mount -o remount,ro ${ROMOUNT}
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# Mount RW overlay
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mount -t overlay overlay -o lowerdir=${ROMOUNT},upperdir=${UPPER_DIR},workdir=${WORK_DIR} ${NEWROOT} || exit_gracefully "initramfs-overlayroot: Mounting overlay failed"
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else
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exit_gracefully "initramfs-overlayroot: Mounting RW device failed"
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fi
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# Set up filesystems on overlay
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mkdir -p ${NEWROOT}/proc
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mkdir -p ${NEWROOT}/dev
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mkdir -p ${NEWROOT}/sys
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mkdir -p ${NEWROOT}/rofs
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mount -n --move ${ROMOUNT} ${NEWROOT}/rofs
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mount -n --move /proc ${NEWROOT}/proc
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mount -n --move /sys ${NEWROOT}/sys
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mount -n --move /dev ${NEWROOT}/dev
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exec chroot ${NEWROOT}/ ${bootparam_init:-/sbin/init} || exit_gracefully "Couldn't chroot into overlay"
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