refactor(squash): structure in a cleaner way

Simplify the squash mount layout. Instead of overlay on each top
directory (/etc, /usr), just mount and switch_root into the squash
image, with a overlay on top of it.

Also install the binaries and setup scripts separately, so the squash
setup code and the squash image content is independent of each other,
all squash setup script and binaries can be deleted safely upon
switch_root.

With this change, previous squash clean up service and other tricky
implementations are all gone.

This commit depends on systemd commits from:
systemd/systemd#18124

Previouly systemd doesn't recognize non-ramfs initramfs, now this is
doable with SYSTEMD_IN_INITRD=lenient

Signed-off-by: Kairui Song <kasong@redhat.com>

dracut-initramfs-restore.sh

@@ -48,9 +48,9 @@ else
 fi
 
 if [[ -d squash ]]; then
-    unsquashfs -no-xattrs -f -d . squash/root.img >/dev/null
+    unsquashfs -no-xattrs -f -d . squash-root.img >/dev/null
     if [ $? -ne 0 ]; then
-        echo "Squash module is enabled for this initramfs but failed to unpack squash/root.img" >&2
+        echo "Squash module is enabled for this initramfs but failed to unpack squash-root.img" >&2
         rm -f -- /run/initramfs/shutdown
         exit 1
     fi

dracut.sh

@@ -2057,8 +2057,8 @@ fi
 
 if dracut_module_included "squash"; then
     readonly squash_dir="$initdir/squash/root"
-    readonly squash_img="$initdir/squash/root.img"
-
+    readonly squash_img="$initdir/squash-root.img"
+    mkdir -p "$squash_dir"
     dinfo "*** Install squash loader ***"
     DRACUT_SQUASH_POST_INST=1 module_install "squash"
 fi

lsinitrd.sh

@@ -169,7 +169,7 @@ list_files()
 
 list_squash_content()
 {
-    SQUASH_IMG="squash/root.img"
+    SQUASH_IMG="squash-root.img"
     SQUASH_TMPFILE="$TMPDIR/initrd.root.sqsh"
 
     $CAT "$image" 2>/dev/null | cpio --extract --verbose --quiet --to-stdout -- \

modules.d/99squash/init-squash.sh

@@ -1,61 +1,29 @@
-#!/bin/bash
+#!/bin/sh
 PATH=/bin:/sbin
 
-SQUASH_IMG=/squash/root.img
-SQUASH_MNT=/squash/root
+# Basic mounts for mounting a squash image
+mkdir /proc /sys /dev /run
+mount -t proc -o nosuid,noexec,nodev proc /proc
+mount -t sysfs -o nosuid,noexec,nodev sysfs /sys
+mount -t devtmpfs -o mode=755,noexec,nosuid,strictatime devtmpfs /dev
+mount -t tmpfs -o mode=755,nodev,nosuid,strictatime tmpfs /run
 
-# Following mount points are neccessary for mounting a squash image
-
-[ ! -d /proc/self ] && \
-    mount -t proc -o nosuid,noexec,nodev proc /proc
-
-[ ! -d /sys/kernel ] && \
-    mount -t sysfs -o nosuid,noexec,nodev sysfs /sys
-
-[ ! -e /dev/loop-control ] && \
-    mount -t devtmpfs -o mode=0755,noexec,nosuid,strictatime devtmpfs /dev
-
-# Need a loop device backend, overlayfs, and squashfs module
+# Load required modules
 modprobe loop
-if [ $? != 0 ]; then
-    echo "Unable to setup loop module"
-fi
-
 modprobe squashfs
-if [ $? != 0 ]; then
-    echo "Unable to setup squashfs module"
-fi
-
 modprobe overlay
-if [ $? != 0 ]; then
-    echo "Unable to setup overlay module"
-fi
-
-[ ! -d "$SQUASH_MNT" ] && \
-	mkdir -m 0755 -p $SQUASH_MNT
-
-# Mount the squashfs image
-mount -t squashfs -o ro,loop $SQUASH_IMG $SQUASH_MNT
-
-if [ $? != 0 ]; then
-    echo "Unable to mount squashed initramfs image"
-fi
-
-for file in $SQUASH_MNT/*; do
-	file=${file#$SQUASH_MNT/}
-	lowerdir=$SQUASH_MNT/$file
-	workdir=/squash/overlay-work/$file
-	upperdir=/$file
-	mntdir=/$file
 
-	mkdir -m 0755 -p $workdir
-	mkdir -m 0755 -p $mntdir
+# Mount the squash image
+mount -t ramfs ramfs /squash
+mkdir -p /squash/root /squash/overlay/upper /squash/overlay/work
+mount -t squashfs -o ro,loop /squash-root.img /squash/root
 
-	mount -t overlay overlay -o\
-		lowerdir=$lowerdir,upperdir=$upperdir,workdir=$workdir $mntdir
-done
+# Setup new root overlay
+mkdir /newroot
+mount -t overlay overlay -o lowerdir=/squash/root,upperdir=/squash/overlay/upper,workdir=/squash/overlay/work/ /newroot/
 
-exec /init.orig
+# Move all mount points to new root to prepare chroot
+mount --move /squash /newroot/squash
 
-echo "Something went wrong when trying to exec original init!"
-exit 1
+# Jump to new root and clean setup files
+SYSTEMD_IN_INITRD=lenient exec switch_root /newroot /init

modules.d/99squash/module-setup.sh

@@ -19,56 +19,36 @@ depends() {
 }
 
 installpost() {
-    local squash_candidate=( "usr" "etc" )
-
-    # shellcheck disable=SC2174
-    mkdir -m 0755 -p "$squash_dir"
-    for folder in "${squash_candidate[@]}"; do
-        mv "$initdir/$folder" "$squash_dir/$folder"
+    # Move everything under $initdir except $squash_dir
+    # itself into squash image
+    for i in "$initdir"/*; do
+        [[ "$squash_dir" == "$i"/* ]] || mv "$i" "$squash_dir"/
     done
 
-    # Move some files out side of the squash image, including:
-    # - Files required to boot and mount the squashfs image
-    # - Files need to be accessible without mounting the squash image
-    # - Initramfs marker
-    for file in \
-        "$squash_dir"/usr/lib/dracut/* \
-        "$squash_dir"/etc/initrd-release
-    do
+    # Create mount points for squash loader
+    mkdir -p "$initdir"/squash/
+    mkdir -p "$squash_dir"/squash/
+
+    # Copy dracut spec files out side of the squash image
+    # so dracut rebuild and lsinitrd can work
+    for file in "$squash_dir"/usr/lib/dracut/*; do
         [[ -f $file ]] || continue
         DRACUT_RESOLVE_DEPS=1 dracutsysrootdir="$squash_dir" inst "${file#$squash_dir}"
-        rm "$file"
-    done
-
-    # Install required files for the squash image setup script.
-    inst_multiple modprobe mount mkdir ln echo rm
-
-    mv "$initdir"/init "$initdir"/init.orig
-    inst "$moddir"/init-squash.sh /init
-    inst "$moddir"/clear-squash.sh /squash/clear-squash.sh
-
-    # Keep systemctl outsite if we need switch root
-    if [[ ! -f "$initdir/lib/dracut/no-switch-root" ]]; then
-      inst "systemctl"
-    fi
-
-    # Remove duplicated files
-    for folder in "${squash_candidate[@]}"; do
-        find "$initdir/$folder/" -not -type d \
-            -exec bash -c 'mv -f "$squash_dir${1#$initdir}" "$1"' -- "{}" \;
     done
 
-    # Install required modules for the squash image init script.
+    # Install required modules and binaries for the squash image init script.
+    DRACUT_RESOLVE_DEPS=1 inst_multiple sh mount modprobe mkdir switch_root
     hostonly="" instmods "loop" "squashfs" "overlay"
     dracut_kernel_post
+
+    # Install squash image init script.
+    ln -sfn /usr/bin "$initdir/bin"
+    ln -sfn /usr/sbin "$initdir/sbin"
+    inst_simple "$moddir"/init-squash.sh /init
 }
 
 install() {
     if [[ $DRACUT_SQUASH_POST_INST ]]; then
         installpost
-        return
     fi
-
-    inst "$moddir/squash-mnt-clear.service" "$systemdsystemunitdir/squash-mnt-clear.service"
-    $SYSTEMCTL -q --root "$initdir" add-wants initrd-switch-root.target squash-mnt-clear.service
 }