feat(dracut-initramfs-restore.sh): get compression method from image

Instead of trying every possible compression method until the right one is
found, parse the header of the initramfs image to get the right one and use it
without hiding possible decompression errors, using the same logic that is
implemented in `lsinitrd.sh`.

dracut-initramfs-restore.sh

@@ -11,54 +11,61 @@ set -e
 # switching root to an incompletely unpacked initramfs
 trap 'echo "Received SIGTERM signal, ignoring!" >&2' TERM
 
-KERNEL_VERSION="$(uname -r)"
-
 [[ $dracutbasedir ]] || dracutbasedir=/usr/lib/dracut
-SKIP="$dracutbasedir/skipcpio"
-[[ -x $SKIP ]] || SKIP="cat"
-
-if [[ -d /efi/Default ]] || [[ -d /boot/Default ]] || [[ -d /boot/efi/Default ]]; then
-    MACHINE_ID="Default"
-elif [[ -s /etc/machine-id ]]; then
-    read -r MACHINE_ID < /etc/machine-id
-    [[ $MACHINE_ID == "uninitialized" ]] && MACHINE_ID="Default"
-else
-    MACHINE_ID="Default"
-fi
+
+# shellcheck source=./dracut-functions.sh
+. "$dracutbasedir"/dracut-functions.sh
 
 mount -o ro /boot &> /dev/null || true
 
-if [[ -d /efi/loader/entries || -L /efi/loader/entries ]] \
-    && [[ -d /efi/$MACHINE_ID || -L /efi/$MACHINE_ID ]]; then
-    IMG="/efi/${MACHINE_ID}/${KERNEL_VERSION}/initrd"
-elif [[ -d /boot/loader/entries || -L /boot/loader/entries ]] \
-    && [[ -d /boot/$MACHINE_ID || -L /boot/$MACHINE_ID ]]; then
-    IMG="/boot/${MACHINE_ID}/${KERNEL_VERSION}/initrd"
-elif [[ -d /boot/efi/loader/entries || -L /boot/efi/loader/entries ]] \
-    && [[ -d /boot/efi/$MACHINE_ID || -L /boot/efi/$MACHINE_ID ]]; then
-    IMG="/boot/efi/$MACHINE_ID/$KERNEL_VERSION/initrd"
-elif [[ -f /lib/modules/${KERNEL_VERSION}/initrd ]]; then
-    IMG="/lib/modules/${KERNEL_VERSION}/initrd"
-elif [[ -f /boot/initramfs-${KERNEL_VERSION}.img ]]; then
-    IMG="/boot/initramfs-${KERNEL_VERSION}.img"
-elif mountpoint -q /efi; then
-    IMG="/efi/$MACHINE_ID/$KERNEL_VERSION/initrd"
-elif mountpoint -q /boot/efi; then
-    IMG="/boot/efi/$MACHINE_ID/$KERNEL_VERSION/initrd"
+# shellcheck disable=SC2119
+IMG="$(get_default_initramfs_image)"
+if [[ -z $IMG ]]; then
+    echo "No initramfs image found to restore!" >&2
+    exit 1
+fi
+
+# check if initramfs image contains early microcode and skip it
+read -r -N 6 bin < "$IMG"
+case $bin in
+    $'\x71\xc7'* | 070701)
+        CAT="cat --"
+        if has_early_microcode "$IMG"; then
+            SKIP="$dracutbasedir/skipcpio"
+            if ! [[ -x $SKIP ]]; then
+                echo "'$SKIP' not found, cannot skip early microcode to extract $IMG" >&2
+                exit 1
+            fi
+        fi
+        ;;
+esac
+
+if [[ $SKIP ]]; then
+    bin="$($SKIP "$IMG" | { read -r -N 6 bin && echo "$bin"; })"
 else
-    echo "No initramfs image found to restore!"
+    read -r -N 6 bin < "$IMG"
+fi
+
+# check if initramfs image is compressed
+CAT=$(get_decompression_command "$bin")
+
+type "${CAT%% *}" > /dev/null 2>&1 || {
+    echo "'${CAT%% *}' not found, cannot unpack $IMG" >&2
     exit 1
+}
+
+skipcpio() {
+    $SKIP "$@" | $ORIG_CAT
+}
+
+if [[ $SKIP ]]; then
+    ORIG_CAT="$CAT"
+    CAT=skipcpio
 fi
 
+# decompress and extract initramfs image
 cd /run/initramfs
-
-if (command -v zcat > /dev/null && $SKIP "$IMG" 2> /dev/null | zcat 2> /dev/null | cpio -id --no-absolute-filenames --quiet > /dev/null 2>&1) \
-    || (command -v bzcat > /dev/null && $SKIP "$IMG" 2> /dev/null | bzcat 2> /dev/null | cpio -id --no-absolute-filenames --quiet > /dev/null 2>&1) \
-    || (command -v xzcat > /dev/null && $SKIP "$IMG" 2> /dev/null | xzcat 2> /dev/null | cpio -id --no-absolute-filenames --quiet > /dev/null 2>&1) \
-    || (command -v lz4 > /dev/null && $SKIP "$IMG" 2> /dev/null | lz4 -d -c 2> /dev/null | cpio -id --no-absolute-filenames --quiet > /dev/null 2>&1) \
-    || (command -v lzop > /dev/null && $SKIP "$IMG" 2> /dev/null | lzop -d -c 2> /dev/null | cpio -id --no-absolute-filenames --quiet > /dev/null 2>&1) \
-    || (command -v zstd > /dev/null && $SKIP "$IMG" 2> /dev/null | zstd -d -c 2> /dev/null | cpio -id --no-absolute-filenames --quiet > /dev/null 2>&1) \
-    || ($SKIP "$IMG" 2> /dev/null | cpio -id --no-absolute-filenames --quiet > /dev/null 2>&1); then
+if ($CAT "$IMG" | cpio -id --no-absolute-filenames --quiet > /dev/null); then
     rm -f -- .need_shutdown
 else
     # something failed, so we clean up