[dnbd3-rootfs] Add option to specify partition by number, add fallback

Fallback is to scan all partitions on the r/o device, or the r/o device
itself, for an init binary.

1 files changed, 57 insertions, 19 deletions

diff --git a/modules.d/dnbd3-rootfs/hooks/s3-dnbd3root.sh b/modules.d/dnbd3-rootfs/hooks/s3-dnbd3root.sh
index 6c62480a..e79938f6 100755
--- a/modules.d/dnbd3-rootfs/hooks/s3-dnbd3root.sh
+++ b/modules.d/dnbd3-rootfs/hooks/s3-dnbd3root.sh
@@ -111,32 +111,70 @@ if [ -z "$read_only_device" ]; then
 fi
 
 # endregion
-# region find system partition within dnbd3 image
-if [ -z "$SLX_SYSTEM_PARTITION_PREPARATION_SCRIPT" ]; then
-    # Find requested root partition - default to SLX_SYS label
-    read_only_partition="$( slx-tools dev_find_partitions \
-        "$read_only_device" "${SLX_SYSTEM_PARTITION_IDENTIFIER:-SLX_SYS}" )"
-    if [ -z "$SLX_SYSTEM_PARTITION_IDENTIFIER" ]; then
-        if [ -n "$read_only_partition" ]; then
-            # Defaulting to SLX_SYS worked
-            echo "SLX_SYSTEM_PARTITION_IDENTIFIER='SLX_SYS'" >> /etc/openslx
-        else
-            # Aussume there is no partition table
-            read_only_partition="$read_only_device"
+# region find system partition within image
+if [[ "$SLX_SYSTEM_PARTITION_IDENTIFIER" =~ ^\+[0-9]+$ ]]; then
+    # Partition number, e.g. +2 for second partition
+    #
+    num="${SLX_SYSTEM_PARTITION_IDENTIFIER#+}"
+    if [ -b "${read_only_device}p${num}" ]; then
+        read_only_partition="${read_only_device}p${num}"
+    elif [ -b "${read_only_device}${num}" ]; then
+        read_only_partition="${read_only_device}${num}"
+    fi
+else
+    # Find requested root partition by MBRID, GPT label, or GPT type - default to SLX_SYS label
+    #
+    declare -a parts
+    parts=( "${read_only_device}"?* )
+    if [ -b "${parts[0]}" ]; then
+        # There is at least one partition on the device, scan
+        mapfile -t parts < <( slx-tools dev_find_partitions \
+            "$read_only_device" "${SLX_SYSTEM_PARTITION_IDENTIFIER:-SLX_SYS}" )
+        if [ "${#parts[@]}" = 1 ]; then
+            # One match, perfect
+            read_only_partition="${parts[0]}"
+            echo "Found read-only partition by identifier: $read_only_partition"
+        elif [ "${#parts[@]}" = 0 ]; then
+            # Nothing found, scan all partitions. This will include the device itself.
+            parts=( "$read_only_device"* )
         fi
+        # If we found 2 or more matching partitions, they'll be probed below
+    else
+        # No partitions on device - check if it's a file-system
+        parts=( "$read_only_device" )
     fi
+fi
 
-else
-    eval "$SLX_SYSTEM_PARTITION_PREPARATION_SCRIPT"
+if [ -z "$read_only_partition" ]; then
+    # Do a scan
+    echo "Don't know which partition to use, trying all candidates (${parts[*]})"
+    p="/tmp/mounttest"
+    mkdir -p "$p"
+    for part in "${parts[@]}"; do
+        if mount -v -o ro "$part" "$p"; then
+            # See if it looks like a system partition
+            if [ -x "$p/sbin/init" ] || [ -x "$p/lib/systemd/systemd" ]; then
+                umount -lf "$p"
+                echo "Found init on $part, will try to boot off of it."
+                read_only_partition="$part"
+                break
+            fi
+            umount -lf "$p"
+        fi
+    done
 fi
-if [[ -z "$read_only_partition" ]]; then
-    echo "Failed to find unique device with identifier" \
-        "\"${SLX_SYSTEM_PARTITION_IDENTIFIER}\"; matched devices:" \
-        "\"${read_only_partition}\""
+# endregion
+
+if [ -z "$read_only_partition" ]; then
+    echo "Failed to find bootable partition"
+    exit 1
+fi
+if ! [ -b "$read_only_partition" ]; then
+    echo "Bootable partition $read_only_partition does not exist, or is not a block device"
     exit 1
 fi
+
 echo "Using read-only partition: $read_only_partition"
-# endregion
 
 # region add rw layer to dnbd3 image
 # don't be fooled to think we are done, the next part is crucial