Fix issues where cryptsetup would fail to unmount

There were occasions where removing the backup drive would confuse luks
and prevent re-mounting. This fixes the issue by attempting to luks
close and open the drive before mounting, thereby correcting any issues
where the drive would stick.

ansible/arch_backup/templates/btrfs_backup.sh.j2

@@ -0,0 +1,101 @@
+#!/bin/bash
+
+# Backup info
+export BACKUP_DRIVE_UUID={{ disk.uuid }}
+export BACKUP_DRIVE={{ disk.name }}
+export BACKUP_DRIVE_PASSWORD={{ disk.password }}
+
+# For notifications
+export DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/{{ notifications.user.uid }}/bus
+export USER={{ notifications.user.name }}
+
+export SOURCE_DIR=${SOURCE_DIR:=/}
+# Fix basename / showing up as "/" -> change to "root"
+if [ $(basename $SOURCE_DIR) = / ]; then
+    export SNAPSHOT_PREFIX=${SNAPSHOT_PREFIX:=root}
+else
+    export SNAPSHOT_PREFIX=${SNAPSHOT_PREFIX:=$(basename $SOURCE_DIR)}
+fi
+# Set snapshot prefix based on basename
+export SNAPSHOT_TIME=$(date +"%y_%m_%d-%H.%M")
+export SNAPSHOT_NAME=$SNAPSHOT_PREFIX-$SNAPSHOT_TIME
+export SNAPSHOT_DIR=${SNAPSHOT_DIR:=/.snapshots}
+export LATEST=$SNAPSHOT_PREFIX-latest
+export BACKUP_DRIVE=backup0
+export BACKUP_DRIVE_MNT=${BACKUP_DRIVE_MNT:=/mnt/$BACKUP_DRIVE}
+export BACKUP_DIR=${BACKUP_DIR:=/mnt/$BACKUP_DRIVE/$(hostname)}
+
+# Show snapshot settings
+echo "SOURCE_DIR: $SOURCE_DIR"
+echo "SNAPSHOT_PREFIX: $SNAPSHOT_PREFIX"
+echo "SNAPSHOT_TIME: $SNAPSHOT_TIME"
+echo "SNAPSHOT_NAME: $SNAPSHOT_NAME"
+echo "SNAPSHOT_DIR: $SNAPSHOT_DIR"
+echo "LATEST: $LATEST"
+echo "BACKUP_DRIVE_MNT: $BACKUP_DRIVE_MNT"
+echo "BACKUP_DIR: $BACKUP_DIR"
+
+# Create readonly snapshot
+btrfs subvolume snapshot -r $SOURCE_DIR $SNAPSHOT_DIR/$SNAPSHOT_NAME
+
+# Attempt to mount backup disk
+# Check if backup disk is mounted
+mountpoint $BACKUP_DRIVE_MNT
+if [ $? != 0 ]; then
+    cryptsetup luksClose $BACKUP_DRIVE
+    cryptsetup luksOpen /dev/disk/by-uuid/$BACKUP_DRIVE_UUID $BACKUP_DRIVE --key-file=$BACKUP_DRIVE_PASSWORD
+    mount $BACKUP_DRIVE_MNT
+fi
+
+# Check if backup disk is mounted
+mountpoint $BACKUP_DRIVE_MNT
+if [ $? = 0 ]; then # backup drive mounted
+    if [ ! -d $BACKUP_DIR ]; then
+        mkdir -p $BACKUP_DIR
+    fi
+    # Sync latest backups
+    # The "latest" symlinks can get out of sync for a variety of reasons,
+    # including backups run while the disk is unplugged.
+    # They must be kept in sync so that snapshots are sent with a parent
+    # that actually exists on the backup drive
+    #
+    # In order to keep them in sync we'll do the following:
+    # 1. Check the <backup>-latest on the backup drive matches
+    #    <backup>-latest in the snapshot directory
+    # 2. If they don't match, assume the backup drive has the correct
+    #    snapshot. Replace the <backup>-latest symlink in the snapshots
+    #    directory with the one from the backup drive
+    #
+    # First check if the symlinks exist
+    if [ -L $SNAPSHOT_DIR/$LATEST ] && [ -L $BACKUP_DIR/$LATEST ]; then
+        # Get the actual name of the latest backup
+        LATEST_SNAPSHOT=$(basename $(readlink $SNAPSHOT_DIR/$LATEST))
+        LATEST_BACKUP=$(basename $(readlink $BACKUP_DIR/$LATEST))
+        # If the latest backups don't match
+        if [ $LATEST_SNAPSHOT != $LATEST_BACKUP ]
+        then
+            echo "Detected drift. Synchronizing latest snapshot with backup. Set to $LATEST_BACKUP."
+            # Remove and replace the snapshot directory's latest
+            rm $SNAPSHOT_DIR/$LATEST
+            ln -s $SNAPSHOT_DIR/$LATEST_BACKUP $SNAPSHOT_DIR/$LATEST
+        fi
+    fi
+
+    # If we have a latest, use it as the parent
+    if [ -L $BACKUP_DIR/$LATEST ]; then
+        btrfs send -p $SNAPSHOT_DIR/$LATEST $SNAPSHOT_DIR/$SNAPSHOT_NAME | btrfs receive $BACKUP_DIR
+    else
+        btrfs send $SNAPSHOT_DIR/$SNAPSHOT_NAME | btrfs receive $BACKUP_DIR
+    fi
+
+    # Update latest in backup dir
+    rm -f $BACKUP_DIR/$LATEST
+    ln -s $BACKUP_DIR/$SNAPSHOT_NAME $BACKUP_DIR/$LATEST
+    sudo -E -u $USER notify-send "Backup complete" "Snapshot $SNAPSHOT_NAME completed successfully"
+else
+    sudo -E -u $USER notify-send "Backup failed" "$BACKUP_DRIVE_MNT not mounted. Snapshot $SNAPSHOT_NAME not synced" -u critical
+fi
+
+# Update latest in snapshot dir
+rm -f $SNAPSHOT_DIR/$LATEST
+ln -s $SNAPSHOT_DIR/$SNAPSHOT_NAME $SNAPSHOT_DIR/$LATEST