Bash script to manage Btrfs snapshots

btrfs-snapshot.sh

#!/bin/bash
set -eo pipefail

SCRIPT_PATH=$0

MOUNT_DEV=/dev/mapper/fedora-root
MOUNT_PATH=/mnt

SNAPSHOTS_SUBVOL=.snapshots
SNAPSHOTS_PATH="$MOUNT_PATH/$SNAPSHOTS_SUBVOL"

SOURCE_SUBVOLS=(base usr_local)

cleanup() {
  mountpoint -q $MOUNT_PATH && umount $MOUNT_PATH
}
trap cleanup EXIT

mount_fs() {
  if ! mountpoint -q $MOUNT_PATH; then
    [ ! -d $MOUNT_PATH ] && mkdir -p $MOUNT_PATH
    mount $MOUNT_DEV $MOUNT_PATH
  fi
}

ACTION=$1
if [ $# -lt 1 ]; then
  echo "Usage: $0 <create|list|restore|delete|replace>" >&2
  exit 1
fi
SNAPSHOT_NAME=$2
if [ -z "$SNAPSHOT_NAME" ]; then
  SNAPSHOT_NAME=latest
fi
SNAPSHOT_PATH=$SNAPSHOTS_PATH/$SNAPSHOT_NAME

create_snapshot() {
  if [ -d $SNAPSHOT_PATH ]; then
    if [ "$SNAPSHOT_NAME" != "latest" ]; then
      echo "Snapshot exists: $SNAPSHOT_NAME" >&2
      exit 1
    fi
    if [ ! -s $SNAPSHOT_PATH/timestamp ]; then
      echo "Latest snapshot missing the timestamp file" >&2
      exit 1
    fi
    SNAPSHOT_TS=$(cat $SNAPSHOT_PATH/timestamp)
    rm $SNAPSHOT_PATH/timestamp
    mv $SNAPSHOT_PATH $SNAPSHOTS_PATH/$SNAPSHOT_TS
  fi
  for SUBVOL in ${SOURCE_SUBVOLS[@]}; do
    [ ! -d $SNAPSHOT_PATH ] && mkdir -p $SNAPSHOT_PATH
    btrfs subvol snap -r $MOUNT_PATH/$SUBVOL $SNAPSHOT_PATH/$SUBVOL
  done
  if [ "$SNAPSHOT_NAME" = "latest" ]; then
    date +%FT%T > $SNAPSHOT_PATH/timestamp
  fi
}

ensure_snapshot() {
  if [ ! -d $SNAPSHOT_PATH ]; then
    echo "Snapshot doesn't exist: $SNAPSHOT_NAME" >&2
    exit 1
  fi
}

delete_snapshot() {
  ensure_snapshot
  for SUBVOL in ${SOURCE_SUBVOLS[@]}; do
    [ -d $SNAPSHOT_PATH/$SUBVOL ] && btrfs subvol delete $SNAPSHOT_PATH/$SUBVOL
  done
  [ -f $SNAPSHOT_PATH/timestamp ] && rm $SNAPSHOT_PATH/timestamp
  rmdir $SNAPSHOT_PATH
}

restore_snapshot() {
  ensure_snapshot
  for SUBVOL in ${SOURCE_SUBVOLS[@]}; do
    rsync -avruP --delete $SNAPSHOT_PATH/$SUBVOL $MOUNT_PATH/$SUBVOL
  done
}

replace_snapshot() {
  [ -d $SNAPSHOT_PATH ] && delete_snapshot
  create_snapshot
}

mount_fs
case "$ACTION" in
  create)
    create_snapshot
    ;;
  restore)
    restore_snapshot
    ;;
  delete)
    delete_snapshot
    ;;
  replace)
    replace_snapshot
    ;;
  list)
    ls -1 $SNAPSHOTS_PATH
    ;;
esac