1 files changed, 113 insertions, 0 deletions

diff --git a/push-btrfs b/push-btrfs
new file mode 100755
index 0000000..5e9b537
--- /dev/null
+++ b/push-btrfs
@@ -0,0 +1,113 @@
+#!/bin/bash
+MAX_AGE_SECONDS=60
+CONFIG_DIR=/etc/btrfs-backup/remotes
+
+die()
+{
+        printf 'Error: %s\n' "$*" >&2
+        exit 1
+}
+
+read_config()
+{
+        eval config="($(jq -r '. | to_entries | .[] | "[\"" + .key + "\"]=" + (.value | @sh)'))"
+}
+
+check_dependencies()
+{
+        for c in flock jq btrfs pv realpath stat date mv ln rm
+        do
+                command -v $c >/dev/null
+        done
+}
+
+check_user_is_root()
+{
+        [ "$UID" = 0 ]
+}
+
+is_subvolume()
+{
+        btrfs subvolume show -- "$1" >/dev/null 2>&1
+}
+
+get_age()
+{
+        now=$(date +%s)
+        then=$(stat -L -c %Y "$1")
+        echo $((now - then))
+}
+
+btrfs_receive()
+{
+        ssh -- "${1%%:*}" btrfs receive -- "${1#*:}"
+}
+
+set -e
+check_dependencies
+check_user_is_root
+
+if [ $# = 1 ]
+then
+        case "$1" in
+                '' ) die 'config file name is blank' ;;
+                */*) die 'config file name must not contain "/"' ;;
+                *.json) ;;
+                *) die "config file name must end in '.json'" ;;
+        esac
+        config_file=$CONFIG_DIR/$1
+        config_file_temp=$CONFIG_DIR/.$1~tmp
+else
+        echo "Usage: $0 <config.json>" >&2
+        exit 1
+fi
+
+[ -r "$config_file" ] || die "config file does not exist: $config_file"
+exec 3<>"$config_file"
+flock -n 3
+declare -A config
+read_config <&3
+
+src=${config[source]}
+dst=${config[destination]}
+remote_head=${config[head]}
+
+case "$dst" in
+        *:/*) ;;
+        /*) dst=localhost:$dst ;;
+        *) die "Invalid destination: $dst" ;;
+esac
+
+is_subvolume "$src"
+
+if [ "$(get_age "$remote_head")" -le "$MAX_AGE_SECONDS" ]
+then
+        echo "Up-to-date." >&2
+        exit
+else
+        new_snapshot=${src%/}/.snapshot~$(date -Ins)
+        btrfs subvolume snapshot -r -- "$src" "$new_snapshot"
+fi
+
+btrfs send ${remote_head:+ -p "$remote_head"} -- "$new_snapshot" | pv | btrfs_receive "$dst"
+jq --arg h "$new_snapshot" '. | .head=$h' <"$config_file" >"$config_file_temp"
+mv -T -- "$config_file_temp" "$config_file"
+
+if [ "$remote_head" ]
+then
+        btrfs subvolume delete "$remote_head"
+fi
+
+### OK, basic idea:
+#
+## the system has a list of source subvolumes
+## each source subvolume has a snapshot period
+## each source subvolume has a list of subscribers
+## each source subvolume has an ordered list of its snapshots
+## each subscriber has a last-received snapshot (if any)
+
+# when a subvolume's last snapshot is older than the configured period, a new snapshot is created
+# when a subvolume has subscribers whose last snapshot is out-of-date, a snapshot is pushed (using the common ancestor)
+# the subscriber's last snapshot is then updated
+# if there are no subscriber's holding open a snapshot which is not the latest snapshot, then it is deleted
+