Allow override of dstdir with subvolume delta and add snapshot with retention

btrfs/btrfs-subvolume-delta

@@ -3,7 +3,7 @@ set -e
 
 SRC="$1"
 RECV="$2"
-DSTDIR="$SRC/.snap"
+DSTDIR="$SRC/${3:-.snap}"
 CDATE="$(date '+%s')"
 PREV="prev"
 CUR="cur"

btrfs/snapshot

@@ -0,0 +1,18 @@
+#!/bin/sh
+#
+# BTRFS rolling snapshots
+# CC0 ~caskd
+
+: ${SRC:?'Source not defined'}
+: ${DEST:?'Destination not defined'}
+: ${NAME:?'Name not defined'}
+: ${SN:?'Selection name not defined'}
+: ${RT:?'Retention time not defined'}
+
+s="$SRC"
+d="$DEST/$SN/$NAME"
+
+mkdir -p "${d%/*}"
+find "$DEST" -mindepth 1 -maxdepth 1 -type d -ctime +"$RT" -exec echo "{}/$NAME" ';' | xargs btrfs subvolume del
+btrfs subvolume delete "$d"
+btrfs subvolume snapshot -r "$s" "$d"