improve retain-snapshots

1 files changed, 108 insertions, 0 deletions

diff --git a/retain-snapshots b/retain-snapshots
new file mode 100755
index 0000000..86f0120
--- /dev/null
+++ b/retain-snapshots
@@ -0,0 +1,108 @@
+#!/bin/bash
+default_retain_years=7
+retain_years= # TODO: read retain_years from .propagation
+
+use_clock_time= # Delete according to clock time (WARNING: eventually deletes all data)
+
+
+# Never edit this regex.
+# Generated via: date -Ins | sed 's/[0-9]/[0-9]/g'
+datetime_regexp='[0-9][0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9]T[0-9][0-9]:[0-9][0-9]:[0-9][0-9],[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]-[0-9][0-9]:[0-9][0-9]'
+
+snapshot_prefix='.snapshot~'
+
+main()
+{
+        [ $# = 1 ] || exit
+        case "$1" in
+                /*) ;;
+                *) exit 1 ;;
+        esac
+
+        # Using `cd "$1"` and `find .` allows the path to contain
+        # newlines, while simple `find "$1"` would break the script.
+        # NB: Our snapshot name itself never contains whitespace.
+        cd "$1" || exit
+        find . -maxdepth 1 -type d -name "$snapshot_prefix""$datetime_regexp" | sort -rn | retain
+}
+
+is_readonly_subvolume()
+{
+        [ -d "$1" ]
+        btrfs subvolume show -- "$1" | sed -En -e'/^\tFlags:.*\breadonly\b/{q0}' -e'${q1}'
+}
+
+btrfs_subvolume_delete()
+{
+        >&2 echo btrfs subvolume delete "$@"
+}
+
+# Delete all snapshots that we do not retain.
+# The retention period is specified in a ".propagation" file.
+# If not specified it is 7 years.
+# Retain the most recent snapshot within any     year   of the   last 7 years.
+# Retain the most recent snapshot within any    month   of the   last 365 days.
+# Retain the most recent snapshot within any      day   of the   last 7 days.
+# Retain the most recent snapshot within any     hour   of the   last 24 hours.
+# Retain the most recent snapshot within any   minute   of the   last hour.
+# Retain any snapshot created in the last minute.
+
+retain()
+{
+        2>/dev/null [ "$retain_years" -ge 1 ] || retain_years=$default_retain_years
+
+        _year= _month= _day= _hour= _minute= _second= _nanosecond=
+        now=
+        if [ "$use_clock_time" ]
+        then
+                now=$(date +%s)
+        fi
+        while read line
+        do
+                is_readonly_subvolume "$line" || break
+                dateline=${line#*/"$snapshot_prefix"}
+                [ "$dateline" != "$line" ]
+                before=$(date -d "$dateline" +%s)
+                [ "$now" ] || now=$before
+                age=$((now - before))
+
+                IFS='~-T:,' read year month day hour minute second nanosecond <<< "$dateline"
+
+                keep=
+                if [ "$year" != "$_year" ] && [ "$age" -lt $((retain_years * 366 * 24 * 60 * 60)) ]
+                then
+                        keep="$year -> $line"
+                elif [ "$month" != "$_month" ] && [ "$age" -lt $((366 * 24 * 60 * 60)) ]
+                then
+                        keep="$year-$month -> $line"
+                elif [ "$day" != "$_day" ] && [ "$age" -lt $((7 * 24 * 60 * 60)) ]
+                then
+                        keep="$year-$month-$day -> $line"
+                elif [ "$hour" != "$_hour" ] && [ "$age" -lt $((24 * 60 * 60)) ]
+                then
+                        keep="$year-$month-${day}T$hour -> $line"
+                elif [ "$minute" != "$_minute" ] && [ "$age" -lt $((60 * 60)) ]
+                then
+                        keep="$year-$month-${day}T$hour:$minute -> $line"
+                elif [ "$age" -lt 60 ]
+                then
+                        keep="recent -> $line"
+                fi
+
+                if [ "$keep" ]
+                then
+                        echo "$keep" >&2
+                else
+                        btrfs_subvolume_delete -- "$line"
+                fi
+
+                _year=$year
+                _month=$month
+                _day=$day
+                _hour=$hour
+                _minute=$minute
+                _second=$second
+        done
+}
+
+main "$@"