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#!/bin/bash
# Snapshot the root dataset before a pacman transaction, then prune to the most
# recent $KEEP pre-pacman snapshots. Run from the zfs-snapshot.hook pacman hook
# (PreTransaction). Sanoid doesn't manage these (they aren't autosnap_ names),
# so retention is enforced here at creation time.
#
# Defaults match the live zroot layout; the ZFS_PRE_* env vars override them so
# the pruning logic is unit-testable against a fake zfs on PATH.
POOL="${ZFS_PRE_POOL:-zroot}"
DATASET="${ZFS_PRE_DATASET:-$POOL/ROOT/default}"
LOCKFILE="${ZFS_PRE_LOCKFILE:-/tmp/.zfs-pre-snapshot.lock}"
MIN_INTERVAL="${ZFS_PRE_MIN_INTERVAL:-60}"
KEEP="${ZFS_PRE_KEEP:-10}" # pre-pacman snapshots to retain (recent-transaction rollback)
# Skip if a snapshot was created within the last $MIN_INTERVAL seconds. A single
# pacman invocation can fire several transactions; this stops a burst of them
# from each cutting a near-identical snapshot.
if [ -f "$LOCKFILE" ]; then
last=$(stat -c %Y "$LOCKFILE" 2>/dev/null || echo 0)
now=$(date +%s)
if (( now - last < MIN_INTERVAL )); then
exit 0
fi
fi
TIMESTAMP=$(date +%Y-%m-%d_%H-%M-%S)
SNAPSHOT_NAME="pre-pacman_$TIMESTAMP"
if zfs snapshot "$DATASET@$SNAPSHOT_NAME"; then
echo "Created snapshot: $DATASET@$SNAPSHOT_NAME"
touch "$LOCKFILE"
# Keep only the most recent $KEEP pre-pacman snapshots; destroy older ones.
zfs list -H -o name -t snapshot -s creation "$DATASET" 2>/dev/null \
| grep '@pre-pacman_' \
| head -n -"$KEEP" \
| while read -r old; do
zfs destroy "$old" && echo "Pruned old snapshot: $old"
done
else
echo "Warning: Failed to create snapshot" >&2
fi
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