From bfe4c911a89105cb51745192621b6ddbdb693a81 Mon Sep 17 00:00:00 2001
From: Mike Baynton <mike@mbaynton.com>
Date: Sat, 9 Aug 2014 17:23:02 -0500
Subject: [PATCH] Make --{pre,post}-snapshot optional, add --destroy-only,
 revise docs

---
 src/zfs-auto-snapshot.8  | 26 ++++++++++++++-----
 src/zfs-auto-snapshot.sh | 56 ++++++++++++++++++++++++++++++----------
 2 files changed, 62 insertions(+), 20 deletions(-)

diff --git a/src/zfs-auto-snapshot.8 b/src/zfs-auto-snapshot.8
index a2680cf..51fdc7f 100644
--- a/src/zfs-auto-snapshot.8
+++ b/src/zfs-auto-snapshot.8
@@ -64,14 +64,26 @@ Snapshot named filesystem and all descendants.
 \fB\-v\fR, \fB\-\-verbose\fR
 Print info messages.
 .TP
-\fB\-\-pre-snapshot\fR
-Command to run before snapshotting. It is passed the
-filesystem and snapshot name. If it returns non-zero,
-snapshotting this filesystem is aborted.
+\fB\-\-pre-snapshot\fR=\fICOMMAND\fR
+Command to run before each dataset is snapshotted. 
+It is passed the dataset and snapshot name. If it
+returns non-zero, snapshotting this dataset is 
+aborted.
 .TP
-\fB\-\-post-snapshot\fR
-Command to run after snapshotting. It is passed the
-filesystem and snapshot name.
+\fB\-\-post-snapshot\fR=\fICOMMAND\fR
+Command to run after each dataset is snapshotted. 
+It is passed the dataset and snapshot name.
+.TP
+\fB\-\-destroy-only\fR
+Do not create new snapshots, but do destroy older 
+snapshots. Has no effect unless used with \fB\-k\fR.
+.IP
+A non-obvious use may be constructon of cron jobs or
+scripts that run pre-snapshot command(s), then run 
+zfs-auto-snapshot (without \fB\-k\fR) to quickly
+snapshot all datasets, then run post-snapshot
+command(s) and clean up with zfs-auto-snapshot
+\fB\-\-destroy-only\fR.
 .TP
 name
 Filesystem and volume names, or '//' for all ZFS datasets.
diff --git a/src/zfs-auto-snapshot.sh b/src/zfs-auto-snapshot.sh
index 8ae5f53..2a82c9a 100755
--- a/src/zfs-auto-snapshot.sh
+++ b/src/zfs-auto-snapshot.sh
@@ -41,6 +41,7 @@ opt_skip_scrub=''
 opt_verbose=''
 opt_pre_snapshot=''
 opt_post_snapshot=''
+opt_do_snapshots=1
 
 # Global summary statistics.
 DESTRUCTION_COUNT='0'
@@ -71,6 +72,7 @@ print_usage ()
   -g, --syslog       Write messages into the system log.
   -r, --recursive    Snapshot named filesystem and all descendants.
   -v, --verbose      Print info messages.
+      --destroy-only Only destroy older snapshots, do not create new ones.
       name           Filesystem and volume names, or '//' for all ZFS datasets.
 " 
 }
@@ -150,6 +152,7 @@ do_snapshots () # properties, flags, snapname, oldglob, [targets...]
 	local GLOB="$4"
 	local TARGETS="$5"
 	local KEEP=''
+	local RUNSNAP=1
 
 	# global DESTRUCTION_COUNT
 	# global SNAPSHOT_COUNT
@@ -158,15 +161,21 @@ do_snapshots () # properties, flags, snapname, oldglob, [targets...]
 
 	for ii in $TARGETS
 	do
-		do_run "$opt_pre_snapshot $ii $NAME"
-		if [ $? -eq 0 ] && do_run "zfs snapshot $PROPS $FLAGS '$ii@$NAME'"
+		if [ -n "$opt_do_snapshots" ]
 		then
-			do_run "$opt_post_snapshot $ii $NAME"
-			SNAPSHOT_COUNT=$(( $SNAPSHOT_COUNT + 1 ))
-		else
-			WARNING_COUNT=$(( $WARNING_COUNT + 1 ))
-			continue
-		fi 
+			if [ "$opt_pre_snapshot" != "" ]
+			then
+				do_run "$opt_pre_snapshot $ii $NAME" || RUNSNAP=0
+			fi
+			if [ $RUNSNAP -eq 1 ] && do_run "zfs snapshot $PROPS $FLAGS '$ii@$NAME'"
+			then
+				[ "$opt_post_snapshot" != "" ] && do_run "$opt_post_snapshot $ii $NAME"
+				SNAPSHOT_COUNT=$(( $SNAPSHOT_COUNT + 1 ))
+			else
+				WARNING_COUNT=$(( $WARNING_COUNT + 1 ))
+				continue
+			fi 
+		fi
 
 		# Retain at most $opt_keep number of old snapshots of this filesystem,
 		# including the one that was just recently created.
@@ -202,7 +211,7 @@ GETOPT=$(getopt \
   --longoptions=default-exclude,dry-run,fast,skip-scrub,recursive \
   --longoptions=event:,keep:,label:,prefix:,sep: \
   --longoptions=debug,help,quiet,syslog,verbose \
-  --longoptions=pre-snapshot:,post-snapshot: \
+  --longoptions=pre-snapshot:,post-snapshot:,destroy-only \
   --options=dnshe:l:k:p:rs:qgv \
   -- "$@" ) \
   || exit 128
@@ -321,6 +330,10 @@ do
 			opt_post_snapshot="$2"
 			shift 2
 			;;
+		(--destroy-only)
+			opt_do_snapshots=''
+			shift 1
+			;;
 		(--)
 			shift 1
 			break
@@ -525,11 +538,28 @@ SNAPNAME="$opt_prefix${opt_label:+$opt_sep$opt_label}-$DATE"
 # The expression for matching old snapshots.  -YYYY-MM-DD-HHMM
 SNAPGLOB="$opt_prefix${opt_label:+?$opt_label}????????????????"
 
-test -n "$TARGETS_REGULAR" \
-  && print_log info "Doing regular snapshots of $TARGETS_REGULAR"
+if [ -n "$opt_do_snapshots" ]
+then
+	test -n "$TARGETS_REGULAR" \
+	  && print_log info "Doing regular snapshots of $TARGETS_REGULAR"
 
-test -n "$TARGETS_RECURSIVE" \
-  && print_log info "Doing recursive snapshots of $TARGETS_RECURSIVE"
+	test -n "$TARGETS_RECURSIVE" \
+	  && print_log info "Doing recursive snapshots of $TARGETS_RECURSIVE"
+
+	if test -n "$opt_keep" && [ "$opt_keep" -ge "1" ]
+	then
+		print_log info "Destroying all but the newest $opt_keep snapshots of each dataset."
+	fi
+elif test -n "$opt_keep" && [ "$opt_keep" -ge "1" ]
+then
+	test -n "$TARGETS_REGULAR" \
+	  && print_log info "Destroying all but the newest $opt_keep snapshots of $TARGETS_REGULAR"
+
+	test -n "$TARGETS_RECURSIVE" \
+	  && print_log info "Recursively destroying all but the newest $opt_keep snapshots of $TARGETS_RECURSIVE"
+else
+	print_log notice "Only destroying snapshots, but count of snapshots to preserve not given. Nothing to do."
+fi
 
 test -n "$opt_dry_run" \
   && print_log info "Doing a dry run. Not running these commands..."