Implement --send-fallback for the snapshot replication.

This allows a --send-incr to fallback to --send-full if it can't find
an earlier snapshot.

src/zfs-auto-snapshot.8

@@ -52,6 +52,11 @@ Send zfs full backup to remote hostname (or IP address) and put it in  remote po
 \fB\-\-send\-incr\fR=[\fIremote host\fR]:[\fIremote pool\fR]
 Send zfs incremental backup to remote hostname (or IP address) and put it in remote pool.
 .TP
+\fB\-\-send\-fallback\fR
+Allow to fallback from incremental to full snapshot replication.
+.sp
+This implies \fI-R\fR to \fBzfs send\fR and \fI-F\fR to \fBzfs receive\fR.
+.TP
 \fB\-\-send\-opts\fR=\fIOPTS\fR
 Option(s) passed to 'zfs send'.
 .TP

src/zfs-auto-snapshot.sh

@@ -41,6 +41,7 @@ opt_send_opts=''
 opt_recv_opts=''
 opt_send_ssh_opts=''
 opt_send_mbuf_opts=''
+opt_send_fallback=''
 opt_sep='_'
 opt_setauto=''
 opt_syslog=''
@@ -77,6 +78,7 @@ print_usage ()
   -q, --quiet           Suppress warnings and notices at the console.
       --send-full=F     Send zfs full backup. Unimplemented.
       --send-incr=F     Send zfs incremental backup. Unimplemented.
+      --send-fallback   Fallback from incremental to full if needed.
       --send-opts=F     Option(s) passed to 'zfs send'.
       --recv-opts=F     Option(s) passed to 'zfs receive'.
       --send-ssh-opts   Option(s) passed to 'ssh'.
@@ -231,8 +233,8 @@ do_send () # snapname, oldglob
 	local jj
 
 	[ -n "$opt_send_mbuf_opts" ] && remote="mbuffer $opt_send_mbuf_opts |"
-	remote="$remote ssh $opt_send_ssh_opts $opt_send_host "
-	remote="$remote zfs receive $opt_recv_opts $opt_recv_pool"
+	remote="$remote ssh $opt_send_ssh_opts $opt_send_host"
+	remote="$remote zfs receive $opt_recv_opts"
 
 	# STEP 1: Go throug all snapshots we've created
 	for ii in $SNAPS_DONE
@@ -263,22 +265,33 @@ do_send () # snapname, oldglob
 		#         1: We change from incremental to full.
 		#         2: We accept that the user have said INCR, and stick with
 		#            it.
-		if [ "$opt_send_type" = "incr" -a -z "$last_snap" ]; then
+		#       Normally we do point 2, but if --send-fallback is specified,
+		#       we allow it and convert to a full send instead.
+		if [ "$opt_send_type" = "incr" -a -z "$last_snap" -a -z "$opt_send_fallback" ]; then
 			if [ -n "$opt_verbose" ]; then
 				echo "WARNING: No previous snapshots exist but we where called"
 				echo "         with --send-incr. Can not continue."
 				echo "         Please rerun with --send-full."
+				echo "         Or use --send-fallback."
 			fi
 			return 1
 		fi
 
-		if [ -n "$opt_recursive" -a -n "$last_snap" ]; then
+		if [ -n "$opt_recursive" ]; then
 			# STEP 3: Again, go through ALL snapshots that exists, but this
 			#         time only look for the snapshots that 'starts with'
 			#         the dataset/volume in question AND 'ends with'
 			#         the exact snapshot name/date in step 2.
 			for jj in $SNAPSHOTS_OLD
 			do
+				# When trying to find snapshots recurively, we MUST have a 'last_snap'
+				# value. Othervise, it will match ALL snapshots for dset (if we had
+				# used '"^$dset.*@$GLOB" only).
+				if [ -z "$last_snap" ] && echo "$jj" | grep -qE "^$dset.*@$GLOB"; then
+					# Use this as last snapshot name
+					last_snap="${jj#*@}"
+				fi
+
 				if echo "$jj" | grep -qE "^$dset.*@$last_snap"; then
 					SNAPS_SEND="$SNAPS_SEND
 $jj"
@@ -297,9 +310,15 @@ $jj"
 
 			if [ $RUNSEND -eq 1 ]; then
 				if [ "$opt_send_type" = "incr" ]; then
-					do_run "zfs send $opt_send_opts -i $jj $ii | $remote" || RUNSEND=0
+					if [ "$jj" = "$ii" -a -n "$opt_send_fallback" ]; then
+						do_run "zfs send $opt_send_opts -R $ii | $remote -F $opt_recv_pool" \
+							|| RUNSEND=0
+					else
+						do_run "zfs send $opt_send_opts -i $jj $ii | $remote $opt_recv_pool" \
+							|| RUNSEND=0
+					fi
 				else
-					do_run "zfs send $opt_send_opts -R $jj | $remote" || RUNSEND=0
+					do_run "zfs send $opt_send_opts -R $jj | $remote $opt_recv_pool" || RUNSEND=0
 				fi
 			fi
 
@@ -321,6 +340,7 @@ GETOPT=$(getopt \
   --longoptions=pre-snapshot:,post-snapshot:,destroy-only \
   --longoptions=send-full:,send-incr:,send-opts:,recv-opts: \
   --longoptions=send-ssh-opts:,send-mbuf-opts:,pre-send:,post-send: \
+  --longoptions=send-fallback \
   --options=dnshe:l:k:p:rs:qgv \
   -- "$@" ) \
   || exit 128
@@ -421,6 +441,10 @@ do
 			opt_recv_pool=$(echo "$2" | sed 's,.*:,,')
 			shift 2
 			;;
+		(--send-fallback)
+			opt_send_fallback=1
+			shift 1
+			;;
 		(--send-opts)
 			opt_send_opts="$2"
 			shift 2