ssh mode: stage snapshots on ssh server

Turn backup-zfs into a two-step process:
1. Send snapshots to a server over SSH
2. Receive those snapshots over SSH

Supports a disconnected backup environment where the backup storage host
and the system being backed up don't have to be online at the same time.

Use case: Send snapshots from my home server to my work server while I'm
asleep, then read them over the LAN from my work server to my external
drive while I'm at work.

backup-zfs

@@ -17,6 +17,8 @@ usage() {
 	  -t tag       tag to use for naming snapshots (default: backup-zfs)
 	  -k keep      number of snapshots to keep on src (default: 5)
 	  -d dateopts  options for date(1) - used to name the snapshots (default: +%F_%T)
+	  -s           store mode - output snaps from local fs to ssh server
+	  -r           read mode - read snaps from ssh server to local fs
 	EOF
 	exit $1
 }
@@ -65,11 +67,13 @@ dateopts="+%F_%T"
 keep=5
 verbose=false
 quiet=false
+tossh=false
+fromssh=false
 
 ###
 ### parse options
 ###
-while getopts "hvqk:t:d:" opt ; do
+while getopts "hvqk:t:d:sr" opt ; do
 	case $opt in
 		h) usage 0 ;;
 		v)
@@ -81,11 +85,14 @@ while getopts "hvqk:t:d:" opt ; do
 		k) keep=$OPTARG ;;
 		t) tag=$OPTARG ;;
 		d) dateopts=$OPTARG ;;
+		s) tossh=true ;;
+		r) fromssh=true ;;
 		*) usage 1 ;;
 	esac
 done
 shift $((OPTIND-1))
 date="$(date $dateopts)"
+$tossh && $fromssh && die 1 "-s and -r are mutually exclusive"
 
 ###
 ### parse src & dest host/fs info
@@ -102,6 +109,89 @@ fi
 src="$1"
 dest="$2"
 
+###
+### ssh mode - output snaps from local fs to ssh or read snaps from ssh to local fs
+if $tossh ; then
+	log "sending from local zfs filesystem to SSH server"
+
+	# make sure src exists
+	if [[ $src =~ : ]] ; then
+		die 1 "$src must be a local zfs filesystem"
+	elif [[ $(ZFS "" list -H -o name "$src" 2>/dev/null) != $src ]] ; then
+		die 1 "$src must be a local zfs filesystem"
+	fi
+
+	# split dest to components
+	if [[ $dest =~ : ]] ; then
+		desthost="${dest%:*}"
+		destpath="${dest#*:}"
+	else
+		die 1 "$dest must be ssh host:path"
+	fi
+
+	# get the last src component
+	srcbase="${src##*/}"
+
+	###
+	### create new snapshot on src
+	###
+	cur="$src@${tag}_$date"
+	ZFS "$srchost" snapshot -r "$cur" || die $? "zfs snapshot failed"
+
+	###
+	### get newest snapshot on dest - it must exist on src
+	###
+	#last="$(ZFS "$desthost" list -d 1 -t snapshot -H -S creation -o name $destfs/$srcbase | head -n1 | cut -f2 -d@)"
+	last="$(ssh "$desthost" cat "$destpath/.last")"
+
+	###
+	### send
+	###
+	# refuse to send without a valid .last maker
+	if [[ -z $last ]] ; then
+		die 1 "ssh path contains no .last file"
+	# special case: tagged snapshots exist on dest, but src has rotated through all
+	elif ! ZFS "$srchost" list $src@$last &>/dev/null ; then
+		die 1 "no incremental path from from $src to $dest"
+	# normal case: send incremental
+	else
+		log "sending incremental snapshot from $src to $dest (${last#${tag}_}..${cur#*@${tag}_})"
+		#ZFS "$srchost" send $send_opts -R -I "$last" "$cur" | ZFS "$desthost" receive $recv_opts -Fue "$destfs" || die $? "zfs incremental send failed"
+		ZFS "$srchost" send $send_opts -R -I "$last" "$cur" | ssh "$desthost" "cat > \"$destpath/${tag}_$date.zfssnap\"" || die $? "zfs incremental send failed"
+	fi
+
+	exit
+elif $fromssh ; then
+	log "receving from SSH server to local zfs filesystem"
+
+	# make sure dest exists
+	if [[ $dest =~ : ]] ; then
+		die 1 "$dest must be a local zfs filesystem"
+	elif [[ $(ZFS "" list -H -o name "$dest" 2>/dev/null) != $dest ]] ; then
+		die 1 "$dest must be a local zfs filesystem"
+	fi
+
+	# split src into components
+	if [[ $src =~ : ]] ; then
+		srchost="${src%:*}"
+		srcpath="${src#*:}"
+	else
+		die 1 "$src must be ssh host:path"
+	fi
+
+	###
+	### receive
+	###
+	log "receiving incremental snapshot from $src to $dest"
+	#ZFS "$srchost" send $send_opts -R -I "$last" "$cur" | ZFS "$desthost" receive $recv_opts -Fue "$destfs" || die $? "zfs incremental send failed"
+	for file in $(ssh "$srchost" "find \"$srcpath\" -name \"*.zfssnap\"") ; do
+		ssh "$srchost" "cat \"$file\"" | ZFS "$desthost" receive $recv_opts -Fue "$dest" && ssh "$srchost" "rm \"$file\""
+	done
+
+	exit
+fi
+die 1 "neither -s nor -r was specified"
+
 # discard anything before a colon to get the fs
 srcfs="${src#*:}"
 destfs="${dest#*:}"