--- xen-4.10.0/tools/ocaml/libs/xc/xenctrl.ml.orig	2017-12-13 11:37:59.000000000 +0000
+++ xen-4.10.0/tools/ocaml/libs/xc/xenctrl.ml	2017-12-16 15:01:29.683432280 +0000
@@ -263,7 +263,7 @@
 (* coredump *)
 let coredump xch domid fd =
 	let dump s =
-		let wd = Unix.write fd s 0 (String.length s) in
+		let wd = Unix.write fd (Bytes.of_string s) 0 (String.length s) in
 		if wd <> String.length s then
 			failwith "error while writing";
 		in
--- xen-4.10.0/tools/ocaml/libs/xb/xb.ml.orig	2017-12-13 11:37:59.000000000 +0000
+++ xen-4.10.0/tools/ocaml/libs/xb/xb.ml	2017-12-16 16:30:25.195726461 +0000
@@ -40,7 +40,7 @@
 
 type backend = Fd of backend_fd | Xenmmap of backend_mmap
 
-type partial_buf = HaveHdr of Partial.pkt | NoHdr of int * string
+type partial_buf = HaveHdr of Partial.pkt | NoHdr of int * bytes
 
 type t =
 {
@@ -52,7 +52,7 @@
 }
 
 let init_partial_in () = NoHdr
-	(Partial.header_size (), String.make (Partial.header_size()) '\000')
+	(Partial.header_size (), Bytes.make (Partial.header_size()) '\000')
 
 let reconnect t = match t.backend with
 	| Fd _ ->
@@ -76,7 +76,9 @@
 	rd
 
 let read_mmap back con s len =
-	let rd = Xs_ring.read back.mmap s len in
+	let stmp = String.make len (char_of_int 0) in
+	let rd = Xs_ring.read back.mmap stmp len in
+	Bytes.blit_string stmp 0 s 0 rd;
 	back.work_again <- (rd > 0);
 	if rd > 0 then
 		back.eventchn_notify ();
@@ -100,7 +98,7 @@
 
 let write con s len =
 	match con.backend with
-	| Fd backfd     -> write_fd backfd con s len
+	| Fd backfd     -> write_fd backfd con (Bytes.of_string s) len
 	| Xenmmap backmmap -> write_mmap backmmap con s len
 
 (* NB: can throw Reconnect *)
@@ -131,7 +129,7 @@
 		| NoHdr   (i, buf)    -> i in
 
 	(* try to get more data from input stream *)
-	let s = String.make to_read '\000' in
+	let s = Bytes.make to_read '\000' in
 	let sz = if to_read > 0 then read con s to_read else 0 in
 
 	(
@@ -139,7 +137,7 @@
 	| HaveHdr partial_pkt ->
 		(* we complete the data *)
 		if sz > 0 then
-			Partial.append partial_pkt s sz;
+			Partial.append partial_pkt (Bytes.to_string s) sz;
 		if Partial.to_complete partial_pkt = 0 then (
 			let pkt = Packet.of_partialpkt partial_pkt in
 			con.partial_in <- init_partial_in ();
@@ -149,9 +147,9 @@
 	| NoHdr (i, buf)      ->
 		(* we complete the partial header *)
 		if sz > 0 then
-			String.blit s 0 buf (Partial.header_size () - i) sz;
+			Bytes.blit s 0 buf (Partial.header_size () - i) sz;
 		con.partial_in <- if sz = i then
-			HaveHdr (Partial.of_string buf) else NoHdr (i - sz, buf)
+			HaveHdr (Partial.of_string (Bytes.to_string buf)) else NoHdr (i - sz, buf)
 	);
 	!newpacket
 
--- xen-4.10.0/tools/ocaml/libs/xb/xb.mli.orig	2018-03-09 19:02:47.853172392 +0000
+++ xen-4.10.0/tools/ocaml/libs/xb/xb.mli	2017-12-13 11:37:59.000000000 +0000
@@ -65,7 +65,7 @@
 }
 type backend_fd = { fd : Unix.file_descr; }
 type backend = Fd of backend_fd | Xenmmap of backend_mmap
-type partial_buf = HaveHdr of Partial.pkt | NoHdr of int * string
+type partial_buf = HaveHdr of Partial.pkt | NoHdr of int * bytes
 type t = {
   backend : backend;
   pkt_in : Packet.t Queue.t;
@@ -76,10 +76,10 @@
 val init_partial_in : unit -> partial_buf
 val reconnect : t -> unit
 val queue : t -> Packet.t -> unit
-val read_fd : backend_fd -> 'a -> string -> int -> int
-val read_mmap : backend_mmap -> 'a -> string -> int -> int
-val read : t -> string -> int -> int
-val write_fd : backend_fd -> 'a -> string -> int -> int
+val read_fd : backend_fd -> 'a -> bytes -> int -> int
+val read_mmap : backend_mmap -> 'a -> bytes -> int -> int
+val read : t -> bytes -> int -> int
+val write_fd : backend_fd -> 'a -> bytes -> int -> int
 val write_mmap : backend_mmap -> 'a -> string -> int -> int
 val write : t -> string -> int -> int
 val output : t -> bool
--- xen-4.10.0/tools/ocaml/xenstored/stdext.ml.orig	2017-12-13 11:37:59.000000000 +0000
+++ xen-4.10.0/tools/ocaml/xenstored/stdext.ml	2017-12-16 16:39:35.645109021 +0000
@@ -122,7 +122,7 @@
 		let pid = Unix.getpid () in
 		let buf = string_of_int pid ^ "\n" in
 		let len = String.length buf in
-		if Unix.write fd buf 0 len <> len 
+		if Unix.write fd (Bytes.of_string buf) 0 len <> len 
 		then failwith "pidfile_write failed";
 	)
 	(fun () -> Unix.close fd)
diff -ur xen-4.10.0.orig/tools/ocaml/xenstored/logging.ml xen-4.10.0/tools/ocaml/xenstored/logging.ml
--- xen-4.10.0.orig/tools/ocaml/xenstored/logging.ml	2017-12-13 11:37:59.000000000 +0000
+++ xen-4.10.0/tools/ocaml/xenstored/logging.ml	2017-12-16 23:24:47.402606119 +0000
@@ -60,11 +60,11 @@
 let truncate_line nb_chars line = 
 	if String.length line > nb_chars - 1 then
 		let len = max (nb_chars - 1) 2 in
-		let dst_line = String.create len in
-		String.blit line 0 dst_line 0 (len - 2);
-		dst_line.[len-2] <- '.'; 
-		dst_line.[len-1] <- '.';
-		dst_line
+		let dst_line = Bytes.create len in
+		Bytes.blit_string line 0 dst_line 0 (len - 2);
+		Bytes.set dst_line (len-2) '.'; 
+		Bytes.set dst_line (len-1) '.';
+		Bytes.to_string dst_line
 	else line
 
 let log_rotate ref_ch log_file log_nb_files =
@@ -252,13 +252,13 @@
 	*)
 
 let sanitize_data data =
-	let data = String.copy data in
-	for i = 0 to String.length data - 1
+	let data = Bytes.copy data in
+	for i = 0 to Bytes.length data - 1
 	do
-		if data.[i] = '\000' then
-			data.[i] <- ' '
+		if Bytes.get data i = '\000' then
+			Bytes.set data i ' '
 	done;
-	String.escaped data
+	String.escaped (Bytes.to_string data)
 
 let activate_access_log = ref true
 let access_log_destination = ref (File (Paths.xen_log_dir ^ "/xenstored-access.log"))
@@ -291,7 +291,7 @@
 				let date = string_of_date() in
 				let tid = string_of_tid ~con tid in
 				let access_type = string_of_access_type access_type in
-				let data = sanitize_data data in
+				let data = sanitize_data (Bytes.of_string data) in
 				let prefix = prefix !access_log_destination date in
 				let msg = Printf.sprintf "%s %s %s %s" prefix tid access_type data in
 				logger.write ~level msg)
diff -ur xen-4.10.0.orig/tools/ocaml/xenstored/utils.ml xen-4.10.0/tools/ocaml/xenstored/utils.ml
--- xen-4.10.0.orig/tools/ocaml/xenstored/utils.ml	2017-12-13 11:37:59.000000000 +0000
+++ xen-4.10.0/tools/ocaml/xenstored/utils.ml	2017-12-16 23:26:24.968649002 +0000
@@ -45,23 +45,23 @@
 
 let hexify s =
 	let hexseq_of_char c = sprintf "%02x" (Char.code c) in
-	let hs = String.create (String.length s * 2) in
+	let hs = Bytes.create (String.length s * 2) in
 	for i = 0 to String.length s - 1
 	do
 		let seq = hexseq_of_char s.[i] in
-		hs.[i * 2] <- seq.[0];
-		hs.[i * 2 + 1] <- seq.[1];
+		Bytes.set hs (i * 2) seq.[0];
+		Bytes.set hs (i * 2 + 1) seq.[1];
 	done;
-	hs
+	Bytes.to_string hs
 
 let unhexify hs =
 	let char_of_hexseq seq0 seq1 = Char.chr (int_of_string (sprintf "0x%c%c" seq0 seq1)) in
-	let s = String.create (String.length hs / 2) in
-	for i = 0 to String.length s - 1
+	let s = Bytes.create (String.length hs / 2) in
+	for i = 0 to Bytes.length s - 1
 	do
-		s.[i] <- char_of_hexseq hs.[i * 2] hs.[i * 2 + 1]
+		Bytes.set s i (char_of_hexseq hs.[i * 2] hs.[i * 2 + 1])
 	done;
-	s
+	Bytes.to_string s
 
 let trim_path path =
 	try
@@ -84,10 +84,10 @@
 
 let read_file_single_integer filename =
 	let fd = Unix.openfile filename [ Unix.O_RDONLY ] 0o640 in
-	let buf = String.make 20 (char_of_int 0) in
+	let buf = Bytes.make 20 (char_of_int 0) in
 	let sz = Unix.read fd buf 0 20 in
 	Unix.close fd;
-	int_of_string (String.sub buf 0 sz)
+	int_of_string (Bytes.to_string (Bytes.sub buf 0 sz))
 
 let path_complete path connection_path =
 	if String.get path 0 <> '/' then