From f13fe5903361953e4ccf8602b9c8df7e64568d55 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Edwin=20T=C3=B6r=C3=B6k?= <edvin.torok@citrix.com>
Date: Wed, 12 Oct 2022 19:13:02 +0100
Subject: tools/ocaml: Change Xb.input to return Packet.t option
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The queue here would only ever hold at most one element.  This will simplify
follow-up patches.

This is part of XSA-326.

Reported-by: Julien Grall <jgrall@amazon.com>
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>

diff --git a/tools/ocaml/libs/xb/xb.ml b/tools/ocaml/libs/xb/xb.ml
index 8404ddd8a682..165fd4a1edf4 100644
--- a/tools/ocaml/libs/xb/xb.ml
+++ b/tools/ocaml/libs/xb/xb.ml
@@ -45,7 +45,6 @@ type partial_buf = HaveHdr of Partial.pkt | NoHdr of int * bytes
 type t =
 {
 	backend: backend;
-	pkt_in: Packet.t Queue.t;
 	pkt_out: Packet.t Queue.t;
 	mutable partial_in: partial_buf;
 	mutable partial_out: string;
@@ -62,7 +61,6 @@ let reconnect t = match t.backend with
 		Xs_ring.close backend.mmap;
 		backend.eventchn_notify ();
 		(* Clear our old connection state *)
-		Queue.clear t.pkt_in;
 		Queue.clear t.pkt_out;
 		t.partial_in <- init_partial_in ();
 		t.partial_out <- ""
@@ -124,7 +122,6 @@ let output con =
 
 (* NB: can throw Reconnect *)
 let input con =
-	let newpacket = ref false in
 	let to_read =
 		match con.partial_in with
 		| HaveHdr partial_pkt -> Partial.to_complete partial_pkt
@@ -143,21 +140,19 @@ let input con =
 		if Partial.to_complete partial_pkt = 0 then (
 			let pkt = Packet.of_partialpkt partial_pkt in
 			con.partial_in <- init_partial_in ();
-			Queue.push pkt con.pkt_in;
-			newpacket := true
-		)
+			Some pkt
+		) else None
 	| NoHdr (i, buf)      ->
 		(* we complete the partial header *)
 		if sz > 0 then
 			Bytes.blit b 0 buf (Partial.header_size () - i) sz;
 		con.partial_in <- if sz = i then
-			HaveHdr (Partial.of_string (Bytes.to_string buf)) else NoHdr (i - sz, buf)
-	);
-	!newpacket
+			HaveHdr (Partial.of_string (Bytes.to_string buf)) else NoHdr (i - sz, buf);
+		None
+	)
 
 let newcon backend = {
 	backend = backend;
-	pkt_in = Queue.create ();
 	pkt_out = Queue.create ();
 	partial_in = init_partial_in ();
 	partial_out = "";
@@ -193,9 +188,6 @@ let has_output con = has_new_output con || has_old_output con
 
 let peek_output con = Queue.peek con.pkt_out
 
-let input_len con = Queue.length con.pkt_in
-let has_in_packet con = Queue.length con.pkt_in > 0
-let get_in_packet con = Queue.pop con.pkt_in
 let has_partial_input con = match con.partial_in with
 	| HaveHdr _ -> true
 	| NoHdr (n, _) -> n < Partial.header_size ()
diff --git a/tools/ocaml/libs/xb/xb.mli b/tools/ocaml/libs/xb/xb.mli
index 794e35bb343e..91c682162cea 100644
--- a/tools/ocaml/libs/xb/xb.mli
+++ b/tools/ocaml/libs/xb/xb.mli
@@ -77,7 +77,7 @@ val write_fd : backend_fd -> 'a -> string -> int -> int
 val write_mmap : backend_mmap -> 'a -> string -> int -> int
 val write : t -> string -> int -> int
 val output : t -> bool
-val input : t -> bool
+val input : t -> Packet.t option
 val newcon : backend -> t
 val open_fd : Unix.file_descr -> t
 val open_mmap : Xenmmap.mmap_interface -> (unit -> unit) -> t
@@ -89,10 +89,7 @@ val has_new_output : t -> bool
 val has_old_output : t -> bool
 val has_output : t -> bool
 val peek_output : t -> Packet.t
-val input_len : t -> int
-val has_in_packet : t -> bool
 val has_partial_input : t -> bool
-val get_in_packet : t -> Packet.t
 val has_more_input : t -> bool
 val is_selectable : t -> bool
 val get_fd : t -> Unix.file_descr
diff --git a/tools/ocaml/libs/xs/xsraw.ml b/tools/ocaml/libs/xs/xsraw.ml
index d982fb24dbb1..451f8b38dbcc 100644
--- a/tools/ocaml/libs/xs/xsraw.ml
+++ b/tools/ocaml/libs/xs/xsraw.ml
@@ -94,26 +94,18 @@ let pkt_send con =
 	done
 
 (* receive one packet - can sleep *)
-let pkt_recv con =
-	let workdone = ref false in
-	while not !workdone
-	do
-		workdone := Xb.input con.xb
-	done;
-	Xb.get_in_packet con.xb
+let rec pkt_recv con =
+	match Xb.input con.xb with
+	| Some packet -> packet
+	| None -> pkt_recv con
 
 let pkt_recv_timeout con timeout =
 	let fd = Xb.get_fd con.xb in
 	let r, _, _ = Unix.select [ fd ] [] [] timeout in
 	if r = [] then
 		true, None
-	else (
-		let workdone = Xb.input con.xb in
-		if workdone then
-			false, (Some (Xb.get_in_packet con.xb))
-		else
-			false, None
-	)
+	else
+		false, Xb.input con.xb
 
 let queue_watchevent con data =
 	let ls = split_string ~limit:2 '\000' data in
diff --git a/tools/ocaml/xenstored/connection.ml b/tools/ocaml/xenstored/connection.ml
index 38b47363a173..cc20e047d2b9 100644
--- a/tools/ocaml/xenstored/connection.ml
+++ b/tools/ocaml/xenstored/connection.ml
@@ -277,9 +277,7 @@ let get_transaction con tid =
 	Hashtbl.find con.transactions tid
 
 let do_input con = Xenbus.Xb.input con.xb
-let has_input con = Xenbus.Xb.has_in_packet con.xb
 let has_partial_input con = Xenbus.Xb.has_partial_input con.xb
-let pop_in con = Xenbus.Xb.get_in_packet con.xb
 let has_more_input con = Xenbus.Xb.has_more_input con.xb
 
 let has_output con = Xenbus.Xb.has_output con.xb
@@ -307,7 +305,7 @@ let is_bad con = match con.dom with None -> false | Some dom -> Domain.is_bad_do
    Restrictions below can be relaxed once xenstored learns to dump more
    of its live state in a safe way *)
 let has_extra_connection_data con =
-	let has_in = has_input con || has_partial_input con in
+	let has_in = has_partial_input con in
 	let has_out = has_output con in
 	let has_socket = con.dom = None in
 	let has_nondefault_perms = make_perm con.dom <> con.perm in
diff --git a/tools/ocaml/xenstored/process.ml b/tools/ocaml/xenstored/process.ml
index 6a3435c265d3..2d67456a2aa0 100644
--- a/tools/ocaml/xenstored/process.ml
+++ b/tools/ocaml/xenstored/process.ml
@@ -195,10 +195,9 @@ let parse_live_update args =
 			| _ when Unix.gettimeofday () < t.deadline -> false
 			| l ->
 				warn "timeout reached: have to wait, migrate or shutdown %d domains:" (List.length l);
-				let msgs = List.rev_map (fun con -> Printf.sprintf "%s: %d tx, in: %b, out: %b, perm: %s"
+				let msgs = List.rev_map (fun con -> Printf.sprintf "%s: %d tx, out: %b, perm: %s"
 					(Connection.get_domstr con)
 					(Connection.number_of_transactions con)
-					(Connection.has_input con)
 					(Connection.has_output con)
 					(Connection.get_perm con |> Perms.Connection.to_string)
 					) l in
@@ -705,16 +704,17 @@ let do_input store cons doms con =
 			info "%s requests a reconnect" (Connection.get_domstr con);
 			History.reconnect con;
 			info "%s reconnection complete" (Connection.get_domstr con);
-			false
+			None
 		| Failure exp ->
 			error "caught exception %s" exp;
 			error "got a bad client %s" (sprintf "%-8s" (Connection.get_domstr con));
 			Connection.mark_as_bad con;
-			false
+			None
 	in
 
-	if newpacket then (
-		let packet = Connection.pop_in con in
+	match newpacket with
+	| None -> ()
+	| Some packet ->
 		let tid, rid, ty, data = Xenbus.Xb.Packet.unpack packet in
 		let req = {Packet.tid=tid; Packet.rid=rid; Packet.ty=ty; Packet.data=data} in
 
@@ -724,8 +724,7 @@ let do_input store cons doms con =
 		         (Xenbus.Xb.Op.to_string ty) (sanitize_data data); *)
 		process_packet ~store ~cons ~doms ~con ~req;
 		write_access_log ~ty ~tid ~con:(Connection.get_domstr con) ~data;
-		Connection.incr_ops con;
-	)
+		Connection.incr_ops con
 
 let do_output _store _cons _doms con =
 	if Connection.has_output con then (