[PATCH 1/3] migrate, tcp: More careful marshalling of mss parameter during migration

[David Gibson <david@gibson.dropbear.id.au>]

During migration we extract the limit on segment size using TCP_MAXSEG,
and set it on the other side with TCP_REPAIR_OPTIONS.  However, unlike most
32-bit values we transfer we transfer it in native endian, not network
endian.  This is not correct; add it to the list of endian fixups we make.

In addition, while MAXSEG will be 32-bits in practice, and is given as such
to TCP_REPAIR_OPTIONS, the TCP_MAXSEG sockopt treats it as an 'int'.  It's
not strictly safe to pass a uint32_t to a getsockopt() expecting an int,
although we'll get away with it on most (maybe all) platforms.  Correct
this as well.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tcp.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tcp.c b/tcp.c
index a4c840e6..163ddd60 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2847,14 +2847,17 @@ static int tcp_flow_dump_tinfo(const struct tcp_tap_conn *conn,
 static int tcp_flow_dump_mss(const struct tcp_tap_conn *conn,
 			     struct tcp_tap_transfer_ext *t)
 {
+	int val;
 	socklen_t sl = sizeof(t->mss);
 
-	if (getsockopt(conn->sock, SOL_TCP, TCP_MAXSEG, &t->mss, &sl)) {
+	if (getsockopt(conn->sock, SOL_TCP, TCP_MAXSEG, &val, &sl)) {
 		int rc = -errno;
 		flow_perror(conn, "Getting MSS");
 		return rc;
 	}
 
+	t->mss = (uint32_t)val;
+
 	return 0;
 }
 
@@ -3301,6 +3304,7 @@ int tcp_flow_migrate_source_ext(int fd, const struct tcp_tap_conn *conn)
 	t->sndq		= htonl(t->sndq);
 	t->notsent	= htonl(t->notsent);
 	t->rcvq		= htonl(t->rcvq);
+	t->mss		= htonl(t->mss);
 
 	t->snd_wl1	= htonl(t->snd_wl1);
 	t->snd_wnd	= htonl(t->snd_wnd);
@@ -3514,6 +3518,7 @@ int tcp_flow_migrate_target_ext(struct ctx *c, struct tcp_tap_conn *conn, int fd
 	t.sndq		= ntohl(t.sndq);
 	t.notsent	= ntohl(t.notsent);
 	t.rcvq		= ntohl(t.rcvq);
+	t.mss		= ntohl(t.mss);
 
 	t.snd_wl1	= ntohl(t.snd_wl1);
 	t.snd_wnd	= ntohl(t.snd_wnd);
-- 
@@ -2847,14 +2847,17 @@ static int tcp_flow_dump_tinfo(const struct tcp_tap_conn *conn,
 static int tcp_flow_dump_mss(const struct tcp_tap_conn *conn,
 			     struct tcp_tap_transfer_ext *t)
 {
+	int val;
 	socklen_t sl = sizeof(t->mss);
 
-	if (getsockopt(conn->sock, SOL_TCP, TCP_MAXSEG, &t->mss, &sl)) {
+	if (getsockopt(conn->sock, SOL_TCP, TCP_MAXSEG, &val, &sl)) {
 		int rc = -errno;
 		flow_perror(conn, "Getting MSS");
 		return rc;
 	}
 
+	t->mss = (uint32_t)val;
+
 	return 0;
 }
 
@@ -3301,6 +3304,7 @@ int tcp_flow_migrate_source_ext(int fd, const struct tcp_tap_conn *conn)
 	t->sndq		= htonl(t->sndq);
 	t->notsent	= htonl(t->notsent);
 	t->rcvq		= htonl(t->rcvq);
+	t->mss		= htonl(t->mss);
 
 	t->snd_wl1	= htonl(t->snd_wl1);
 	t->snd_wnd	= htonl(t->snd_wnd);
@@ -3514,6 +3518,7 @@ int tcp_flow_migrate_target_ext(struct ctx *c, struct tcp_tap_conn *conn, int fd
 	t.sndq		= ntohl(t.sndq);
 	t.notsent	= ntohl(t.notsent);
 	t.rcvq		= ntohl(t.rcvq);
+	t.mss		= ntohl(t.mss);
 
 	t.snd_wl1	= ntohl(t.snd_wl1);
 	t.snd_wnd	= ntohl(t.snd_wnd);
-- 
2.48.1