flow: Safer errno handling in flowside_connect() callers

flowside_connect() behaves much like connect(2) itself, returning -1 on
error with errno set to the error code.  One of the callers, in
udp_flow_sock(), uses the errno code with flow_dbg_perror() *after* it's
called epoll_del() and close() either of which could clobber errno.

Change flowside_connect() to use the more regular convention for internal
functions: return a negative errno code on error, rather than just -1.
Save it in the callers and use that rather than raw errno to print the
message.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

3 files changed, 9 insertions, 8 deletions

diff --git a/flow.c b/flow.c
index dd92bad..9882843 100644
--- a/flow.c
+++ b/flow.c
@@ -259,7 +259,7 @@ int flowside_sock_l4(const struct ctx *c, enum epoll_type type, uint8_t pif,
  *
  * Connect @s to the endpoint address and port from @tgt.
  *
- * Return: 0 on success, negative on error
+ * Return: 0 on success, negative error code on error
  */
 int flowside_connect(const struct ctx *c, int s,
 		     uint8_t pif, const struct flowside *tgt)
@@ -267,7 +267,9 @@ int flowside_connect(const struct ctx *c, int s,
 	union sockaddr_inany sa;
 
 	pif_sockaddr(c, &sa, pif, &tgt->eaddr, tgt->eport);
-	return connect(s, &sa.sa, socklen_inany(&sa));
+	if (connect(s, &sa.sa, socklen_inany(&sa)) < 0)
+		return -errno;
+	return 0;
 }
 
 /** flow_log__ - Log flow-related message, internal helper
diff --git a/tcp.c b/tcp.c
index 6fba865..8181364 100644
--- a/tcp.c
+++ b/tcp.c
@@ -3744,8 +3744,8 @@ static int tcp_flow_repair_connect(const struct ctx *c,
 
 	rc = flowside_connect(c, conn->sock, PIF_HOST, tgt);
 	if (rc) {
-		rc = -errno;
-		flow_perror(conn, "Failed to connect migrated socket");
+		flow_err(conn, "Failed to connect migrated socket: %s",
+			 strerror_(-rc));
 		return rc;
 	}
 
diff --git a/udp_flow.c b/udp_flow.c
index 35417bc..6edfa65 100644
--- a/udp_flow.c
+++ b/udp_flow.c
@@ -88,13 +88,12 @@ static int udp_flow_sock(const struct ctx *c,
 		return rc;
 	}
 
-	if (flowside_connect(c, s, pif, side) < 0) {
-		rc = -errno;
-
+	if ((rc = flowside_connect(c, s, pif, side)) < 0) {
 		epoll_del(flow_epollfd(&uflow->f), s);
 		close(s);
 
-		flow_dbg_perror(uflow, "Couldn't connect flow socket");
+		flow_dbg(uflow, "Couldn't connect flow socket: %s",
+			 strerror_(-rc));
 		return rc;
 	}
 	uflow->s[sidei] = s;