flow, udp: Fix errno handling in udp_flow_sock()

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.

Fix that by moving the debug message earlier: there's no reason it has to
wait until the epoll_del() and close().

While we're at it, adjust the comment on flowside_connect() to clarify
that it sets errno (rather than, say, returning an error code).

Suggested-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

2 files changed, 2 insertions, 2 deletions

diff --git a/flow.c b/flow.c
index b296339..85ac630 100644
--- a/flow.c
+++ b/flow.c
@@ -258,7 +258,7 @@ 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 on error (setting errno)
  */
 int flowside_connect(const struct ctx *c, int s,
 		     uint8_t pif, const struct flowside *tgt)
diff --git a/udp_flow.c b/udp_flow.c
index 35417bc..31e2f8a 100644
--- a/udp_flow.c
+++ b/udp_flow.c
@@ -90,11 +90,11 @@ static int udp_flow_sock(const struct ctx *c,
 
 	if (flowside_connect(c, s, pif, side) < 0) {
 		rc = -errno;
+		flow_dbg_perror(uflow, "Couldn't connect flow socket");
 
 		epoll_del(flow_epollfd(&uflow->f), s);
 		close(s);
 
-		flow_dbg_perror(uflow, "Couldn't connect flow socket");
 		return rc;
 	}
 	uflow->s[sidei] = s;