[PATCH 10/16] tcp_splice: Improve error reporting on connect path

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

This makes a number of changes to improve error reporting while connecting
a new spliced socket:
 * We use flow_err() and similar functions so all messages include info
   on which specific flow was affected
 * We use strerror() to interpret raw error values
 * We now report errors on connection (at "trace" level, since this would
   allow spamming the logs)
 * We also look up and report some details on EPOLLERR events, which can
   include connection errors, since we use a non-blocking connect().  Again
   we use "trace" level since this can spam the logs.
 * Use the 'goto fail' idiom in tcp_splice_conn_from_sock to combine some
   common handling

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tcp_splice.c | 36 +++++++++++++++++++++++++++++-------
 1 file changed, 29 insertions(+), 7 deletions(-)

diff --git a/tcp_splice.c b/tcp_splice.c
index 30b4d58a..abd698d4 100644
--- a/tcp_splice.c
+++ b/tcp_splice.c
@@ -387,7 +387,7 @@ bool tcp_splice_conn_from_sock(const struct ctx *c,
 	in_port_t srcport, dstport = ref.port;
 	union inany_addr src;
 	sa_family_t af;
-	int s1;
+	int s1, rc;
 
 	ASSERT(c->mode == MODE_PASTA);
 
@@ -420,15 +420,25 @@ bool tcp_splice_conn_from_sock(const struct ctx *c,
 	}
 
 	if (s1 < 0) {
-		warn("Couldn't open connectable socket for splice (%d)", s1);
-		conn_flag(c, conn, CLOSING);
-		return true;
+		flow_err(conn,
+			 "Couldn't open connectable socket for splice: %s",
+			 strerror(-s1));
+		goto fail;
 	}
 
-	if (tcp_splice_connect(c, conn, s1, dstport))
-		conn_flag(c, conn, CLOSING);
+	if ((rc = tcp_splice_connect(c, conn, s1, dstport))) {
+		flow_trace(conn, "Couldn't connect socket for splice: %s",
+			   strerror(-rc));
+		goto fail;
+	}
 
 	return true;
+
+fail:
+	/* This is *supposed* to be a spliced connection, but something went
+	 * wrong */
+	conn_flag(c, conn, CLOSING);
+	return true;
 }
 
 /**
@@ -452,8 +462,20 @@ void tcp_splice_sock_handler(struct ctx *c, union epoll_ref ref,
 	if (conn->events == SPLICE_CLOSED)
 		return;
 
-	if (events & EPOLLERR)
+	if (events & EPOLLERR) {
+		int err, rc;
+		socklen_t sl = sizeof(err);
+
+		rc = getsockopt(ref.fd, SOL_SOCKET, SO_ERROR, &err, &sl);
+		if (rc)
+			flow_err(conn, "Error retrieving SO_ERROR: %s",
+				 strerror(errno));
+		else
+			flow_trace(conn, "Error event on socket: %s",
+				   strerror(err));
+
 		goto close;
+	}
 
 	if (conn->events == SPLICE_CONNECT) {
 		if (!(events & EPOLLOUT))
-- 
@@ -387,7 +387,7 @@ bool tcp_splice_conn_from_sock(const struct ctx *c,
 	in_port_t srcport, dstport = ref.port;
 	union inany_addr src;
 	sa_family_t af;
-	int s1;
+	int s1, rc;
 
 	ASSERT(c->mode == MODE_PASTA);
 
@@ -420,15 +420,25 @@ bool tcp_splice_conn_from_sock(const struct ctx *c,
 	}
 
 	if (s1 < 0) {
-		warn("Couldn't open connectable socket for splice (%d)", s1);
-		conn_flag(c, conn, CLOSING);
-		return true;
+		flow_err(conn,
+			 "Couldn't open connectable socket for splice: %s",
+			 strerror(-s1));
+		goto fail;
 	}
 
-	if (tcp_splice_connect(c, conn, s1, dstport))
-		conn_flag(c, conn, CLOSING);
+	if ((rc = tcp_splice_connect(c, conn, s1, dstport))) {
+		flow_trace(conn, "Couldn't connect socket for splice: %s",
+			   strerror(-rc));
+		goto fail;
+	}
 
 	return true;
+
+fail:
+	/* This is *supposed* to be a spliced connection, but something went
+	 * wrong */
+	conn_flag(c, conn, CLOSING);
+	return true;
 }
 
 /**
@@ -452,8 +462,20 @@ void tcp_splice_sock_handler(struct ctx *c, union epoll_ref ref,
 	if (conn->events == SPLICE_CLOSED)
 		return;
 
-	if (events & EPOLLERR)
+	if (events & EPOLLERR) {
+		int err, rc;
+		socklen_t sl = sizeof(err);
+
+		rc = getsockopt(ref.fd, SOL_SOCKET, SO_ERROR, &err, &sl);
+		if (rc)
+			flow_err(conn, "Error retrieving SO_ERROR: %s",
+				 strerror(errno));
+		else
+			flow_trace(conn, "Error event on socket: %s",
+				   strerror(err));
+
 		goto close;
+	}
 
 	if (conn->events == SPLICE_CONNECT) {
 		if (!(events & EPOLLOUT))
-- 
2.43.0