flow: Clarify flow entry life cycle, introduce uniform logging

Our allocation scheme for flow entries means there are some
non-obvious constraints on when what things can be done with an entry.
Add a big doc comment explaining the life cycle.

In addition, make a FLOW_START() macro to mark one of the important
transitions.  This encourages correct usage, by making it natural to
only access the flow type specific structure after calling it.  It
also logs that a new flow has been created, which is useful for
debugging.

We also add logging when a flow's lifecycle ends.  This doesn't need a
new helper, because it can only happen either from flow_alloc_cancel()
or from the flow deferred handler.

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

1 files changed, 6 insertions, 5 deletions

diff --git a/tcp_splice.c b/tcp_splice.c
index 49585f2..2411a94 100644
--- a/tcp_splice.c
+++ b/tcp_splice.c
@@ -432,7 +432,7 @@ static int tcp_splice_new(const struct ctx *c, struct tcp_splice_conn *conn,
  * tcp_splice_conn_from_sock() - Attempt to init state for a spliced connection
  * @c:		Execution context
  * @ref:	epoll reference of listening socket
- * @conn:	connection structure to initialize
+ * @flow:	flow to initialise
  * @s:		Accepted socket
  * @sa:		Peer address of connection
  *
@@ -440,10 +440,10 @@ static int tcp_splice_new(const struct ctx *c, struct tcp_splice_conn *conn,
  * #syscalls:pasta setsockopt
  */
 bool tcp_splice_conn_from_sock(const struct ctx *c,
-			       union tcp_listen_epoll_ref ref,
-			       struct tcp_splice_conn *conn, int s,
-			       const union sockaddr_inany *sa)
+			       union tcp_listen_epoll_ref ref, union flow *flow,
+			       int s, const union sockaddr_inany *sa)
 {
+	struct tcp_splice_conn *conn;
 	union inany_addr aany;
 	in_port_t port;
 
@@ -453,7 +453,8 @@ bool tcp_splice_conn_from_sock(const struct ctx *c,
 	if (!inany_is_loopback(&aany))
 		return false;
 
-	conn->f.type = FLOW_TCP_SPLICE;
+	conn = FLOW_START(flow, FLOW_TCP_SPLICE, tcp_splice, 0);
+
 	conn->flags = inany_v4(&aany) ? 0 : SPLICE_V6;
 	conn->s[0] = s;
 	conn->s[1] = -1;