Re: [PATCH 10/11] tcp_splice: Exploit side symmetry in tcp_splice_destroy()

6 Nov 2023

On Mon, 6 Nov 2023 13:39:14 +1100
David Gibson  wrote:
...
On Fri, Nov 03, 2023 at 05:22:13PM +0100, Stefano Brivio wrote:
...
On Thu, 12 Oct 2023 12:51:13 +1100
David Gibson  wrote:
...
tcp_splice_destroy() has some close-to-duplicated logic handling closing of
the socket and ipies for each side of the connection.  We can use a loop  
                 ^^^^^ pipes
Oops, fixed.
...
...
across the sides to reduce the duplication.
Signed-off-by: David Gibson 
---
 tcp_splice.c | 32 ++++++++++++++------------------
 1 file changed, 14 insertions(+), 18 deletions(-)

diff --git a/tcp_splice.c b/tcp_splice.c
index 99ef8a4..239f6d2 100644
--- a/tcp_splice.c
+++ b/tcp_splice.c
@@ -258,30 +258,26 @@ void tcp_splice_conn_update(const struct ctx *c, struct tcp_splice_conn *new)
 void tcp_splice_destroy(struct ctx *c, union tcp_conn *conn_union)
 {
  struct tcp_splice_conn *conn = &conn_union->splice;
+	int side;
-	if (conn->events & SPLICE_ESTABLISHED) {
-		/* Flushing might need to block: don't recycle them. */
-		if (conn->pipe[0][0] != -1) {
-			close(conn->pipe[0][0]);
-			close(conn->pipe[0][1]);
-			conn->pipe[0][0] = conn->pipe[0][1] = -1;
+	for (side = 0; side < SIDES; side++) {
+		if (conn->events & SPLICE_ESTABLISHED) {
+			/* Flushing might need to block: don't recycle them. */
+			if (conn->pipe[side][0] != -1) {
+				close(conn->pipe[side][0]);
+				close(conn->pipe[side][1]);
+				conn->pipe[side][0] = conn->pipe[side][1] = -1;
+			}
      }
-		if (conn->pipe[1][0] != -1) {
-			close(conn->pipe[1][0]);
-			close(conn->pipe[1][1]);
-			conn->pipe[1][0] = conn->pipe[1][1] = -1;
+
+		if (side == 0 || conn->events & SPLICE_CONNECT) {
+			close(conn->s[side]);
+			conn->s[side] = -1;
      }
-	}
-	if (conn->events & SPLICE_CONNECT) {
-		close(conn->s[1]);
-		conn->s[1] = -1;
+		conn->read[side] = conn->written[side] = 0;
  }
-	close(conn->s[0]);
-	conn->s[0] = -1;
-	conn->read[0] = conn->written[0] = conn->read[1] = conn->written[1] = 0;
With this, on SPLICE_CONNECT, we would close the [0] side, but not the
[1] side. SPLICE_CONNECT means we already have an open socket for [1],
though. I think it should be:
[loop on sides]
if (side == 1 || conn->events & SPLICE_CONNECT) {
      	close(conn->s[side]);
      	conn->s[1] = -1;
      }
  }
and then we still need to unconditionally close conn->s[0]. Perhaps we could
take both parts outside of the loop:
Uh.. I think you're misreading.  In the updated code we have:
      if (side == 0 || conn->events & SPLICE_CONNECT) {
      	close(conn->s[side]);
      	conn->s[side] = -1;
      }
That's an OR, so we always close side 0, and we close side 1 iff we
have SPLICE_CONNECT, which matches what you're describing.
Gosh, yes, sorry, I read && for some reason.

-- 
Stefano

    