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

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 12 Oct 2023 12:51:13 +1100
David Gibson <david@gibson.dropbear.id.au> 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

> across the sides to reduce the duplication.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  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:

	if (conn->events & SPLICE_CONNECT) {
		close(conn->s[1]);
		conn->s[1] = -1;
	}

	close(conn->s[0]);
	conn->s[0] = -1;
	conn->read[side] = conn->written[side] = 0;

The handling for the SPLICE_ESTABLISHED case looks correct to me.

-- 
Stefano