Re: [PATCH 11/11] tcp_splice: Simplify selection of socket and pipe sides in socket handler

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

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On Fri, Nov 03, 2023 at 05:21:12PM +0100, Stefano Brivio wrote:
> On Thu, 12 Oct 2023 12:51:14 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > tcp_splice_sock_handler() uses the tcp_splice_dir() helper to select
> > which of the socket, pipe and counter fields to use depending on which
> > side of the connection the socket event is coming from.
> > 
> > Now that we are using arrays for the two sides, rather than separate named
> > fields, we can instead just use a variable indicating the side and use
> > that to index the arrays whever we need a particular side's field.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  tcp_splice.c | 81 ++++++++++++++--------------------------------------
> >  1 file changed, 22 insertions(+), 59 deletions(-)
> > 
> > diff --git a/tcp_splice.c b/tcp_splice.c
> > index 239f6d2..822d15a 100644
> > --- a/tcp_splice.c
> > +++ b/tcp_splice.c
> > @@ -438,29 +438,6 @@ static int tcp_splice_new(const struct ctx *c, struct tcp_splice_conn *conn,
> >  	return tcp_splice_connect(c, conn, s, port);
> >  }
> >  
> > -/**
> > - * tcp_splice_dir() - Set sockets/pipe pointers reflecting flow direction
> > - * @conn:	Connection pointers
> > - * @ref_sock:	Socket returned as reference from epoll
> > - * @reverse:	Reverse direction: @ref_sock is used as destination
> > - * @from:	Destination socket pointer to set
> > - * @to:		Source socket pointer to set
> > - * @pipes:	Pipe set, assigned on return
> > - */
> > -static void tcp_splice_dir(struct tcp_splice_conn *conn, int ref_sock,
> > -			   int reverse, int *from, int *to, int **pipes)
> > -{
> > -	if (!reverse) {
> > -		*from = ref_sock;
> > -		*to   = (*from == conn->s[0]) ? conn->s[1] : conn->s[0];
> > -	} else {
> > -		*to   = ref_sock;
> > -		*from = (*to   == conn->s[0]) ? conn->s[1] : conn->s[0];
> > -	}
> > -
> > -	*pipes = *from == conn->s[0] ? conn->pipe[0] : conn->pipe[1];
> > -}
> > -
> >  /**
> >   * tcp_splice_conn_from_sock() - Attempt to init state for a spliced connection
> >   * @c:		Execution context
> > @@ -521,8 +498,7 @@ void tcp_splice_sock_handler(struct ctx *c, struct tcp_splice_conn *conn,
> >  			     int s, uint32_t events)
> >  {
> >  	uint8_t lowat_set_flag, lowat_act_flag;
> > -	int from, to, *pipes, eof, never_read;
> > -	uint32_t *seq_read, *seq_write;
> > +	int fromside, eof, never_read;
> >  
> >  	if (conn->events == SPLICE_CLOSED)
> >  		return;
> > @@ -538,14 +514,15 @@ void tcp_splice_sock_handler(struct ctx *c, struct tcp_splice_conn *conn,
> >  	}
> >  
> >  	if (events & EPOLLOUT) {
> > -		if (s == conn->s[0])
> > +		if (s == conn->s[0]) {
> >  			conn_event(c, conn, ~OUT_WAIT_0);
> > -		else
> > +			fromside = 1;
> > +		} else {
> >  			conn_event(c, conn, ~OUT_WAIT_1);
> > -
> > -		tcp_splice_dir(conn, s, 1, &from, &to, &pipes);
> > +			fromside = 0;
> > +		}
> >  	} else {
> > -		tcp_splice_dir(conn, s, 0, &from, &to, &pipes);
> > +		fromside = s == conn->s[0] ? 0 : 1;
> >  	}
> >  
> >  	if (events & EPOLLRDHUP) {
> > @@ -566,24 +543,16 @@ swap:
> >  	eof = 0;
> >  	never_read = 1;
> >  
> > -	if (from == conn->s[0]) {
> > -		seq_read = &conn->read[0];
> > -		seq_write = &conn->written[0];
> > -		lowat_set_flag = RCVLOWAT_SET_0;
> > -		lowat_act_flag = RCVLOWAT_ACT_0;
> > -	} else {
> > -		seq_read = &conn->read[1];
> > -		seq_write = &conn->written[1];
> > -		lowat_set_flag = RCVLOWAT_SET_1;
> > -		lowat_act_flag = RCVLOWAT_ACT_1;
> > -	}
> > +	lowat_set_flag = fromside == 0 ? RCVLOWAT_SET_0 : RCVLOWAT_SET_1;
> > +	lowat_act_flag = fromside == 0 ? RCVLOWAT_ACT_0 : RCVLOWAT_ACT_1;
> >  
> >  	while (1) {
> >  		ssize_t readlen, to_write = 0, written;
> >  		int more = 0;
> >  
> >  retry:
> > -		readlen = splice(from, NULL, pipes[1], NULL, c->tcp.pipe_size,
> > +		readlen = splice(conn->s[fromside], NULL,
> > +				 conn->pipe[fromside][1], NULL, c->tcp.pipe_size,
> >  				 SPLICE_F_MOVE | SPLICE_F_NONBLOCK);
> >  		trace("TCP (spliced): %li from read-side call", readlen);
> >  		if (readlen < 0) {
> > @@ -608,7 +577,8 @@ retry:
> >  		}
> >  
> >  eintr:
> > -		written = splice(pipes[0], NULL, to, NULL, to_write,
> > +		written = splice(conn->pipe[fromside][0], NULL,
> > +				 conn->s[!fromside], NULL, to_write,
> >  				 SPLICE_F_MOVE | more | SPLICE_F_NONBLOCK);
> >  		trace("TCP (spliced): %li from write-side call (passed %lu)",
> >  		      written, to_write);
> > @@ -622,8 +592,8 @@ eintr:
> >  			    readlen > (long)c->tcp.pipe_size / 10) {
> >  				int lowat = c->tcp.pipe_size / 4;
> >  
> > -				setsockopt(from, SOL_SOCKET, SO_RCVLOWAT,
> > -					   &lowat, sizeof(lowat));
> > +				setsockopt(conn->s[fromside], SOL_SOCKET,
> > +					   SO_RCVLOWAT, &lowat, sizeof(lowat));
> >  
> >  				conn_flag(c, conn, lowat_set_flag);
> >  				conn_flag(c, conn, lowat_act_flag);
> > @@ -632,8 +602,8 @@ eintr:
> >  			break;
> >  		}
> >  
> > -		*seq_read  += readlen > 0 ? readlen : 0;
> > -		*seq_write += written > 0 ? written : 0;
> > +		conn->read[fromside]  += readlen > 0 ? readlen : 0;
> > +		conn->written[fromside] += written > 0 ? written : 0;
> 
> The extra whitespace had the function of making this look more
> "tabular", now you should add a further one (or drop it altogether
> depending on taste).

Ah, yes.  I've restored the alignment.


-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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