Re: [PATCH] pasta: make it possible to disable socket splicing

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 28 Nov 2024 19:45:32 -0500
Jon Maloy <jmaloy@redhat.com> wrote:

> During testing it is sometimes useful to force traffic which would
> normally be forwarded by socket splicing through the tap interface.
> 
> In this commit, we add a command switch making it possible to disable
> splicing for inbound local traffic.
> 
> For outbound local traffic this seems to be much trickier, so I leave
> that for a possible later commit.
> 
> Suggested-by: David Gibson <dgibson@redhat.com>

David's address is david@gibson.dropbear.id.au.

> Signed-off-by: Jon Maloy <jmaloy@redhat.com>
> ---
>  conf.c  | 5 +++++
>  fwd.c   | 2 +-
>  passt.h | 1 +
>  3 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/conf.c b/conf.c
> index eaa7d99..8d58652 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -890,6 +890,7 @@ static void usage(const char *name, FILE *f, int status)
>  		"  --no-ndp		Disable NDP responses\n"
>  		"  --no-dhcpv6		Disable DHCPv6 server\n"
>  		"  --no-ra		Disable router advertisements\n"
> +		"  --no-splice		Disable outbound socket splicing\n"
>  		"  --freebind		Bind to any address for forwarding\n"
>  		"  --no-map-gw		Don't map gateway address to host\n"
>  		"  -4, --ipv4-only	Enable IPv4 operation only\n"
> @@ -1319,6 +1320,7 @@ void conf(struct ctx *c, int argc, char **argv)
>  		{"no-dhcpv6",	no_argument,		&c->no_dhcpv6,	1 },
>  		{"no-ndp",	no_argument,		&c->no_ndp,	1 },
>  		{"no-ra",	no_argument,		&c->no_ra,	1 },
> +		{"no-splice",	no_argument,		&c->no_splice,	1 },
>  		{"freebind",	no_argument,		&c->freebind,	1 },
>  		{"no-map-gw",	no_argument,		&no_map_gw,	1 },
>  		{"ipv4-only",	no_argument,		NULL,		'4' },
> @@ -1756,6 +1758,9 @@ void conf(struct ctx *c, int argc, char **argv)
>  		}
>  	} while (name != -1);
>  
> +	if (c->mode == MODE_PASST)
> +		c->no_splice = 1;
> +
>  	if (c->mode == MODE_PASTA && !c->pasta_conf_ns) {
>  		if (copy_routes_opt)
>  			die("--no-copy-routes needs --config-net");
> diff --git a/fwd.c b/fwd.c
> index 0b7f8b1..2829cd2 100644
> --- a/fwd.c
> +++ b/fwd.c
> @@ -443,7 +443,7 @@ uint8_t fwd_nat_from_host(const struct ctx *c, uint8_t proto,
>  	else if (proto == IPPROTO_UDP)
>  		tgt->eport += c->udp.fwd_in.delta[tgt->eport];
>  
> -	if (c->mode == MODE_PASTA && inany_is_loopback(&ini->eaddr) &&
> +	if (!c->no_splice && inany_is_loopback(&ini->eaddr) &&
>  	    (proto == IPPROTO_TCP || proto == IPPROTO_UDP)) {
>  		/* spliceable */
>  
> diff --git a/passt.h b/passt.h
> index c038630..0271e7c 100644
> --- a/passt.h
> +++ b/passt.h
> @@ -291,6 +291,7 @@ struct ctx {
>  	int no_dhcpv6;
>  	int no_ndp;
>  	int no_ra;
> +	int no_splice;

This should also be documented in the comment to the struct.

-- 
Stefano