[PATCH v2] pasta: make it possible to disable socket splicing

[PATCH v2] pasta: make it possible to disable socket splicing

[Jon Maloy]

During testing it is sometimes useful to force traffic which would
normally be forwared by socket splicing through the tap interface.

In this commit, we add a command switch enabling such funtionality
for inbound local traffic.

For outbound local traffic this is much trickier, if even possible,
so leave that for a later commit.

Suggested-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Jon Maloy <jmaloy@redhat.com>

---
v2: Some minor changes based on feedback from PASST team
---
 conf.c  | 5 +++++
 fwd.c   | 2 +-
 passt.h | 2 ++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/conf.c b/conf.c
index 5107549..fe6fa04 100644
--- a/conf.c
+++ b/conf.c
@@ -846,6 +846,7 @@ 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 inbound 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"
@@ -1274,6 +1275,7 @@ 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' },
@@ -1701,6 +1703,9 @@ 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 72c7f72..45ad26a 100644
--- a/passt.h
+++ b/passt.h
@@ -225,6 +225,7 @@ struct ip6_ctx {
  * @no_dhcpv6:		Disable DHCPv6 server
  * @no_ndp:		Disable NDP handler altogether
  * @no_ra:		Disable router advertisements
+ * @no_splice:		Disable socket splicing for inbound traffic
  * @host_lo_to_ns_lo:	Map host loopback addresses to ns loopback addresses
  * @freebind:		Allow binding of non-local addresses for forwarding
  * @low_wmem:		Low probed net.core.wmem_max
@@ -286,6 +287,7 @@ struct ctx {
 	int no_dhcpv6;
 	int no_ndp;
 	int no_ra;
+	int no_splice;
 	int host_lo_to_ns_lo;
 	int freebind;
 
-- 
@@ -225,6 +225,7 @@ struct ip6_ctx {
  * @no_dhcpv6:		Disable DHCPv6 server
  * @no_ndp:		Disable NDP handler altogether
  * @no_ra:		Disable router advertisements
+ * @no_splice:		Disable socket splicing for inbound traffic
  * @host_lo_to_ns_lo:	Map host loopback addresses to ns loopback addresses
  * @freebind:		Allow binding of non-local addresses for forwarding
  * @low_wmem:		Low probed net.core.wmem_max
@@ -286,6 +287,7 @@ struct ctx {
 	int no_dhcpv6;
 	int no_ndp;
 	int no_ra;
+	int no_splice;
 	int host_lo_to_ns_lo;
 	int freebind;
 
-- 
2.45.2

Re: [PATCH v2] pasta: make it possible to disable socket splicing

[Stefano Brivio]

On Fri, 29 Nov 2024 17:49:46 -0500
Jon Maloy <jmaloy@redhat.com> wrote:

> During testing it is sometimes useful to force traffic which would
> normally be forwared by socket splicing through the tap interface.
> 
> In this commit, we add a command switch enabling such funtionality
> for inbound local traffic.
> 
> For outbound local traffic this is much trickier, if even possible,
> so leave that for a later commit.
> 
> Suggested-by: David Gibson <david@gibson.dropbear.id.au>
> Signed-off-by: Jon Maloy <jmaloy@redhat.com>
> 
> ---
> v2: Some minor changes based on feedback from PASST team
> ---
>  conf.c  | 5 +++++
>  fwd.c   | 2 +-
>  passt.h | 2 ++
>  3 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/conf.c b/conf.c
> index 5107549..fe6fa04 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -846,6 +846,7 @@ 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 inbound socket splicing\n"

I think this really needs an update to the man page as David mentioned.

We don't have any undocumented option (as far as I know!) and I don't
think it would be a particularly good idea to start now...

-- 
Stefano