Re: [PATCH v5] pasta: make it possible to disable socket splicing

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

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On Tue, Dec 10, 2024 at 01:36:45PM -0500, Jon Maloy 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>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> 
> ---
> v2: Some minor changes based on feedback from PASST team
> v3: More changes based on feedback from D. Gibson and S. Brivio
>     -Moved new option to pasta-only section
>     -Added description to man-page
> v4: -Changed test on (mode == PASST) to (mode != PASTA) as
>      suggested by Stefano Brivio.
> v5: -Updated text in man pages as suggested by Stefano Brivio.
> ---
>  conf.c  | 7 ++++++-
>  fwd.c   | 2 +-
>  passt.1 | 5 +++++
>  passt.h | 2 ++
>  4 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/conf.c b/conf.c
> index eaa7d99..97d8beb 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -977,7 +977,8 @@ pasta_opts:
>  		"			Don't copy all routes to namespace\n"
>  		"  --no-copy-addrs	DEPRECATED:\n"
>  		"			Don't copy all addresses to namespace\n"
> -		"  --ns-mac-addr ADDR	Set MAC address on tap interface\n");
> +		"  --ns-mac-addr ADDR	Set MAC address on tap interface\n"
> +		"  --no-splice		Disable inbound socket splicing\n");
>  
>  	exit(status);
>  }
> @@ -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_PASTA)
> +		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.1 b/passt.1
> index b2896a2..d9cd33e 100644
> --- a/passt.1
> +++ b/passt.1
> @@ -695,6 +695,11 @@ Configure MAC address \fIaddr\fR on the tap interface in the namespace.
>  
>  Default is to let the tap driver build a pseudorandom hardware address.
>  
> +.TP
> +.BR \-\-no-splice
> +Disable the bypass path for inbound, local traffic. See the section \fBHandling
> +of local traffic in pasta\fR in the \fBNOTES\fR for more details.
> +
>  .SH EXAMPLES
>  
>  .SS \fBpasta
> diff --git a/passt.h b/passt.h
> index c038630..0dd4efa 100644
> --- a/passt.h
> +++ b/passt.h
> @@ -229,6 +229,7 @@ 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
> @@ -291,6 +292,7 @@ struct ctx {
>  	int no_dhcpv6;
>  	int no_ndp;
>  	int no_ra;
> +	int no_splice;
>  	int host_lo_to_ns_lo;
>  	int freebind;
>  

-- 
David Gibson (he or they)	| 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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