Re: [PATCH v9] pasta: Refactor pasta_ns_conf() to reduce nesting

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

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On Fri, Jul 10, 2026 at 07:53:09PM -0400, Jon Maloy wrote:
> We extract address and route configuration into two new helper
> functions pasta_conf_addrs() and pasta_conf_routes(), and replace
> the outer if (c->pasta_conf_ns) block with an early return. This
> reduces indentation and eliminates the goto labels.
> 
> There is no functional change in this commit.
> 
> Signed-off-by: Jon Maloy <jmaloy@redhat.com>

On the whole looks much nicer, but a couple of comments below.

> ---
> v7: -Removed redundant argument 'af' in nl_addr_set()
>     -Removed redundant label and 'goto's in pasta_ns_conf()
>     -Since I excluded addition of all LINKLOCAL addresses from host
>      address array in a previous commit I can now omit this test
>      in pasta_conf_addrs()  as suggested by David.
>     -Here is the example of agnostic usage of inany_prefix_len()
>      I referred to in a previous commit.
> 
> v8: -Do prefix_len conversion inside nl_addr_set() instead of in
>      the calling function.
>     -In nl_addr_set(), branch on inany_prefix_v4() return value instead
>      of inany_af() to avoid redundant AF check and potential static
>      checker false positives. (David)
>     -Swap branch order in pasta_conf_routes() for consistency with
>      pasta_conf_addrs(). (David)
>     -Defer investigation of pre-existing IFF_NOARP / DAD interaction
>      oddity noted by David.
> 
> v9: - Broke out as standalone from multi-addr series.
>     - Adapted to code conditions before the introduction of
>       the unified address type.
> ---
>  pasta.c | 226 +++++++++++++++++++++++++++++---------------------------
>  1 file changed, 117 insertions(+), 109 deletions(-)
> 
> diff --git a/pasta.c b/pasta.c
> index 4e7ee542..fa9a341e 100644
> --- a/pasta.c
> +++ b/pasta.c
> @@ -303,13 +303,72 @@ void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid,
>  		die_perror("Failed to join network namespace");
>  }
>  
> +/**
> + * pasta_conf_addrs() - Configure addresses for one address family in namespace
> + * @c:		Execution context
> + * @af:		Address family (AF_INET or AF_INET6)
> + * @ifi:	Host interface index for this address family
> + * @no_copy:	If true, set configured address; if false, copy from host
> + *
> + * Return: 0 on success, negative error code on failure
> + */
> +static int pasta_conf_addrs(struct ctx *c, sa_family_t af, int ifi,
> +			    bool no_copy)
> +{
> +	if (!ifi)
> +		return 0;
> +
> +	if (!no_copy)
> +		return nl_addr_dup(nl_sock, ifi, nl_sock_ns, c->pasta_ifi, af);
> +
> +	if (af == AF_INET) {

I think this also needs to check !IN4_IS_ADDR_UNSPECIFIED(&c->ip4.addr).

> +		return nl_addr_set(nl_sock_ns, c->pasta_ifi, AF_INET,
> +				   &c->ip4.addr, c->ip4.prefix_len);
> +	}
> +
> +	if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr))
> +		return nl_addr_set(nl_sock_ns, c->pasta_ifi, AF_INET6,
> +				   &c->ip6.addr, 64);
> +
> +	return 0;
> +}
> +
> +/**
> + * pasta_conf_routes() - Configure routes for one address family in namespace
> + * @c:		Execution context
> + * @af:		Address family (AF_INET or AF_INET6)
> + * @ifi:	Host interface index for this address family
> + * @no_copy:	If true, set default route; if false, copy routes from host
> + *
> + * Return: 0 on success, negative error code on failure
> + */
> +static int pasta_conf_routes(struct ctx *c, sa_family_t af, int ifi,
> +			     bool no_copy)
> +{
> +	const void *gw;
> +
> +	if (af == AF_INET)
> +		gw = &c->ip4.guest_gw;
> +	else
> +		gw = &c->ip6.guest_gw;
> +
> +	if (!ifi)
> +		return 0;
> +
> +	if (!no_copy)
> +		return nl_route_dup(nl_sock, ifi, nl_sock_ns, c->pasta_ifi, af);
> +
> +	return nl_route_set_def(nl_sock_ns, c->pasta_ifi, af, gw);
> +}
> +
>  /**
>   * pasta_ns_conf() - Set up loopback and tap interfaces in namespace as needed
>   * @c:		Execution context
>   */
>  void pasta_ns_conf(struct ctx *c)
>  {
> -	int rc = 0;
> +	unsigned int flags = IFF_UP;
> +	int rc;
>  
>  	rc = nl_link_set_flags(nl_sock_ns, 1 /* lo */, IFF_UP, IFF_UP);
>  	if (rc < 0)
> @@ -328,116 +387,65 @@ void pasta_ns_conf(struct ctx *c)
>  		die("Couldn't set MAC address in namespace: %s",
>  		    strerror_(-rc));
>  
> -	if (c->pasta_conf_ns) {
> -		unsigned int flags = IFF_UP;
> -
> -		if (c->mtu)
> -			nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu);
> -
> -		if (c->ifi6) /* Avoid duplicate address detection on link up */
> -			flags |= IFF_NOARP;
> -
> -		nl_link_set_flags(nl_sock_ns, c->pasta_ifi, flags, flags);
> -
> -		if (c->ifi4) {
> -			if (c->ip4.no_copy_addrs) {
> -				rc = nl_addr_set(nl_sock_ns, c->pasta_ifi,
> -						 AF_INET,
> -						 &c->ip4.addr,
> -						 c->ip4.prefix_len);
> -			} else {
> -				rc = nl_addr_dup(nl_sock, c->ifi4,
> -						 nl_sock_ns, c->pasta_ifi,
> -						 AF_INET);
> -			}
> -
> -			if (c->ifi4 == -1 && rc == -ENOTSUP) {
> -				warn("IPv4 not supported, disabling");
> -				c->ifi4 = 0;
> -				goto ipv4_done;
> -			}
> -
> -			if (rc < 0) {
> -				die("Couldn't set IPv4 address(es) in namespace: %s",
> -				    strerror_(-rc));
> -			}
> -
> -			if (c->ip4.no_copy_routes) {
> -				rc = nl_route_set_def(nl_sock_ns, c->pasta_ifi,
> -						      AF_INET,
> -						      &c->ip4.guest_gw);
> -			} else {
> -				rc = nl_route_dup(nl_sock, c->ifi4, nl_sock_ns,
> -						  c->pasta_ifi, AF_INET);
> -			}
> -
> -			if (rc < 0) {
> -				die("Couldn't set IPv4 route(s) in guest: %s",
> -				    strerror_(-rc));
> -			}
> -		}
> -ipv4_done:
> -
> -		if (c->ifi6) {
> -			rc = nl_addr_get_ll(nl_sock_ns, c->pasta_ifi,
> -					    &c->ip6.addr_ll_seen);
> -			if (rc < 0) {
> -				warn("Can't get LL address from namespace: %s",
> -				    strerror_(-rc));
> -			}
> -
> -			rc = nl_addr_set_ll_nodad(nl_sock_ns, c->pasta_ifi);
> -			if (rc < 0) {
> -				warn("Can't set nodad for LL in namespace: %s",
> -				    strerror_(-rc));
> -			}
> -
> -			/* We dodged DAD: re-enable neighbour solicitations */
> -			nl_link_set_flags(nl_sock_ns, c->pasta_ifi,
> -					  0, IFF_NOARP);
> -
> -			if (c->ip6.no_copy_addrs) {
> -				if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr)) {
> -					rc = nl_addr_set(nl_sock_ns,
> -							 c->pasta_ifi, AF_INET6,
> -							 &c->ip6.addr, 64);
> -				}
> -			} else {
> -				rc = nl_addr_dup(nl_sock, c->ifi6,
> -						 nl_sock_ns, c->pasta_ifi,
> -						 AF_INET6);
> -			}
> -
> -			if (rc < 0) {
> -				die("Couldn't set IPv6 address(es) in namespace: %s",
> -				    strerror_(-rc));
> -			}
> -
> -			if (c->ip6.no_copy_routes) {
> -				rc = nl_route_set_def(nl_sock_ns, c->pasta_ifi,
> -						      AF_INET6,
> -						      &c->ip6.guest_gw);
> -			} else {
> -				rc = nl_route_dup(nl_sock, c->ifi6,
> -						  nl_sock_ns, c->pasta_ifi,
> -						  AF_INET6);
> -			}
> -
> -			if (c->ifi6 == -1 && rc == -ENOTSUP) {
> -				warn("IPv6 not supported, disabling");
> -				c->ifi6 = 0;
> -				goto ipv6_done;
> -			}
> -
> -			if (rc < 0) {
> -				die("Couldn't set IPv6 route(s) in guest: %s",
> -				    strerror_(-rc));
> -			}
> -		}
> +	proto_update_l2_buf(c->guest_mac);
> +
> +	if (!c->pasta_conf_ns)
> +		return;
> +
> +	if (c->mtu)
> +		nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu);
> +
> +	if (c->ifi6) /* Avoid duplicate address detection on link up */
> +		flags |= IFF_NOARP;
> +
> +	nl_link_set_flags(nl_sock_ns, c->pasta_ifi, flags, flags);
> +

I realise it puts some of the nesting back in, but I think you still
need the if (c->ifi4) around the next chunk - a configuration with
only IPv6 configured is certainly supported.

> +	rc = pasta_conf_addrs(c, AF_INET, c->ifi4, c->ip4.no_copy_addrs);
> +	if (c->ifi4 == -1 && rc == -ENOTSUP) {
> +		warn("IPv4 not supported, disabling");
> +		c->ifi4 = 0;
> +	} else if (rc < 0) {
> +		die("Couldn't set IPv4 address(es) in namespace: %s",
> +		    strerror_(-rc));
> +	} else if (c->ifi4) {
> +		rc = pasta_conf_routes(c, AF_INET, c->ifi4,
> +				       c->ip4.no_copy_routes);
> +		if (rc < 0)
> +			die("Couldn't set IPv4 route(s) in guest: %s",
> +			    strerror_(-rc));
>  	}
> -ipv6_done:
>  
> -	proto_update_l2_buf(c->guest_mac);
> +	if (!c->ifi6)
> +		return;

For symmetry with IPv4 I'd put this chunk within the if, rather than
using an early return here.

> +
> +	rc = nl_addr_get_ll(nl_sock_ns, c->pasta_ifi,
> +			    &c->ip6.addr_ll_seen);
> +	if (rc < 0)
> +		warn("Can't get LL address from namespace: %s",
> +		     strerror_(-rc));
> +
> +	rc = nl_addr_set_ll_nodad(nl_sock_ns, c->pasta_ifi);
> +	if (rc < 0)
> +		warn("Can't set nodad for LL in namespace: %s",
> +		     strerror_(-rc));
> +
> +	/* We dodged DAD: re-enable neighbour solicitations */
> +	nl_link_set_flags(nl_sock_ns, c->pasta_ifi, 0, IFF_NOARP);
> +
> +	rc = pasta_conf_addrs(c, AF_INET6, c->ifi6, c->ip6.no_copy_addrs);
> +	if (c->ifi6 == -1 && rc == -ENOTSUP) {
> +		warn("IPv6 not supported, disabling");
> +		c->ifi6 = 0;
> +		return;
> +	} else if (rc < 0) {
> +		die("Couldn't set IPv6 address(es) in namespace: %s",
> +		    strerror_(-rc));
> +	}
> +
> +	rc = pasta_conf_routes(c, AF_INET6, c->ifi6, c->ip6.no_copy_routes);
> +	if (rc < 0)
> +		die("Couldn't set IPv6 route(s) in guest: %s",
> +		    strerror_(-rc));
>  }
>  
>  /**
> -- 
> 2.52.0
> 

-- 
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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