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

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

[Jon Maloy]

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>

---
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) {
+		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);
+
+	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;
+
+	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