From 8231ce54c3953186f07f9aaebfd6986a303005aa Mon Sep 17 00:00:00 2001
From: Stefano Brivio <sbrivio@redhat.com>
Date: Thu, 15 Aug 2024 00:01:53 +0200
Subject: [PATCH] netlink, pasta: Split MTU setting functionality out of
 nl_link_up()

As we'll use nl_link_up() for more than just bringing up devices, it
will become awkward to carry empty MTU values around whenever we call
it.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
---
 netlink.c | 37 ++++++++++++++++++++++++++-----------
 netlink.h |  3 ++-
 pasta.c   |  7 +++++--
 3 files changed, 33 insertions(+), 14 deletions(-)

diff --git a/netlink.c b/netlink.c
index e6a315e..e33765e 100644
--- a/netlink.c
+++ b/netlink.c
@@ -942,14 +942,14 @@ int nl_link_set_mac(int s, unsigned int ifi, const void *mac)
 }
 
 /**
- * nl_link_up() - Bring link up
+ * nl_link_set_mtu() - Set link MTU
  * @s:		Netlink socket
  * @ifi:	Interface index
- * @mtu:	If non-zero, set interface MTU
+ * @mtu:	Interface MTU
  *
  * Return: 0 on success, negative error code on failure
  */
-int nl_link_up(int s, unsigned int ifi, int mtu)
+int nl_link_set_mtu(int s, unsigned int ifi, int mtu)
 {
 	struct req_t {
 		struct nlmsghdr nlh;
@@ -959,17 +959,32 @@ int nl_link_up(int s, unsigned int ifi, int mtu)
 	} req = {
 		.ifm.ifi_family	  = AF_UNSPEC,
 		.ifm.ifi_index	  = ifi,
-		.ifm.ifi_flags	  = IFF_UP,
-		.ifm.ifi_change	  = IFF_UP,
 		.rta.rta_type	  = IFLA_MTU,
 		.rta.rta_len	  = RTA_LENGTH(sizeof(unsigned int)),
 		.mtu		  = mtu,
 	};
-	ssize_t len = sizeof(req);
 
-	if (!mtu)
-		/* Shorten request to drop MTU attribute */
-		len = offsetof(struct req_t, rta);
-
-	return nl_do(s, &req, RTM_NEWLINK, 0, len);
+	return nl_do(s, &req, RTM_NEWLINK, 0, sizeof(req));
+}
+
+/**
+ * nl_link_up() - Bring link up
+ * @s:		Netlink socket
+ * @ifi:	Interface index
+ *
+ * Return: 0 on success, negative error code on failure
+ */
+int nl_link_up(int s, unsigned int ifi)
+{
+	struct req_t {
+		struct nlmsghdr nlh;
+		struct ifinfomsg ifm;
+	} req = {
+		.ifm.ifi_family	  = AF_UNSPEC,
+		.ifm.ifi_index	  = ifi,
+		.ifm.ifi_flags	  = IFF_UP,
+		.ifm.ifi_change	  = IFF_UP,
+	};
+
+	return nl_do(s, &req, RTM_NEWLINK, 0, sizeof(req));
 }
diff --git a/netlink.h b/netlink.h
index 3a1f0de..87d27ae 100644
--- a/netlink.h
+++ b/netlink.h
@@ -23,6 +23,7 @@ int nl_addr_dup(int s_src, unsigned int ifi_src,
 		int s_dst, unsigned int ifi_dst, sa_family_t af);
 int nl_link_get_mac(int s, unsigned int ifi, void *mac);
 int nl_link_set_mac(int s, unsigned int ifi, const void *mac);
-int nl_link_up(int s, unsigned int ifi, int mtu);
+int nl_link_set_mtu(int s, unsigned int ifi, int mtu);
+int nl_link_up(int s, unsigned int ifi);
 
 #endif /* NETLINK_H */
diff --git a/pasta.c b/pasta.c
index 615ff7b..3a0652e 100644
--- a/pasta.c
+++ b/pasta.c
@@ -288,7 +288,7 @@ void pasta_ns_conf(struct ctx *c)
 {
 	int rc = 0;
 
-	rc = nl_link_up(nl_sock_ns, 1 /* lo */, 0);
+	rc = nl_link_up(nl_sock_ns, 1 /* lo */);
 	if (rc < 0)
 		die("Couldn't bring up loopback interface in namespace: %s",
 		    strerror(-rc));
@@ -303,7 +303,10 @@ void pasta_ns_conf(struct ctx *c)
 		    strerror(-rc));
 
 	if (c->pasta_conf_ns) {
-		nl_link_up(nl_sock_ns, c->pasta_ifi, c->mtu);
+		if (c->mtu != -1)
+			nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu);
+
+		nl_link_up(nl_sock_ns, c->pasta_ifi);
 
 		if (c->ifi4) {
 			if (c->ip4.no_copy_addrs) {