[PATCH 1/1] ipv6 addrconf: add IFA_F_NOPREFIXROUTE flag to suppress creation of IP6 routes

[Thomas Haller <thaller@redhat.com>]

When adding/modifying an IPv6 address, the userspace application needs
a way to suppress adding a prefix route. This is for example relevant
together with IFA_F_MANAGERTEMPADDR, where userspace creates autoconf
generated addresses, but depending on on-link, no route should for the
prefix should be added.

This flag will not be set as ifa_flags of the address, it is only
considered as parameter while adding/modifying an address.

Signed-off-by: Thomas Haller <thaller@redhat.com>
---
 Hi, how about this?

 The flag is only a parameter for the netlink command.
 This might be unexpected, because when adding an address,
 you won't see the flag in `ip -6 addr`.
 Still, I think, it is better to do it this way, because having
 an address with the NOPREFIXROUTE flag, does not mean, that
 there is no route for this prefix. It only means, that at the
 moment of setting the address, no route was added.

 The alternative would be, not to add a prefix route, when
 IFA_F_MANAGERTEMPADDR is set.

 Thomas

 include/uapi/linux/if_addr.h |  1 +
 net/ipv6/addrconf.c          | 19 +++++++++++++------
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/include/uapi/linux/if_addr.h b/include/uapi/linux/if_addr.h
index cfed10b..dea10a8 100644
--- a/include/uapi/linux/if_addr.h
+++ b/include/uapi/linux/if_addr.h
@@ -49,6 +49,7 @@ enum {
 #define IFA_F_TENTATIVE		0x40
 #define IFA_F_PERMANENT		0x80
 #define IFA_F_MANAGETEMPADDR	0x100
+#define IFA_F_NOPREFIXROUTE	0x200
 
 struct ifa_cacheinfo {
 	__u32	ifa_prefered;
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 6c16345..51bd757 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -2429,12 +2429,16 @@ static int inet6_addr_add(struct net *net, int ifindex,
 		prefered_lft = timeout;
 	}
 
-	ifp = ipv6_add_addr(idev, pfx, peer_pfx, plen, scope, ifa_flags,
+	ifp = ipv6_add_addr(idev, pfx, peer_pfx, plen, scope,
+			    ifa_flags & ~IFA_F_NOPREFIXROUTE,
 			    valid_lft, prefered_lft);
 
 	if (!IS_ERR(ifp)) {
-		addrconf_prefix_route(&ifp->addr, ifp->prefix_len, dev,
-				      expires, flags);
+		if (ifa_flags & IFA_F_NOPREFIXROUTE == 0) {
+			addrconf_prefix_route(&ifp->addr, ifp->prefix_len, dev,
+					      expires, flags);
+		}
+
 		/*
 		 * Note that section 3.1 of RFC 4429 indicates
 		 * that the Optimistic flag should not be set for
@@ -3662,8 +3666,10 @@ static int inet6_addr_modify(struct inet6_ifaddr *ifp, u32 ifa_flags,
 	if (!(ifp->flags&IFA_F_TENTATIVE))
 		ipv6_ifa_notify(0, ifp);
 
-	addrconf_prefix_route(&ifp->addr, ifp->prefix_len, ifp->idev->dev,
-			      expires, flags);
+	if (ifa_flags & IFA_F_NOPREFIXROUTE == 0) {
+		addrconf_prefix_route(&ifp->addr, ifp->prefix_len, ifp->idev->dev,
+				      expires, flags);
+	}
 
 	if (was_managetempaddr || ifp->flags & IFA_F_MANAGETEMPADDR) {
 		if (was_managetempaddr && !(ifp->flags & IFA_F_MANAGETEMPADDR))
@@ -3717,7 +3723,8 @@ inet6_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh)
 	ifa_flags = tb[IFA_FLAGS] ? nla_get_u32(tb[IFA_FLAGS]) : ifm->ifa_flags;
 
 	/* We ignore other flags so far. */
-	ifa_flags &= IFA_F_NODAD | IFA_F_HOMEADDRESS | IFA_F_MANAGETEMPADDR;
+	ifa_flags &= IFA_F_NODAD | IFA_F_HOMEADDRESS | IFA_F_MANAGETEMPADDR |
+		     IFA_F_NOPREFIXROUTE;
 
 	ifa = ipv6_get_ifaddr(net, pfx, dev, 1);
 	if (ifa == NULL) {
-- 
1.8.4.2