[PATCH iproute2-next 2/2] ipmaddr: read link-layer multicast addresses via netlink

[Yuyang Huang <yuyanghuang@google.com>]

"ip maddr show" gets the IPv4 and IPv6 entries from RTM_GETMULTICAST
dumps but still parses /proc/net/dev_mcast for the link-layer ones.
The kernel now also dumps the device multicast list (dev->mc) for
RTM_GETMULTICAST requests with ifa_family AF_PACKET, so use it for
those too.

The dump carries every column of /proc/net/dev_mcast: IFA_MULTICAST is
the address, IFA_MC_USERS the reference count and IFA_F_GLOBAL in
IFA_FLAGS the "static" column, set for entries added explicitly, e.g.
by "ip maddr add". The output does not change.

Older kernels reject the AF_PACKET dump with EOPNOTSUPP, in which case
/proc/net/dev_mcast is parsed as before.

Signed-off-by: Yuyang Huang <yuyanghuang@google.com>
---
 ip/ipmaddr.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/ip/ipmaddr.c b/ip/ipmaddr.c
index 95b703d2..2df520a3 100644
--- a/ip/ipmaddr.c
+++ b/ip/ipmaddr.c
@@ -261,6 +261,10 @@ static int accept_maddr(struct nlmsghdr *n, void *arg)
 	ma->addr.bitlen = ma->addr.bytelen << 3;
 	memcpy(ma->addr.data, RTA_DATA(tb[IFA_MULTICAST]), ma->addr.bytelen);
 	ma->users = rta_getattr_u32(tb[IFA_MC_USERS]);
+	/* IFA_F_GLOBAL is the "static" column of /proc/net/dev_mcast */
+	if (ifm->ifa_family == AF_PACKET && tb[IFA_FLAGS] &&
+	    (rta_getattr_u32(tb[IFA_FLAGS]) & IFA_F_GLOBAL))
+		ma->features = "static";
 	maddr_ins(&ctx->list, ma);
 
 	return 0;
@@ -388,8 +392,10 @@ static int multiaddr_list(int argc, char **argv)
 		}
 	}
 
-	if (!filter.family || filter.family == AF_PACKET)
-		read_dev_mcast(&list);
+	if (!filter.family || filter.family == AF_PACKET) {
+		if (read_maddr_netlink(AF_PACKET, &list) < 0)
+			read_dev_mcast(&list);
+	}
 	if (!filter.family || filter.family == AF_INET) {
 		if (read_maddr_netlink(AF_INET, &list) < 0)
 			read_igmp(&list);
-- 
2.56.0.455.g6c5a503b38-goog