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Date:   Sat, 25 Mar 2017 21:59:47 -0400
From:   Vladislav Yasevich <vyasevich@...il.com>
To:     netdev@...r.kernel.org
Cc:     Vladislav Yasevich <vyasevic@...hat.com>
Subject: [PATCH net-next] rtnl: Add support for netdev event to link messages

RTNL currently generates notifications on some netdev notifier events.
However, user space has no idea what changed.  All it sees is the
data and has to infer what has changed.  For some events that is not
possible.

This patch adds a new field to RTM_NEWLINK message called IFLA_EVENT
that would have an encoding of the which event triggered this
notification.  Currectly, only 2 events (NETDEV_NOTIFY_PEERS and
NETDEV_MTUCHANGED) are supported.  These events could be interesting
in the virt space to trigger additional configuration commands to VMs.
Other events of interest may be added later.

Signed-off-by: Vladislav Yasevich <vyasevic@...hat.com>
---
 include/linux/rtnetlink.h    |  3 ++-
 include/uapi/linux/if_link.h |  7 ++++++
 net/core/dev.c               |  2 +-
 net/core/rtnetlink.c         | 51 ++++++++++++++++++++++++++++++++++++--------
 4 files changed, 52 insertions(+), 11 deletions(-)

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index 57e5484..0459018 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -18,7 +18,8 @@ extern int rtnl_put_cacheinfo(struct sk_buff *skb, struct dst_entry *dst,
 
 void rtmsg_ifinfo(int type, struct net_device *dev, unsigned change, gfp_t flags);
 struct sk_buff *rtmsg_ifinfo_build_skb(int type, struct net_device *dev,
-				       unsigned change, gfp_t flags);
+				       unsigned change, unsigned long event,
+				       gfp_t flags);
 void rtmsg_ifinfo_send(struct sk_buff *skb, struct net_device *dev,
 		       gfp_t flags);
 
diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index 320fc1e..8164d56 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -157,6 +157,7 @@ enum {
 	IFLA_GSO_MAX_SIZE,
 	IFLA_PAD,
 	IFLA_XDP,
+	IFLA_EVENT,
 	__IFLA_MAX
 };
 
@@ -890,6 +891,12 @@ enum {
 	__IFLA_XDP_MAX,
 };
 
+enum {
+	IFLA_EVENT_UNSPEC,
+	IFLA_EVENT_CHANGE_MTU,
+	IFLA_EVENT_NOTIFY_PEERS,
+};
+
 #define IFLA_XDP_MAX (__IFLA_XDP_MAX - 1)
 
 #endif /* _UAPI_LINUX_IF_LINK_H */
diff --git a/net/core/dev.c b/net/core/dev.c
index ef9fe60e..7efb417 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6840,7 +6840,7 @@ static void rollback_registered_many(struct list_head *head)
 
 		if (!dev->rtnl_link_ops ||
 		    dev->rtnl_link_state == RTNL_LINK_INITIALIZED)
-			skb = rtmsg_ifinfo_build_skb(RTM_DELLINK, dev, ~0U,
+			skb = rtmsg_ifinfo_build_skb(RTM_DELLINK, dev, ~0U, 0,
 						     GFP_KERNEL);
 
 		/*
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 9c3947a..63f5854 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -944,6 +944,7 @@ static noinline size_t if_nlmsg_size(const struct net_device *dev,
 	       + nla_total_size(MAX_PHYS_ITEM_ID_LEN) /* IFLA_PHYS_SWITCH_ID */
 	       + nla_total_size(IFNAMSIZ) /* IFLA_PHYS_PORT_NAME */
 	       + rtnl_xdp_size(dev) /* IFLA_XDP */
+	       + nla_total_size(4)  /* IFLA_EVENT */
 	       + nla_total_size(1); /* IFLA_PROTO_DOWN */
 
 }
@@ -1276,9 +1277,28 @@ static int rtnl_xdp_fill(struct sk_buff *skb, struct net_device *dev)
 	return err;
 }
 
+static int rtnl_fill_link_event(struct sk_buff *skb, unsigned long event)
+{
+	u32 rtnl_event;
+
+	switch (event) {
+	case NETDEV_NOTIFY_PEERS:
+		rtnl_event = IFLA_EVENT_NOTIFY_PEERS;
+		break;
+	case NETDEV_CHANGEMTU:
+		rtnl_event = IFLA_EVENT_CHANGE_MTU;
+		break;
+	default:
+		return 0;
+	}
+
+	return nla_put_u32(skb, IFLA_EVENT, rtnl_event);
+}
+
 static int rtnl_fill_ifinfo(struct sk_buff *skb, struct net_device *dev,
 			    int type, u32 pid, u32 seq, u32 change,
-			    unsigned int flags, u32 ext_filter_mask)
+			    unsigned int flags, u32 ext_filter_mask,
+			    unsigned long event)
 {
 	struct ifinfomsg *ifm;
 	struct nlmsghdr *nlh;
@@ -1327,6 +1347,9 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb, struct net_device *dev,
 	    nla_put_u8(skb, IFLA_PROTO_DOWN, dev->proto_down))
 		goto nla_put_failure;
 
+	if (rtnl_fill_link_event(skb, event))
+		goto nla_put_failure;
+
 	if (rtnl_fill_link_ifmap(skb, dev))
 		goto nla_put_failure;
 
@@ -1461,6 +1484,7 @@ static const struct nla_policy ifla_policy[IFLA_MAX+1] = {
 	[IFLA_LINK_NETNSID]	= { .type = NLA_S32 },
 	[IFLA_PROTO_DOWN]	= { .type = NLA_U8 },
 	[IFLA_XDP]		= { .type = NLA_NESTED },
+	[IFLA_EVENT]		= { .type = NLA_U32 },
 };
 
 static const struct nla_policy ifla_info_policy[IFLA_INFO_MAX+1] = {
@@ -1619,7 +1643,7 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 					       NETLINK_CB(cb->skb).portid,
 					       cb->nlh->nlmsg_seq, 0,
 					       flags,
-					       ext_filter_mask);
+					       ext_filter_mask, 0);
 			/* If we ran out of room on the first message,
 			 * we're in trouble
 			 */
@@ -2710,7 +2734,7 @@ static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr* nlh)
 		return -ENOBUFS;
 
 	err = rtnl_fill_ifinfo(nskb, dev, RTM_NEWLINK, NETLINK_CB(skb).portid,
-			       nlh->nlmsg_seq, 0, 0, ext_filter_mask);
+			       nlh->nlmsg_seq, 0, 0, ext_filter_mask, 0);
 	if (err < 0) {
 		/* -EMSGSIZE implies BUG in if_nlmsg_size */
 		WARN_ON(err == -EMSGSIZE);
@@ -2782,7 +2806,8 @@ static int rtnl_dump_all(struct sk_buff *skb, struct netlink_callback *cb)
 }
 
 struct sk_buff *rtmsg_ifinfo_build_skb(int type, struct net_device *dev,
-				       unsigned int change, gfp_t flags)
+				       unsigned int change, 
+				       unsigned long event, gfp_t flags)
 {
 	struct net *net = dev_net(dev);
 	struct sk_buff *skb;
@@ -2793,7 +2818,7 @@ struct sk_buff *rtmsg_ifinfo_build_skb(int type, struct net_device *dev,
 	if (skb == NULL)
 		goto errout;
 
-	err = rtnl_fill_ifinfo(skb, dev, type, 0, 0, change, 0, 0);
+	err = rtnl_fill_ifinfo(skb, dev, type, 0, 0, change, 0, 0, event);
 	if (err < 0) {
 		/* -EMSGSIZE implies BUG in if_nlmsg_size() */
 		WARN_ON(err == -EMSGSIZE);
@@ -2814,18 +2839,25 @@ void rtmsg_ifinfo_send(struct sk_buff *skb, struct net_device *dev, gfp_t flags)
 	rtnl_notify(skb, net, 0, RTNLGRP_LINK, NULL, flags);
 }
 
-void rtmsg_ifinfo(int type, struct net_device *dev, unsigned int change,
-		  gfp_t flags)
+static void rtmsg_ifinfo_event(int type, struct net_device *dev,
+			       unsigned int change, unsigned long event,
+			       gfp_t flags)
 {
 	struct sk_buff *skb;
 
 	if (dev->reg_state != NETREG_REGISTERED)
 		return;
 
-	skb = rtmsg_ifinfo_build_skb(type, dev, change, flags);
+	skb = rtmsg_ifinfo_build_skb(type, dev, change, event, flags);
 	if (skb)
 		rtmsg_ifinfo_send(skb, dev, flags);
 }
+
+void rtmsg_ifinfo(int type, struct net_device *dev, unsigned int change,
+		  gfp_t flags)
+{
+	rtmsg_ifinfo_event(type, dev, change, 0, flags);
+}
 EXPORT_SYMBOL(rtmsg_ifinfo);
 
 static int nlmsg_populate_fdb_fill(struct sk_buff *skb,
@@ -4044,6 +4076,7 @@ static int rtnl_stats_dump(struct sk_buff *skb, struct netlink_callback *cb)
 	return skb->len;
 }
 
+
 /* Process one rtnetlink message. */
 
 static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
@@ -4131,7 +4164,7 @@ static int rtnetlink_event(struct notifier_block *this, unsigned long event, voi
 	case NETDEV_BONDING_INFO:
 		break;
 	default:
-		rtmsg_ifinfo(RTM_NEWLINK, dev, 0, GFP_KERNEL);
+		rtmsg_ifinfo_event(RTM_NEWLINK, dev, 0, event, GFP_KERNEL);
 		break;
 	}
 	return NOTIFY_DONE;
-- 
2.7.4

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