gprs_ns2_fr: Monitor the kernel net-device link state

We use the newly-introduced libmnl integration of libosmocore in order
to receive netlink events from the kernel on link state changes.

If one of "our" interfaces changed link state, we report this in the log
and also store it within the "bind".

Change-Id: I779556991bfc88b7751b2be17bb81c329cfb9e01

1 files changed, 125 insertions, 2 deletions

diff --git a/src/gb/gprs_ns2_fr.c b/src/gb/gprs_ns2_fr.c
index 47d3a5dd..3cf44ef5 100644
--- a/src/gb/gprs_ns2_fr.c
+++ b/src/gb/gprs_ns2_fr.c
@@ -50,8 +50,10 @@
 #include <osmocom/core/select.h>
 #include <osmocom/core/socket.h>
 #include <osmocom/core/talloc.h>
+#include <osmocom/core/mnl.h>
 #include <osmocom/gprs/gprs_ns2.h>
 
+#include "config.h"
 #include "common_vty.h"
 #include "gprs_ns2_internal.h"
 
@@ -81,6 +83,7 @@ struct priv_bind {
 	struct osmo_fd fd;
 	char netif[IF_NAMESIZE];
 	struct osmo_fr_link *link;
+	bool if_running;
 };
 
 struct priv_vc {
@@ -112,8 +115,8 @@ static void dump_vty(const struct gprs_ns2_vc_bind *bind, struct vty *vty, bool
 	priv = bind->priv;
 	fr_link = priv->link;
 
-	vty_out(vty, "FR bind: %s, role: %s%s", priv->netif,
-		osmo_fr_role_str(fr_link->role), VTY_NEWLINE);
+	vty_out(vty, "FR bind: %s, role: %s, link: %s%s", priv->netif,
+		osmo_fr_role_str(fr_link->role), priv->if_running ? "UP" : "DOWN", VTY_NEWLINE);
 
 	llist_for_each_entry(nsvc, &bind->nsvc, blist) {
 		vty_out(vty, "    NSVCI %05u: %s%s", nsvc->nsvci, gprs_ns2_ll_str(nsvc), VTY_NEWLINE);
@@ -334,6 +337,116 @@ static int open_socket(const char *ifname)
 	return fd;
 }
 
+#ifdef ENABLE_LIBMNL
+
+#include <osmocom/core/mnl.h>
+#include <linux/if.h>
+#include <linux/if_link.h>
+#include <linux/rtnetlink.h>
+
+#ifndef ARPHRD_FRAD
+#define ARPHRD_FRAD  770
+#endif
+
+/* validate the netlink attributes */
+static int data_attr_cb(const struct nlattr *attr, void *data)
+{
+	const struct nlattr **tb = data;
+	int type = mnl_attr_get_type(attr);
+
+	if (mnl_attr_type_valid(attr, IFLA_MAX) < 0)
+		return MNL_CB_OK;
+
+	switch (type) {
+	case IFLA_MTU:
+		if (mnl_attr_validate(attr, MNL_TYPE_U32) < 0)
+			return MNL_CB_ERROR;
+		break;
+	case IFLA_IFNAME:
+		if (mnl_attr_validate(attr, MNL_TYPE_STRING) < 0)
+			return MNL_CB_ERROR;
+		break;
+	}
+	tb[type] = attr;
+	return MNL_CB_OK;
+}
+
+/* find the bind for the netdev (if any) */
+static struct gprs_ns2_vc_bind *bind4netdev(struct gprs_ns2_inst *nsi, const char *ifname)
+{
+	struct gprs_ns2_vc_bind *bind;
+
+	llist_for_each_entry(bind, &nsi->binding, list) {
+		struct priv_bind *bpriv = bind->priv;
+		if (!strcmp(bpriv->netif, ifname))
+			return bind;
+	}
+
+	return NULL;
+}
+
+/* handle a single netlink message received via libmnl */
+static int linkmon_mnl_cb(const struct nlmsghdr *nlh, void *data)
+{
+	struct osmo_mnl *omnl = data;
+	struct gprs_ns2_vc_bind *bind;
+	struct nlattr *tb[IFLA_MAX+1] = {};
+	struct ifinfomsg *ifm = mnl_nlmsg_get_payload(nlh);
+	struct gprs_ns2_inst *nsi;
+	const char *ifname;
+	bool if_running;
+
+	OSMO_ASSERT(omnl);
+	OSMO_ASSERT(ifm);
+
+	nsi = omnl->priv;
+
+	if (ifm->ifi_type != ARPHRD_FRAD)
+		return MNL_CB_OK;
+
+	mnl_attr_parse(nlh, sizeof(*ifm), data_attr_cb, tb);
+
+	if (!tb[IFLA_IFNAME])
+		return MNL_CB_OK;
+	ifname = mnl_attr_get_str(tb[IFLA_IFNAME]);
+	if_running = !!(ifm->ifi_flags & IFF_RUNNING);
+
+	bind = bind4netdev(nsi, ifname);
+	if (bind) {
+		struct priv_bind *bpriv = bind->priv;
+		if (bpriv->if_running != if_running) {
+			/* update running state */
+			LOGP(DLNS, LOGL_NOTICE, "FR net-device '%s': Physical link state changed: %s\n",
+			     ifname, if_running ? "UP" : "DOWN");
+			bpriv->if_running = if_running;
+		}
+	}
+
+	return MNL_CB_OK;
+}
+
+/* trigger one initial dump of all link information */
+static void linkmon_initial_dump(struct osmo_mnl *omnl)
+{
+	char buf[MNL_SOCKET_BUFFER_SIZE];
+	struct nlmsghdr *nlh = mnl_nlmsg_put_header(buf);
+	struct rtgenmsg *rt;
+
+	nlh->nlmsg_type = RTM_GETLINK;
+	nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
+	nlh->nlmsg_seq = time(NULL);
+	rt = mnl_nlmsg_put_extra_header(nlh, sizeof(struct rtgenmsg));
+	rt->rtgen_family = AF_PACKET;
+
+	if (mnl_socket_sendto(omnl->mnls, nlh, nlh->nlmsg_len) < 0) {
+		LOGP(DLNS, LOGL_ERROR, "linkmon: Cannot send rtnetlink message: %s\n", strerror(errno));
+	}
+
+	/* the response[s] will be handled just like the events */
+}
+#endif /* LIBMNL */
+
+
 /*! Create a new bind for NS over FR.
  *  \param[in] nsi NS instance in which to create the bind
  *  \param[in] netif Network interface to bind to
@@ -401,6 +514,16 @@ int gprs_ns2_fr_bind(struct gprs_ns2_inst *nsi,
 	INIT_LLIST_HEAD(&bind->nsvc);
 	llist_add(&bind->list, &nsi->binding);
 
+#ifdef ENABLE_LIBMNL
+	if (!nsi->linkmon_mnl)
+		nsi->linkmon_mnl = osmo_mnl_init(nsi, NETLINK_ROUTE, RTMGRP_LINK, linkmon_mnl_cb, nsi);
+
+	/* we get a new full dump after every bind. which is a bit excessive. But that's just once
+	 * at start-up, so we can get away with it */
+	if (nsi->linkmon_mnl)
+		linkmon_initial_dump(nsi->linkmon_mnl);
+#endif
+
 	return rc;
 
 err_fd: