rtnl: Introduce RT netlink sockets.

This patch adds a source module that implements RT netlink sockets
for the purpose of link monitoring.  Unfortunately the netlink API
offers no possibility for per-port notification.  Instead it
forces us to use a de-multiplexing pattern.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>

makefile

@@ -25,7 +25,7 @@ LDLIBS	= -lm -lrt $(EXTRA_LDFLAGS)
 PRG	= ptp4l pmc phc2sys hwstamp_ctl phc_ctl timemaster
 OBJ     = bmc.o clock.o clockadj.o clockcheck.o config.o fault.o \
  filter.o fsm.o hash.o linreg.o mave.o mmedian.o msg.o ntpshm.o nullf.o phc.o \
- pi.o port.o print.o ptp4l.o raw.o servo.o sk.o stats.o tlv.o \
+ pi.o port.o print.o ptp4l.o raw.o rtnl.o servo.o sk.o stats.o tlv.o \
  transport.o tsproc.o udp.o udp6.o uds.o util.o version.o
 
 OBJECTS	= $(OBJ) hwstamp_ctl.o phc2sys.o phc_ctl.o pmc.o pmc_common.o \

rtnl.c

@@ -0,0 +1,166 @@
+/**
+ * @file rtnl.c
+ * @note Copyright (C) 2012 Richard Cochran <richardcochran@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+#include <asm/types.h>
+#include <linux/netlink.h>
+#include <linux/rtnetlink.h>
+#include <net/if.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+#include "print.h"
+#include "rtnl.h"
+
+static int rtnl_len;
+static char *rtnl_buf;
+
+int rtnl_close(int fd)
+{
+	if (rtnl_buf) {
+		free(rtnl_buf);
+		rtnl_buf = NULL;
+		rtnl_len = 0;
+	}
+	return close(fd);
+}
+
+int rtnl_link_query(int fd)
+{
+	struct sockaddr_nl sa;
+	struct msghdr msg;
+	struct iovec iov;
+	int cnt;
+
+	struct {
+		struct nlmsghdr hdr;
+		struct rtgenmsg gen;
+	} __attribute__((packed)) request;
+
+	memset(&sa, 0, sizeof(sa));
+	sa.nl_family = AF_NETLINK;
+
+	memset(&request, 0, sizeof(request));
+	request.hdr.nlmsg_len = NLMSG_LENGTH(sizeof(request.gen));
+	request.hdr.nlmsg_type = RTM_GETLINK;
+	request.hdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
+	request.hdr.nlmsg_seq = 1;
+	request.hdr.nlmsg_pid = 0;
+	request.gen.rtgen_family = AF_UNSPEC;
+
+	iov.iov_base = &request;
+	iov.iov_len = sizeof(request);
+
+	memset(&msg, 0, sizeof(msg));
+	msg.msg_name = &sa;
+	msg.msg_namelen = sizeof(sa);
+	msg.msg_iov = &iov;
+	msg.msg_iovlen = 1;
+
+	cnt = sendmsg(fd, &msg, 0);
+	if (cnt < 0) {
+		pr_err("rtnl: sendmsg: %m");
+		return -1;
+	}
+	return 0;
+}
+
+int rtnl_link_status(int fd, rtnl_callback cb, void *ctx)
+{
+	int index, len;
+	struct iovec iov;
+	struct sockaddr_nl sa;
+	struct msghdr msg;
+	struct nlmsghdr *nh;
+	struct ifinfomsg *info = NULL;
+
+	if (!rtnl_buf) {
+		rtnl_len = 4096;
+		rtnl_buf = malloc(rtnl_len);
+		if (!rtnl_buf) {
+			pr_err("rtnl: low memory");
+			return -1;
+		}
+	}
+
+	iov.iov_base = rtnl_buf;
+	iov.iov_len = rtnl_len;
+	memset(&msg, 0, sizeof(msg));
+	msg.msg_name = &sa;
+	msg.msg_namelen = sizeof(sa);
+	msg.msg_iov = &iov;
+	msg.msg_iovlen = 1;
+
+	len = recvmsg(fd, &msg, MSG_PEEK | MSG_TRUNC);
+	if (len < 1) {
+		pr_err("rtnl: recvmsg: %m");
+		return -1;
+	}
+	if (len > rtnl_len) {
+		free(rtnl_buf);
+		rtnl_len = len;
+		rtnl_buf = malloc(len);
+		if (!rtnl_buf) {
+			pr_err("rtnl: failed to resize to %d bytes", len);
+			return -1;
+		}
+		iov.iov_base = rtnl_buf;
+		iov.iov_len = rtnl_len;
+	}
+
+	len = recvmsg(fd, &msg, 0);
+	if (len < 1) {
+		pr_err("rtnl: recvmsg: %m");
+		return -1;
+	}
+	nh = (struct nlmsghdr *) rtnl_buf;
+
+	for ( ; NLMSG_OK(nh, len); nh = NLMSG_NEXT(nh, len)) {
+		if (nh->nlmsg_type == RTM_NEWLINK) {
+			info = NLMSG_DATA(nh);
+			index = info->ifi_index;
+			pr_debug("interface index %d is %s", index,
+				 info->ifi_flags & IFF_RUNNING ? "up" : "down");
+			cb(ctx, index, info->ifi_flags & IFF_RUNNING ? 1 : 0);
+		}
+	}
+	return 0;
+}
+
+int rtnl_open(void)
+{
+	int fd;
+	struct sockaddr_nl sa;
+
+	memset(&sa, 0, sizeof(sa));
+	sa.nl_family = AF_NETLINK;
+	sa.nl_groups = RTMGRP_LINK;
+
+	fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
+	if (fd < 0) {
+		pr_err("failed to open netlink socket: %m");
+		return -1;
+	}
+	if (bind(fd, (struct sockaddr *) &sa, sizeof(sa))) {
+		pr_err("failed to bind netlink socket: %m");
+		return -1;
+	}
+	return fd;
+}

rtnl.h

@@ -0,0 +1,54 @@
+/**
+ * @file rtnl.h
+ * @brief Interface link status via RT netlink
+ * @note Copyright (C) 2012 Richard Cochran <richardcochran@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+#ifndef HAVE_RTNL_H
+#define HAVE_RTNL_H
+
+typedef void (*rtnl_callback)(void *ctx, int index, int linkup);
+
+/**
+ * Close a RT netlink socket.
+ * @param fd  A socket obtained via rtnl_open().
+ * @return    Zero on success, non-zero otherwise.
+ */
+int rtnl_close(int fd);
+
+/**
+ * Request the link status from the kernel.
+ * @param fd  A socket obtained via rtnl_open().
+ * @return    Zero on success, non-zero otherwise.
+ */
+int rtnl_link_query(int fd);
+
+/**
+ * Read kernel messages looking for a link up/down events.
+ * @param fd   Readable socket obtained via rtnl_open().
+ * @param cb   Callback function to be invoked on each event.
+ * @param ctx  Private context passed to the callback.
+ * @return     Zero on success, non-zero otherwise.
+ */
+int rtnl_link_status(int fd, rtnl_callback cb, void *ctx);
+
+/**
+ * Open a RT netlink socket for monitoring link state.
+ * @return    A valid socket, or -1 on error.
+ */
+int rtnl_open(void);
+
+#endif