ifplugd: new applet by Maksym Kryzhanovskyy (xmaks AT email.cz)

 +3k code and 0.5k in messages. Most of the bloat due to compat :(

1 files changed, 810 insertions, 0 deletions

diff --git a/networking/ifplugd.c b/networking/ifplugd.c
new file mode 100644
index 000000000..5a389fdf9
--- /dev/null
+++ b/networking/ifplugd.c
@@ -0,0 +1,810 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * ifplugd for busybox
+ *
+ * Copyright (C) 2009
+ *
+ * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
+ */
+#include "libbb.h"
+
+#include <linux/if.h>
+#include <linux/ethtool.h>
+#include <net/ethernet.h>
+#include <linux/netlink.h>
+#include <linux/rtnetlink.h>
+#include <linux/sockios.h>
+#include <syslog.h>
+
+#define __user
+#include <linux/wireless.h>
+
+#define IFPLUGD_ENV_PREVIOUS "IFPLUGD_PREVIOUS"
+#define IFPLUGD_ENV_CURRENT "IFPLUGD_CURRENT"
+
+enum {
+	FLAG_NO_AUTO			= 1 <<  0, // -a, Do not enable interface automatically
+	FLAG_NO_DAEMON			= 1 <<  1, // -n, Do not daemonize
+	FLAG_NO_SYSLOG			= 1 <<  2, // -s, Do not use syslog, use stderr instead
+	FLAG_IGNORE_FAIL		= 1 <<  3, // -f, Ignore detection failure, retry instead (failure is treated as DOWN)
+	FLAG_IGNORE_FAIL_POSITIVE	= 1 <<  4, // -F, Ignore detection failure, retry instead (failure is treated as UP)
+	FLAG_IFACE			= 1 <<  5, // -i, Specify ethernet interface
+	FLAG_RUN			= 1 <<  6, // -r, Specify program to execute
+	FLAG_IGNORE_RETVAL		= 1 <<  7, // -I, Don't exit on nonzero return value of program executed
+	FLAG_POLL_TIME			= 1 <<  8, // -t, Specify poll time in seconds
+	FLAG_DELAY_UP			= 1 <<  9, // -u, Specify delay for configuring interface
+	FLAG_DELAY_DOWN			= 1 << 10, // -d, Specify delay for deconfiguring interface
+	FLAG_API_MODE			= 1 << 11, // -m, Force API mode (mii, priv, ethtool, wlan, auto)
+	FLAG_NO_STARTUP			= 1 << 12, // -p, Don't run script on daemon startup
+	FLAG_NO_SHUTDOWN		= 1 << 13, // -q, Don't run script on daemon quit
+	FLAG_INITIAL_DOWN		= 1 << 14, // -l, Run "down" script on startup if no cable is detected
+	FLAG_EXTRA_ARG			= 1 << 15, // -x, Specify an extra argument for action script
+	FLAG_MONITOR			= 1 << 16, // -M, Use interface monitoring
+#if ENABLE_FEATURE_PIDFILE
+	FLAG_KILL			= 1 << 17, // -k, Kill a running daemon
+#endif
+};
+#if ENABLE_FEATURE_PIDFILE
+# define OPTION_STR "+ansfFi:r:It:u:d:m:pqlx:Mk"
+#else
+# define OPTION_STR "+ansfFi:r:It:u:d:m:pqlx:M"
+#endif
+
+enum { // api mode
+	API_AUTO	= 'a',
+	API_ETHTOOL	= 'e',
+	API_MII		= 'm',
+	API_PRIVATE	= 'p',
+	API_WLAN	= 'w',
+	API_IFF		= 'i',
+};
+
+enum { // interface status
+	IFSTATUS_ERR = -1,
+	IFSTATUS_DOWN = 0,
+	IFSTATUS_UP = 1,
+};
+
+enum { // constant fds
+	ioctl_fd = 3,
+	netlink_fd = 4,
+};
+
+struct globals {
+	smallint iface_last_status;
+	smallint iface_exists;
+
+	/* Used in getopt32, must have sizeof == sizeof(int) */
+	unsigned poll_time;
+	unsigned delay_up;
+	unsigned delay_down;
+
+	const char *iface;
+	const char *api_mode;
+	const char *script_name;
+	const char *extra_arg;
+
+	smallint (*detect_link_func)(void);
+	smallint (*cached_detect_link_func)(void);
+};
+#define G (*ptr_to_globals)
+#define INIT_G() do { \
+	SET_PTR_TO_GLOBALS(xzalloc(sizeof(G))); \
+	G.iface_last_status = -1; \
+	G.iface_exists   = 1; \
+	G.poll_time      = 1; \
+	G.delay_down     = 5; \
+	G.iface          = "eth0"; \
+	G.api_mode       = "a"; \
+	G.script_name    = "/etc/ifplugd/ifplugd.action"; \
+} while (0)
+
+
+static int run_script(const char *action)
+{
+	pid_t pid;
+	int r;
+
+	bb_error_msg("executing '%s %s %s'", G.script_name, G.iface, action);
+
+#if 1
+	pid = vfork();
+	if (pid < 0) {
+		bb_perror_msg("fork");
+		return -1;
+	}
+
+	if (pid == 0) {
+		/* child */
+		execlp(G.script_name, G.script_name, G.iface, action, G.extra_arg, NULL);
+		bb_perror_msg_and_die("can't execute '%s'", G.script_name);
+	}
+
+	/* parent */
+	wait(&r);
+	r = WEXITSTATUS(r);
+
+	bb_error_msg("exit code: %u", r);
+	return (option_mask32 & FLAG_IGNORE_RETVAL) ? 0 : r;
+
+#else /* insanity */
+
+	struct fd_pair pipe_pair;
+	char buf[256];
+	int i = 0;
+
+	xpiped_pair(pipe_pair);
+
+	pid = vfork();
+	if (pid < 0) {
+		bb_perror_msg("fork");
+		return -1;
+	}
+
+	/* child */
+	if (pid == 0) {
+		xmove_fd(pipe_pair.wr, 1);
+		xdup2(1, 2);
+		if (pipe_pair.rd > 2)
+			close(pipe_pair.rd);
+
+		// umask(0022); // Set up a sane umask
+
+		execlp(G.script_name, G.script_name, G.iface, action, G.extra_arg, NULL);
+		_exit(EXIT_FAILURE);
+	}
+
+	/* parent */
+	close(pipe_pair.wr);
+
+	while (1) {
+		if (bb_got_signal && bb_got_signal != SIGCHLD) {
+			bb_error_msg("killing child");
+			kill(pid, SIGTERM);
+			bb_got_signal = 0;
+			break;
+		}
+
+		r = read(pipe_pair.rd, &buf[i], 1);
+
+		if (buf[i] == '\n' || i == sizeof(buf)-2 || r != 1) {
+			if (r == 1 && buf[i] != '\n')
+				i++;
+
+			buf[i] = '\0';
+
+			if (i > 0)
+				bb_error_msg("client: %s", buf);
+
+			i = 0;
+		} else {
+			i++;
+		}
+
+		if (r != 1)
+			break;
+	}
+
+	close(pipe_pair.rd);
+
+	wait(&r);
+
+	if (!WIFEXITED(r) || WEXITSTATUS(r) != 0) {
+		bb_error_msg("program execution failed, return value is %i",
+			WEXITSTATUS(r));
+		return option_mask32 & FLAG_IGNORE_RETVAL ? 0 : WEXITSTATUS(r);
+	}
+	bb_error_msg("program executed successfully");
+	return 0;
+#endif
+}
+
+static int network_ioctl(int request, void* data)
+{
+	return ioctl(ioctl_fd, request, data);
+}
+
+static void set_ifreq_to_ifname(struct ifreq *ifreq)
+{
+	memset(ifreq, 0, sizeof(struct ifreq));
+	strncpy(ifreq->ifr_name, G.iface, IFNAMSIZ);
+}
+
+static const char *strstatus(int status)
+{
+	if (status == IFSTATUS_ERR)
+		return "error";
+	return "down\0up" + (status * 5);
+}
+
+static void up_iface(void)
+{
+	struct ifreq ifrequest;
+
+	if (!G.iface_exists)
+		return;
+
+	set_ifreq_to_ifname(&ifrequest);
+	if (network_ioctl(SIOCGIFFLAGS, &ifrequest) < 0) {
+		bb_perror_msg("can't %cet interface flags", 'g');
+		G.iface_exists = 0;
+		return;
+	}
+
+	if (!(ifrequest.ifr_flags & IFF_UP)) {
+		ifrequest.ifr_flags |= IFF_UP;
+		/* Let user know we mess up with interface */
+		bb_error_msg("upping interface");
+		if (network_ioctl(SIOCSIFFLAGS, &ifrequest) < 0)
+			bb_perror_msg_and_die("can't %cet interface flags", 's');
+	}
+
+#if 0 /* why do we mess with IP addr? It's not our business */
+	if (network_ioctl(SIOCGIFADDR, &ifrequest) < 0) {
+		bb_error_msg("can't get interface address");
+	} else if (ifrequest.ifr_addr.sa_family != AF_INET) {
+		bb_perror_msg("The interface is not IP-based");
+	} else {
+		((struct sockaddr_in*)(&ifrequest.ifr_addr))->sin_addr.s_addr = INADDR_ANY;
+		if (network_ioctl(SIOCSIFADDR, &ifrequest) < 0)
+			bb_perror_msg("can't set interface address");
+	}
+	if (network_ioctl(SIOCGIFFLAGS, &ifrequest) < 0) {
+		bb_perror_msg("can't get interface flags");
+		return;
+	}
+#endif
+}
+
+static void maybe_up_new_iface(void)
+{
+	if (!(option_mask32 & FLAG_NO_AUTO))
+		up_iface();
+
+#if 0 /* bloat */
+	struct ifreq ifrequest;
+	struct ethtool_drvinfo driver_info;
+
+	set_ifreq_to_ifname(&ifrequest);
+	driver_info.cmd = ETHTOOL_GDRVINFO;
+	ifrequest.ifr_data = &driver_info;
+	if (network_ioctl(SIOCETHTOOL, &ifrequest) == 0) {
+		char buf[sizeof("/xx:xx:xx:xx:xx:xx")];
+
+		/* Get MAC */
+		buf[0] = '\0';
+		set_ifreq_to_ifname(&ifrequest);
+		if (network_ioctl(SIOCGIFHWADDR, &ifrequest) == 0) {
+			sprintf(buf, "/%02X:%02X:%02X:%02X:%02X:%02X",
+				(uint8_t)(ifrequest.ifr_hwaddr.sa_data[0]),
+				(uint8_t)(ifrequest.ifr_hwaddr.sa_data[1]),
+				(uint8_t)(ifrequest.ifr_hwaddr.sa_data[2]),
+				(uint8_t)(ifrequest.ifr_hwaddr.sa_data[3]),
+				(uint8_t)(ifrequest.ifr_hwaddr.sa_data[4]),
+				(uint8_t)(ifrequest.ifr_hwaddr.sa_data[5]));
+		}
+
+		bb_error_msg("Using interface %s%s with driver<%s> (version: %s)",
+			G.iface, buf, driver_info.driver, driver_info.version);
+	}
+#endif
+
+	G.cached_detect_link_func = NULL;
+}
+
+static smallint detect_link_mii(void)
+{
+	struct ifreq ifreq;
+
+	set_ifreq_to_ifname(&ifreq);
+
+	if (network_ioctl(SIOCGMIIPHY, &ifreq) < 0) {
+		bb_perror_msg("SIOCGMIIPHY failed");
+		return IFSTATUS_ERR;
+	}
+
+	((unsigned short*)&ifreq.ifr_data)[1] = 1;
+
+	if (network_ioctl(SIOCGMIIREG, &ifreq) < 0) {
+		bb_perror_msg("SIOCGMIIREG failed");
+		return IFSTATUS_ERR;
+	}
+
+	return (((unsigned short*)&ifreq.ifr_data)[3] & 0x0004) ?
+		IFSTATUS_UP : IFSTATUS_DOWN;
+}
+
+static smallint detect_link_priv(void)
+{
+	struct ifreq ifreq;
+
+	set_ifreq_to_ifname(&ifreq);
+
+	if (network_ioctl(SIOCDEVPRIVATE, &ifreq) < 0) {
+		bb_perror_msg("SIOCDEVPRIVATE failed");
+		return IFSTATUS_ERR;
+	}
+
+	((unsigned short*) &ifreq.ifr_data)[1] = 1;
+
+	if (network_ioctl(SIOCDEVPRIVATE+1, &ifreq) < 0) {
+		bb_perror_msg("SIOCDEVPRIVATE+1 failed");
+		return IFSTATUS_ERR;
+	}
+
+	return (((unsigned short*)&ifreq.ifr_data)[3] & 0x0004) ?
+		IFSTATUS_UP : IFSTATUS_DOWN;
+}
+
+static smallint detect_link_ethtool(void)
+{
+	struct ifreq ifreq;
+	struct ethtool_value edata;
+
+	set_ifreq_to_ifname(&ifreq);
+
+	edata.cmd = ETHTOOL_GLINK;
+	ifreq.ifr_data = &edata;
+
+	if (network_ioctl(SIOCETHTOOL, &ifreq) < 0) {
+		bb_perror_msg("ETHTOOL_GLINK failed");
+		return IFSTATUS_ERR;
+	}
+
+	return edata.data ? IFSTATUS_UP : IFSTATUS_DOWN;
+}
+
+static smallint detect_link_iff(void)
+{
+	struct ifreq ifreq;
+
+	set_ifreq_to_ifname(&ifreq);
+
+	if (network_ioctl(SIOCGIFFLAGS, &ifreq) < 0) {
+		bb_perror_msg("SIOCGIFFLAGS failed");
+		return IFSTATUS_ERR;
+	}
+
+	return (ifreq.ifr_flags & IFF_RUNNING) ? IFSTATUS_UP : IFSTATUS_DOWN;
+}
+
+static smallint detect_link_wlan(void)
+{
+	struct iwreq iwrequest;
+	uint8_t mac[ETH_ALEN];
+
+	memset(&iwrequest, 0, sizeof(struct iwreq));
+	strncpy(iwrequest.ifr_ifrn.ifrn_name, G.iface, IFNAMSIZ);
+
+	if (network_ioctl(SIOCGIWAP, &iwrequest) < 0) {
+		bb_perror_msg("SIOCGIWAP failed");
+		return IFSTATUS_ERR;
+	}
+
+	memcpy(mac, &(iwrequest.u.ap_addr.sa_data), ETH_ALEN);
+
+	if (mac[0] == 0xFF || mac[0] == 0x44 || mac[0] == 0x00) {
+		for (int i = 1; i < ETH_ALEN; ++i) {
+			if (mac[i] != mac[0])
+				return IFSTATUS_UP;
+		}
+		return IFSTATUS_DOWN;
+	}
+
+	return IFSTATUS_UP;
+}
+
+static smallint detect_link_auto(void)
+{
+	const char *method;
+	smallint iface_status;
+	smallint sv_logmode;
+
+	if (G.cached_detect_link_func) {
+		iface_status = G.cached_detect_link_func();
+		if (iface_status != IFSTATUS_ERR)
+			return iface_status;
+	}
+
+	sv_logmode = logmode;
+	logmode = LOGMODE_NONE;
+
+	iface_status = detect_link_ethtool();
+	if (iface_status != IFSTATUS_ERR) {
+		G.cached_detect_link_func = detect_link_ethtool;
+		method = "SIOCETHTOOL";
+ found_method:
+		logmode = sv_logmode;
+		bb_error_msg("using %s detection mode", method);
+		return iface_status;
+	}
+
+	iface_status = detect_link_mii();
+	if (iface_status != IFSTATUS_ERR) {
+		G.cached_detect_link_func = detect_link_mii;
+		method = "SIOCGMIIPHY";
+		goto found_method;
+	}
+
+	iface_status = detect_link_priv();
+	if (iface_status != IFSTATUS_ERR) {
+		G.cached_detect_link_func = detect_link_priv;
+		method = "SIOCDEVPRIVATE";
+		goto found_method;
+	}
+
+	iface_status = detect_link_wlan();
+	if (iface_status != IFSTATUS_ERR) {
+		G.cached_detect_link_func = detect_link_wlan;
+		method = "wireless extension";
+		goto found_method;
+	}
+
+	iface_status = detect_link_iff();
+	if (iface_status != IFSTATUS_ERR) {
+		G.cached_detect_link_func = detect_link_iff;
+		method = "IFF_RUNNING";
+		goto found_method;
+	}
+
+	logmode = sv_logmode;
+	return iface_status; /* IFSTATUS_ERR */
+}
+
+static smallint detect_link(void)
+{
+	smallint status;
+
+	if (!G.iface_exists)
+		return (option_mask32 & FLAG_MONITOR) ? IFSTATUS_DOWN : IFSTATUS_ERR;
+
+#if 0
+/* Why? This behavior makes it hard to temporary down the iface.
+ * It makes a bit more sense to do only in maybe_up_new_iface.
+ * OTOH, maybe detect_link_wlan needs this. Then it should be done
+ * _only_ there.
+ */
+	if (!(option_mask32 & FLAG_NO_AUTO))
+		up_iface();
+#endif
+
+	status = G.detect_link_func();
+	if (status == IFSTATUS_ERR) {
+		if (option_mask32 & FLAG_IGNORE_FAIL)
+			status = IFSTATUS_DOWN;
+		if (option_mask32 & FLAG_IGNORE_FAIL_POSITIVE)
+			status = IFSTATUS_UP;
+	}
+
+	if (status == IFSTATUS_ERR
+	 && G.detect_link_func == detect_link_auto
+	) {
+		bb_error_msg("failed to detect link status");
+	}
+
+	if (status != G.iface_last_status) {
+//TODO: is it safe to repeatedly do this?
+		setenv(IFPLUGD_ENV_PREVIOUS, strstatus(G.iface_last_status), 1);
+		setenv(IFPLUGD_ENV_CURRENT, strstatus(status), 1);
+		G.iface_last_status = status;
+	}
+
+	return status;
+}
+
+static NOINLINE int check_existence_through_netlink(void)
+{
+	char replybuf[1024];
+
+	while (1) {
+		struct nlmsghdr *mhdr;
+		ssize_t bytes;
+
+		bytes = recv(netlink_fd, &replybuf, sizeof(replybuf), MSG_DONTWAIT);
+		if (bytes < 0) {
+			if (errno == EAGAIN)
+				return G.iface_exists;
+			if (errno == EINTR)
+				continue;
+
+			bb_perror_msg("netlink: recv");
+			return -1;
+		}
+
+		mhdr = (struct nlmsghdr*)replybuf;
+		while (bytes > 0) {
+			if (!NLMSG_OK(mhdr, bytes)
+			 || bytes < sizeof(struct nlmsghdr)
+			 || bytes < mhdr->nlmsg_len
+			) {
+				bb_error_msg("netlink packet too small or truncated");
+				return -1;
+			}
+
+			if (mhdr->nlmsg_type == RTM_NEWLINK || mhdr->nlmsg_type == RTM_DELLINK) {
+				struct rtattr *attr;
+				struct ifinfomsg *imsg;
+				int attr_len;
+
+				imsg = NLMSG_DATA(mhdr);
+
+				if (mhdr->nlmsg_len < NLMSG_LENGTH(sizeof(struct ifinfomsg))) {
+					bb_error_msg("netlink packet too small or truncated");
+					return -1;
+				}
+
+				attr = (struct rtattr*)((char*)imsg + NLMSG_ALIGN(sizeof(struct ifinfomsg)));
+				attr_len = NLMSG_PAYLOAD(mhdr, sizeof(struct ifinfomsg));
+
+				while (RTA_OK(attr, attr_len)) {
+					if (attr->rta_type == IFLA_IFNAME) {
+						char ifname[IFNAMSIZ + 1];
+						int len = RTA_PAYLOAD(attr);
+
+						if (len > IFNAMSIZ)
+							len = IFNAMSIZ;
+						memcpy(ifname, RTA_DATA(attr), len);
+						if (strcmp(G.iface, ifname) == 0) {
+							G.iface_exists = (mhdr->nlmsg_type == RTM_NEWLINK);
+						}
+					}
+					attr = RTA_NEXT(attr, attr_len);
+				}
+			}
+
+			mhdr = NLMSG_NEXT(mhdr, bytes);
+		}
+	}
+
+	return G.iface_exists;
+}
+
+static NOINLINE int netlink_open(void)
+{
+	int fd;
+	struct sockaddr_nl addr;
+
+	fd = xsocket(PF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);
+
+	memset(&addr, 0, sizeof(addr));
+	addr.nl_family = AF_NETLINK;
+	addr.nl_groups = RTMGRP_LINK;
+	addr.nl_pid = getpid();
+
+	xbind(fd, (struct sockaddr*)&addr, sizeof(addr));
+
+	return fd;
+}
+
+static NOINLINE pid_t read_pid(const char *filename)
+{
+	int len;
+	char buf[128];
+
+	len = open_read_close(filename, buf, 127);
+	if (len > 0) {
+		buf[len] = '\0';
+		/* returns ULONG_MAX on error => -1 */
+		return bb_strtoul(buf, NULL, 10);
+	}
+	return 0;
+}
+
+int ifplugd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int ifplugd_main(int argc UNUSED_PARAM, char **argv)
+{
+	int iface_status;
+	int delay_time;
+	const char *iface_status_str;
+	struct pollfd netlink_pollfd[1];
+	unsigned opts;
+#if ENABLE_FEATURE_PIDFILE
+	char *pidfile_name;
+	pid_t pid_from_pidfile;
+#endif
+
+	INIT_G();
+
+	opt_complementary = "t+:u+:d+";
+	opts = getopt32(argv, OPTION_STR,
+		&G.iface, &G.script_name, &G.poll_time, &G.delay_up,
+		&G.delay_down, &G.api_mode, &G.extra_arg);
+
+	applet_name = xasprintf("ifplugd(%s)", G.iface);
+
+#if ENABLE_FEATURE_PIDFILE
+	pidfile_name = xasprintf(_PATH_VARRUN"ifplugd.%s.pid", G.iface);
+	pid_from_pidfile = read_pid(pidfile_name);
+
+	if (opts & FLAG_KILL) {
+		if (pid_from_pidfile > 0)
+			kill(pid_from_pidfile, SIGQUIT);
+		return EXIT_SUCCESS;
+	}
+
+	if (pid_from_pidfile > 0 && kill(pid_from_pidfile, 0) == 0)
+		bb_error_msg_and_die("daemon already running");
+#endif
+
+	switch (G.api_mode[0]) {
+	case API_AUTO:
+		G.detect_link_func = detect_link_auto;
+		break;
+	case API_ETHTOOL:
+		G.detect_link_func = detect_link_ethtool;
+		break;
+	case API_MII:
+		G.detect_link_func = detect_link_mii;
+		break;
+	case API_PRIVATE:
+		G.detect_link_func = detect_link_priv;
+		break;
+	case API_WLAN:
+		G.detect_link_func = detect_link_wlan;
+		break;
+	case API_IFF:
+		G.detect_link_func = detect_link_iff;
+		break;
+	default:
+		bb_error_msg_and_die("unknown API mode '%s'", G.api_mode);
+	}
+
+	if (!(opts & FLAG_NO_DAEMON))
+		bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
+
+	xmove_fd(xsocket(AF_INET, SOCK_DGRAM, 0), ioctl_fd);
+	if (opts & FLAG_MONITOR) {
+		xmove_fd(netlink_open(), netlink_fd);
+	}
+
+	write_pidfile(pidfile_name);
+
+	/* this can't be moved before socket creation */
+	if (!(opts & FLAG_NO_SYSLOG)) {
+		openlog(applet_name, 0, LOG_DAEMON);
+		logmode |= LOGMODE_SYSLOG;
+	}
+
+	bb_signals(0
+		| (1 << SIGINT )
+		| (1 << SIGTERM)
+		| (1 << SIGQUIT)
+		| (1 << SIGHUP ) /* why we ignore it? */
+		/* | (1 << SIGCHLD) - run_script does not use it anymore */
+		, record_signo);
+
+	bb_error_msg("started: %s", bb_banner);
+
+	if (opts & FLAG_MONITOR) {
+		struct ifreq ifrequest;
+		set_ifreq_to_ifname(&ifrequest);
+		G.iface_exists = (network_ioctl(SIOCGIFINDEX, &ifrequest) == 0);
+	}
+
+	if (G.iface_exists)
+		maybe_up_new_iface();
+
+	iface_status = detect_link();
+	if (iface_status == IFSTATUS_ERR)
+		goto exiting;
+	iface_status_str = strstatus(iface_status);
+
+	if (opts & FLAG_MONITOR) {
+		bb_error_msg("interface %s",
+			G.iface_exists ? "exists"
+			: "doesn't exist, waiting");
+	}
+	/* else we assume it always exists, but don't mislead user
+	 * by potentially lying that it really exists */
+
+	if (G.iface_exists) {
+		bb_error_msg("link is %s", iface_status_str);
+	}
+
+	if ((!(opts & FLAG_NO_STARTUP)
+	     && iface_status == IFSTATUS_UP
+	    )
+	 || (opts & FLAG_INITIAL_DOWN)
+	) {
+		if (run_script(iface_status_str) != 0)
+			goto exiting;
+	}
+
+	/* Main loop */
+	netlink_pollfd[0].fd = netlink_fd;
+	netlink_pollfd[0].events = POLLIN;
+	delay_time = 0;
+	while (1) {
+		int iface_status_old;
+		int iface_exists_old;
+
+		switch (bb_got_signal) {
+		case SIGINT:
+		case SIGTERM:
+			bb_got_signal = 0;
+			goto cleanup;
+		case SIGQUIT:
+			bb_got_signal = 0;
+			goto exiting;
+		default:
+			bb_got_signal = 0;
+			break;
+		}
+
+		if (poll(netlink_pollfd,
+				(opts & FLAG_MONITOR) ? 1 : 0,
+				G.poll_time * 1000
+			) < 0
+		) {
+			if (errno == EINTR)
+				continue;
+			bb_perror_msg("poll");
+			goto exiting;
+		}
+
+		iface_status_old = iface_status;
+		iface_exists_old = G.iface_exists;
+
+		if ((opts & FLAG_MONITOR)
+		 && (netlink_pollfd[0].revents & POLLIN)
+		) {
+			G.iface_exists = check_existence_through_netlink();
+			if (G.iface_exists < 0) /* error */
+				goto exiting;
+			if (iface_exists_old != G.iface_exists) {
+				bb_error_msg("interface %sappeared",
+						G.iface_exists ? "" : "dis");
+				if (G.iface_exists)
+					maybe_up_new_iface();
+			}
+		}
+
+		/* note: if !G.iface_exists, returns DOWN */
+		iface_status = detect_link();
+		if (iface_status == IFSTATUS_ERR) {
+			if (!(opts & FLAG_MONITOR))
+				goto exiting;
+			iface_status = IFSTATUS_DOWN;
+		}
+		iface_status_str = strstatus(iface_status);
+
+		if (iface_status_old != iface_status) {
+			bb_error_msg("link is %s", iface_status_str);
+
+			if (delay_time) {
+				/* link restored its old status before
+				 * we run script. don't run the script: */
+				delay_time = 0;
+			} else {
+				delay_time = monotonic_sec();
+				if (iface_status == IFSTATUS_UP)
+					delay_time += G.delay_up;
+				if (iface_status == IFSTATUS_DOWN)
+					delay_time += G.delay_down;
+				if (delay_time == 0)
+					delay_time++;
+			}
+		}
+
+		if (delay_time && (int)(monotonic_sec() - delay_time) >= 0) {
+			delay_time = 0;
+			if (run_script(iface_status_str) != 0)
+				goto exiting;
+		}
+	} /* while (1) */
+
+ cleanup:
+	if (!(opts & FLAG_NO_SHUTDOWN)
+	 && (iface_status == IFSTATUS_UP
+	     || (iface_status == IFSTATUS_DOWN && delay_time)
+	    )
+	) {
+		setenv(IFPLUGD_ENV_PREVIOUS, strstatus(iface_status), 1);
+		setenv(IFPLUGD_ENV_CURRENT, strstatus(-1), 1);
+		run_script("down\0up"); /* reusing string */
+	}
+
+ exiting:
+	remove_pidfile(pidfile_name);
+	bb_error_msg_and_die("exiting");
+}