/*
- * Monitor hosts using ICMP "echo" and notify when down.
- * TODO: Write a better description.
+ * ICMPmonitor
+ *
+ * Monitors hosts using ICMP 'echo', executing a user-specified command
+ * whenever hosts change state between responsive and unresponsive.
*
* © 2019 Aaron Taylor <ataylor at subgeniuskitty dot com>
* © 1999 Vadim Zaliva <lord@crocodile.org>
* © 1989 The Regents of the University of California & Mike Muuss
+ *
* See LICENSE file for copyright and license details.
*/
+/* Wishlist */
+/* TODO: Add IPv6 support. */
+/* TODO: Turn the global '-r' functionality into per-host config file option. */
+/* TODO: Add 'auto' keyword to 'start_condition', testing host on startup. */
+/* TODO: Double-check the network code when interrupted while receiving a packet. */
+
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <errno.h>
+#include <assert.h>
+
#include "iniparser/iniparser.h"
-#define MAXPACKETSIZE (65536 - 60 - 8) /* TODO: What are the magic numbers? */
-#define DEFAULTDATALEN (64 - 8) /* TODO: What are the magic numbers? */
+#define VERSION 2
+
+/* ICMP header contains: type, code, checksum, identifier and sequence number. */
+#define ICMP_ECHO_HEADER_BYTES 8
+#define ICMP_ECHO_DATA_BYTES sizeof(struct timeval)
+#define ICMP_ECHO_PACKET_BYTES ICMP_ECHO_HEADER_BYTES + ICMP_ECHO_DATA_BYTES
+#define IP_PACKET_MAX_BYTES 65535
-/* Must be larger than the length of the longest configuration key (currently 'start_condition'). */
-#define MAXCONFKEYLEN 20
+/* Minimum time in seconds between pings. If this value is increased above the */
+/* `ping_interval` for a given host, some pings to that host may not be sent. */
+#define TIMER_RESOLUTION 1
+
+/* Must be larger than the length of the longest configuration key (not value). */
+/* For example: MAX_CONF_KEY_LEN > strlen("start_condition") */
+#define MAX_CONF_KEY_LEN 20
/* One struct per host as listed in the config file. */
-struct monitor_host {
+struct host_entry {
/* From the config file */
char * name;
int ping_interval;
int max_delay;
- char * upcmd;
- char * downcmd;
+ char * up_cmd;
+ char * down_cmd;
/* Calculated values */
int socket;
struct timeval last_ping_received;
struct timeval last_ping_sent;
- bool hostup;
+ bool host_up;
struct sockaddr_in dest;
- unsigned int sentpackets;
- unsigned int recvdpackets;
/* Linked list */
- struct monitor_host * next;
+ struct host_entry * next;
};
/* Globals */
/* Since the program is based around signals, a linked list of hosts is maintained here. */
- static struct monitor_host ** hosts = NULL;
+ struct host_entry * first_host_in_list = NULL;
/* Set by command line flags. */
- static bool verbose = false;
- static bool retry_down_cmd = false;
- /* TODO: Get rid of this global. */
- static int send_delay = 1;
+ bool verbose = false;
+ bool retry_down_cmd = false;
/*
- * Checksum routine for Internet Protocol family headers
+ * Generate an Internet Checksum per RFC 1071.
+ *
+ * This is not a general purpose implementation of RFC 1071. Since we only
+ * send ICMP echo packets, we assume 'data' will contain a specific number of
+ * bytes.
*/
-static int
-in_cksum(unsigned short * addr, int len)
+uint16_t
+checksum(const uint16_t * data)
{
- int nleft = len;
- unsigned short * w = addr;
- int sum = 0;
- unsigned short answer = 0;
-
- /*
- * Our algorithm is simple, using a 32 bit accumulator (sum), we add
- * sequential 16 bit words to it, and at the end, fold back all the
- * carry bits from the top 16 bits into the lower 16 bits.
- */
- while (nleft > 1) {
- sum += *w++;
- nleft -= 2;
- }
-
- /* mop up an odd byte, if necessary */
- if (nleft == 1) {
- *(u_char *)(&answer) = *(u_char *)w;
- sum += answer;
+ uint32_t accumulator = 0;
+ for (size_t i = 0; i < ICMP_ECHO_PACKET_BYTES / 2; i++) {
+ accumulator += ntohs(data[i]);
+ if (accumulator > 0xffff) accumulator -= 0xffff;
}
-
- /* add back carry outs from top 16 bits to low 16 bits */
- sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */
- sum += (sum >> 16); /* add carry */
- answer = ~sum; /* truncate to 16 bits */
- return(answer);
+ return htons(~accumulator);
}
/*
- * Subtracts two timeval structs.
- * Ensure out >= in.
- * Modifies out = out - in.
+ * Calculate difference (a-b) between two timeval structs.
*/
-static void
-tv_sub(register struct timeval * out, register struct timeval * in)
+void
+timeval_diff(struct timeval * a, const struct timeval * b)
{
- if ((out->tv_usec -= in->tv_usec) < 0) {
- --out->tv_sec;
- out->tv_usec += 1000000;
+ if (a->tv_usec < b->tv_usec) {
+ a->tv_sec--;
+ a->tv_usec += 1000000;
}
- out->tv_sec -= in->tv_sec;
+ a->tv_usec -= b->tv_usec;
+ a->tv_sec -= b->tv_sec;
}
/*
- * Compose and transmit an ICMP ECHO REQUEST packet. The IP packet
- * will be added on by the kernel. The ID field is our UNIX process ID,
- * and the sequence number is an ascending integer. The first 8 bytes
- * of the data portion are used to hold a UNIX "timeval" struct in VAX
- * byte-order, to compute the round-trip time.
+ * This function iterates over the list of hosts, pinging any which are due.
*/
-static void
-pinger(int ignore)
+void
+pinger(int ignore) /* Dummy parameter since this function registers as a signal handler. */
{
- int cc, i;
- struct icmp * icp;
- struct monitor_host * p;
- u_char outpack[MAXPACKETSIZE];
-
- p = hosts[0];
- while (p) {
- if (p->socket != -1) {
- struct timeval now;
-
- gettimeofday(&now, (struct timezone *) NULL);
- tv_sub(&now, &p->last_ping_received);
-
- if (now.tv_sec > (p->max_delay + p->ping_interval)) {
- if ((p->hostup) || retry_down_cmd) {
- if (verbose) printf("INFO: Host %s stopped responding. Executing DOWN command.\n", p->name);
- p->hostup = false;
- if (!fork()) {
- system(p->downcmd);
- exit(EXIT_SUCCESS);
- } else {
- wait(NULL);
- }
- }
- }
+ assert(first_host_in_list);
- gettimeofday(&now, (struct timezone *) NULL);
- tv_sub(&now, &p->last_ping_sent);
+ struct icmp * icmp_packet;
+ struct host_entry * host = first_host_in_list;
+ unsigned char packet[IP_PACKET_MAX_BYTES]; /* Use char so this can be aliased later. */
- if (now.tv_sec > p->ping_interval) { /* Time to send ping */
- icp = (struct icmp *) outpack;
- icp->icmp_type = ICMP_ECHO;
- icp->icmp_code = 0;
- icp->icmp_cksum = 0;
- icp->icmp_seq = p->socket;
- icp->icmp_id = getpid() & 0xFFFF;
+ while (host) {
+ struct timeval elapsed_time;
+ gettimeofday(&elapsed_time, NULL);
+ timeval_diff(&elapsed_time, &host->last_ping_received);
- if (verbose) printf("INFO: Sending ICMP packet to %s.\n", p->name);
+ if ((elapsed_time.tv_sec > host->max_delay) && (host->host_up || retry_down_cmd)) {
+ if (verbose) printf("INFO: Host %s stopped responding. Executing DOWN command.\n", host->name);
+ host->host_up = false;
+ if (!fork()) {
+ system(host->down_cmd);
+ exit(EXIT_SUCCESS);
+ }
+ }
- gettimeofday((struct timeval *) &outpack[8], (struct timezone *) NULL);
+ if (elapsed_time.tv_sec > host->ping_interval) {
+ if (verbose) printf("INFO: Sending ICMP packet to %s.\n", host->name);
- cc = DEFAULTDATALEN + 8; /* skips ICMP portion */
+ icmp_packet = (struct icmp *) packet;
+ icmp_packet->icmp_type = ICMP_ECHO;
+ icmp_packet->icmp_code = 0;
+ icmp_packet->icmp_cksum = 0;
+ icmp_packet->icmp_seq = host->socket;
+ icmp_packet->icmp_id = getpid() & 0xFFFF;
- /* compute ICMP checksum */
- icp->icmp_cksum = in_cksum((unsigned short *) icp, cc);
+ /* Write a timestamp struct in the packet's data segment for use in calculating travel times. */
+ gettimeofday((struct timeval *) &packet[ICMP_ECHO_HEADER_BYTES], NULL);
- i = sendto(p->socket, (char *) outpack, cc, 0, (const struct sockaddr *) (&p->dest), sizeof(struct sockaddr));
+ icmp_packet->icmp_cksum = checksum((uint16_t *) packet);
- gettimeofday(&p->last_ping_sent, (struct timezone *) NULL);
+ size_t bytes_sent = sendto(host->socket, packet, ICMP_ECHO_PACKET_BYTES, 0,
+ (const struct sockaddr *) &host->dest,
+ sizeof(struct sockaddr));
- if (i < 0 || i != cc) {
- if (i<0) fprintf(stderr, "WARN: Failed sending ICMP packet to %s.\n", p->name);
- }
- p->sentpackets++;
+ if (bytes_sent == ICMP_ECHO_PACKET_BYTES) {
+ gettimeofday(&host->last_ping_sent, NULL);
+ } else {
+ fprintf(stderr, "WARN: Failed sending ICMP packet to %s.\n", host->name);
}
}
- p = p->next;
+ host = host->next;
}
- signal(SIGALRM, pinger); /* restore handler */
- alarm(send_delay);
+ signal(SIGALRM, pinger);
+ alarm(TIMER_RESOLUTION);
}
-static void
-read_icmp_data(struct monitor_host * p)
+void
+read_icmp_data(struct host_entry * host)
{
- int cc, iphdrlen, delay;
- socklen_t fromlen;
- struct sockaddr_in from;
- struct ip * ip;
- struct icmp * icmp;
- struct timeval tv;
- unsigned char buf[MAXPACKETSIZE];
-
- gettimeofday(&tv, (struct timezone *) NULL);
+ struct timeval now;
+ gettimeofday(&now, NULL);
- fromlen = sizeof(from);
- if ((cc = recvfrom(p->socket, buf, sizeof(buf), 0, (struct sockaddr *)&from, &fromlen)) < 0) {
- if (errno != EINTR) fprintf(stderr, "WARN: Error reading ICMP data from %s.\n", p->name);
+ struct sockaddr_in from;
+ socklen_t fromlen = sizeof(from);
+ int bytes;
+ unsigned char packet[IP_PACKET_MAX_BYTES]; /* Use char so this can be aliased later. */
+ if ((bytes = recvfrom(host->socket, packet, sizeof(packet), 0, (struct sockaddr *) &from, &fromlen)) < 0) {
+ if (errno != EINTR) fprintf(stderr, "WARN: Error reading ICMP data from %s.\n", host->name);
return;
}
- /* check IP header actual len */
- ip = (struct ip *) buf;
- iphdrlen = ip->ip_hl << 2;
- icmp = (struct icmp *) (buf + iphdrlen);
+ struct ip * ip = (struct ip *) packet;
+ int iphdrlen = ip->ip_hl << 2;
+ struct icmp * icmp = (struct icmp *) (packet + iphdrlen);
- if (cc < iphdrlen + ICMP_MINLEN) {
- fprintf(stderr, "WARN: Received short packet from %s.\n", p->name);
+ if (bytes < iphdrlen + ICMP_MINLEN) {
+ fprintf(stderr, "WARN: Received short packet from %s.\n", host->name);
return;
}
- if (icmp->icmp_type == ICMP_ECHOREPLY && icmp->icmp_id == (getpid() & 0xFFFF) && icmp->icmp_seq == p->socket) {
- p->recvdpackets++;
-
- memcpy(&p->last_ping_received, &tv, sizeof(tv));
-
- tv_sub(&tv, (struct timeval *) &icmp->icmp_data[0]);
- delay = tv.tv_sec * 1000 + (tv.tv_usec / 1000);
-
- if (verbose) printf("INFO: Got ICMP reply from %s in %d ms.\n", p->name, delay);
- if (!p->hostup) {
- if (verbose) printf("INFO: Host %s started responding. Executing UP command.\n", p->name);
- p->hostup = true;
+ if (icmp->icmp_type == ICMP_ECHOREPLY && icmp->icmp_id == (getpid() & 0xFFFF) && icmp->icmp_seq == host->socket) {
+ memcpy(&host->last_ping_received, &now, sizeof(now));
+ if (verbose) printf("INFO: Got ICMP reply from %s.\n", host->name);
+ if (!host->host_up) {
+ if (verbose) printf("INFO: Host %s started responding. Executing UP command.\n", host->name);
+ host->host_up = true;
if (!fork()) {
- system(p->upcmd);
+ system(host->up_cmd);
exit(EXIT_SUCCESS);
- } else {
- wait(NULL);
}
}
} else {
- /* TODO: Do anything here? */
+ /* The packet isn't what we expected. Ignore it and move on. */
}
}
-static void
+/*
+ * This function contains the main program loop, listening for replies to pings
+ * sent from the signal-driven pinger().
+ */
+void
get_response(void)
{
- fd_set rfds;
- int retval, maxd = -1;
- struct monitor_host * p;
-
- while (1) {
- p = hosts[0];
+ while (true) {
+ fd_set rfds;
FD_ZERO(&rfds);
- while (p) {
- if (p->socket != -1) {
- if (p->socket > maxd) maxd=p->socket;
- FD_SET(p->socket, &rfds);
- }
- p = p->next;
+
+ assert(first_host_in_list);
+ struct host_entry * host = first_host_in_list;
+
+ int max_fd = -1;
+ while (host) {
+ if (host->socket > max_fd) max_fd = host->socket;
+ FD_SET(host->socket, &rfds);
+ host = host->next;
}
- retval = select(maxd+1, &rfds, NULL, NULL, NULL);
- if (retval < 0) {
- /* Intentionally empty. We arrive here when interrupted by a signal. No action should be taken. */
- } else {
- if (retval > 0) {
- p = hosts[0];
- while (p) {
- if (p->socket!=-1 && FD_ISSET(p->socket, &rfds)) read_icmp_data(p);
- p = p->next;
- }
- } else {
- /* TODO: How to handle this error? */
+ int retval;
+ if ((retval = select(max_fd+1, &rfds, NULL, NULL, NULL)) > 0) {
+ assert(first_host_in_list);
+ host = first_host_in_list;
+ while (host) {
+ if (FD_ISSET(host->socket, &rfds)) read_icmp_data(host);
+ host = host->next;
}
+ } else {
+ /* An error or interruption occurred. */
+ /* We can't do anything about it, so loop and try again. */
}
}
}
/*
- * Parses `config_file` and creates relevant entries under the global variable `hosts`.
+ * Parse a configuration file using the `iniparser` library.
+ * See `icmpmonitor.ini` and `README.md` for examples and reference.
*/
-static void
+void
parse_config(const char * conf_file)
{
dictionary * conf = iniparser_load(conf_file);
exit(EXIT_FAILURE);
}
- hosts = malloc(sizeof(struct monitor_host *) * host_count);
+ struct host_entry * host_list_end = NULL;
for (int i=0; i < host_count; i++) {
- /* Allocate a buffer large enough to hold the full 'section:key' string. */
+ /* Allocate a reusable buffer large enough to hold the full 'section:key' string. */
int section_len = strlen(iniparser_getsecname(conf, i));
- char * key_buf = malloc(section_len + 1 + MAXCONFKEYLEN + 1);
+ char * key_buf = malloc(section_len + 1 + MAX_CONF_KEY_LEN + 1); /* +1 for ':' and '\0' */
strcpy(key_buf, iniparser_getsecname(conf, i));
key_buf[section_len++] = ':';
- hosts[i] = malloc(sizeof(struct monitor_host));
- for (int k=0; k<6; k++) {
- key_buf[section_len] = '\0'; /* Reuse the section name and colon on each pass through this loop. */
- switch (k) {
- case 0:
- strncat(key_buf, "host", MAXCONFKEYLEN);
- hosts[i]->name = strdup(iniparser_getstring(conf, key_buf, NULL));
- break;
- case 1:
- strncat(key_buf, "interval", MAXCONFKEYLEN);
- hosts[i]->ping_interval = iniparser_getint(conf, key_buf, -1);
- break;
- case 2:
- strncat(key_buf, "max_delay", MAXCONFKEYLEN);
- hosts[i]->max_delay = iniparser_getint(conf, key_buf, -1);
- break;
- case 3:
- strncat(key_buf, "up_cmd", MAXCONFKEYLEN);
- hosts[i]->upcmd = strdup(iniparser_getstring(conf, key_buf, NULL));
- break;
- case 4:
- strncat(key_buf, "down_cmd", MAXCONFKEYLEN);
- hosts[i]->downcmd = strdup(iniparser_getstring(conf, key_buf, NULL));
- break;
- case 5:
- /* TODO: Parse for up/down/auto in start_condition. */
- /* TODO: Do a host up/down check if necessary. */
- hosts[i]->hostup = true;
- break;
- }
- }
- /* TODO: Do I want to make any checks for up_cmd, down_cmd, and start_condition? */
- if (hosts[i]->name == NULL || hosts[i]->ping_interval == -1 || hosts[i]->max_delay == -1) {
+ struct host_entry * cur_host = malloc(sizeof(struct host_entry));
+
+ key_buf[section_len] = '\0';
+ strncat(key_buf, "host", MAX_CONF_KEY_LEN);
+ cur_host->name = strdup(iniparser_getstring(conf, key_buf, NULL));
+
+ key_buf[section_len] = '\0';
+ strncat(key_buf, "interval", MAX_CONF_KEY_LEN);
+ cur_host->ping_interval = iniparser_getint(conf, key_buf, -1);
+
+ key_buf[section_len] = '\0';
+ strncat(key_buf, "max_delay", MAX_CONF_KEY_LEN);
+ cur_host->max_delay = iniparser_getint(conf, key_buf, -1);
+
+ key_buf[section_len] = '\0';
+ strncat(key_buf, "up_cmd", MAX_CONF_KEY_LEN);
+ cur_host->up_cmd = strdup(iniparser_getstring(conf, key_buf, NULL));
+
+ key_buf[section_len] = '\0';
+ strncat(key_buf, "down_cmd", MAX_CONF_KEY_LEN);
+ cur_host->down_cmd = strdup(iniparser_getstring(conf, key_buf, NULL));
+
+ key_buf[section_len] = '\0';
+ strncat(key_buf, "start_condition", MAX_CONF_KEY_LEN);
+ const char * value = iniparser_getstring(conf, key_buf, NULL);
+ if (value) cur_host->host_up = *value == 'u' ? true : false;
+
+ if (cur_host->name == NULL || cur_host->ping_interval == -1 || cur_host->max_delay == -1) {
fprintf(stderr, "ERROR: Problems parsing section %s.\n", iniparser_getsecname(conf, i));
exit(EXIT_FAILURE);
}
- hosts[i]->sentpackets = 0;
- hosts[i]->recvdpackets = 0;
- hosts[i]->socket = -1;
- hosts[i]->next = NULL;
- if (i>0) hosts[i-1]->next = hosts[i];
- gettimeofday(&(hosts[i]->last_ping_received), (struct timezone *) NULL);
+ cur_host->socket = -1;
+ cur_host->next = NULL;
+ gettimeofday(&(cur_host->last_ping_received), (struct timezone *) NULL);
+
+ if (first_host_in_list == NULL) {
+ first_host_in_list = cur_host;
+ host_list_end = cur_host;
+ } else {
+ host_list_end->next = cur_host;
+ host_list_end = cur_host;
+ }
+
+ free(key_buf);
}
iniparser_freedict(conf);
}
-static int
+/*
+ * Parse string (IP or hostname) to Internet address.
+ *
+ * Returns 0 if host can't be resolved, otherwise returns an Internet address.
+ */
+uint32_t
get_host_addr(const char * name)
{
- static int res;
- struct hostent * he;
-
- if ((res = inet_addr(name)) < 0) {
- he = gethostbyname(name);
- if (!he) return -1;
- memcpy(&res, he->h_addr, he->h_length);
- }
- return(res);
+ struct addrinfo hints;
+ memset(&hints, 0, sizeof(hints));
+ hints.ai_family = AF_INET;
+
+ int rv;
+ struct addrinfo * address;
+ if ((rv = getaddrinfo(name, NULL, &hints, &address)) != 0) return 0;
+ uint32_t result = ((struct sockaddr_in *)(address->ai_addr))->sin_addr.s_addr;
+ freeaddrinfo(address);
+ return result;
}
-static int
-gcd(int x, int y)
+void
+remove_host_from_list(struct host_entry * host)
{
- int remainder = x % y;
- if (remainder == 0) return y;
- return gcd(y, remainder);
+ assert(first_host_in_list);
+ assert(host);
+
+ if (host == first_host_in_list) {
+ first_host_in_list = host->next;
+ } else {
+ struct host_entry * temp = first_host_in_list;
+ while (temp->next != host && temp->next != NULL) temp = temp->next;
+ if (temp->next == NULL) return;
+ temp->next = temp->next->next;
+ }
+ free(host);
}
-static void
+void
init_hosts(void)
{
- struct monitor_host * p = hosts[0];
+ struct host_entry * host;
struct protoent * proto;
- int ok = 0;
if ((proto = getprotobyname("icmp")) == NULL) {
fprintf(stderr, "ERROR: Unknown protocol: icmp.\n");
exit(EXIT_FAILURE);
}
- while (p) {
- bzero(&p->dest, sizeof(p->dest));
- p->dest.sin_family = AF_INET;
- if ((p->dest.sin_addr.s_addr = get_host_addr(p->name)) <= 0) {
- fprintf(stderr, "WARN: Can't resolve host. Skipping client %s.\n", p->name);
- p->socket=-1;
- } else {
- if ((p->socket = socket(AF_INET,SOCK_RAW,proto->p_proto)) < 0) {
- fprintf(stderr, "WARN: Can't create socket. Skipping client %s.\n", p->name);
- p->socket=-1;
- } else {
- if (ok == 0) send_delay = p->ping_interval;
- else send_delay = gcd(send_delay, p->ping_interval);
- ok++;
- }
+ assert(first_host_in_list);
+ host = first_host_in_list;
+ while (host) {
+ struct host_entry * next_host = host->next;
+ bzero(&host->dest, sizeof(host->dest));
+ host->dest.sin_family = AF_INET;
+ if (!(host->dest.sin_addr.s_addr = get_host_addr(host->name))) {
+ fprintf(stderr, "WARN: Removing unresolvable host %s from list.\n", host->name);
+ remove_host_from_list(host);
}
- p = p->next;
+ host = next_host;
}
- if (!ok) {
- fprintf(stderr, "ERROR: No hosts left to process.\n");
- exit(EXIT_FAILURE);
+ assert(first_host_in_list);
+ host = first_host_in_list;
+ while (host) {
+ struct host_entry * next_host = host->next;
+ if ((host->socket = socket(AF_INET, SOCK_RAW, proto->p_proto)) < 0) {
+ fprintf(stderr, "WARN: Failed creating socket. Removing host %s from list.\n", host->name);
+ remove_host_from_list(host);
+ }
+ host = next_host;
}
}
void
-print_usage(void)
+print_usage(char ** argv)
{
- fprintf(stderr,"Usage: icmpmonitor [-v] [-r] [-f cfgfile]\n");
+ printf( "ICMPmonitor v%d (www.subgeniuskitty.com)\n"
+ "Usage: %s [-h] [-v] [-r] -f <file>\n"
+ " -v Verbose mode. Prints message for each packet sent and received.\n"
+ " -r Repeat down_cmd every time a host fails to respond to a packet.\n"
+ " Note: Default behavior executes down_cmd only once, resetting once the host is back up.\n"
+ " -h Help (prints this message)\n"
+ " -f <file> Specify a configuration file.\n"
+ , VERSION, argv[0]);
}
void
parse_params(int argc, char ** argv)
{
int param;
- while ((param = getopt(argc, argv, "rvf:")) != -1) {
+ while ((param = getopt(argc, argv, "hrvf:")) != -1) {
switch(param) {
case 'v':
verbose = true;
case 'f':
parse_config(optarg);
break;
+ case 'h':
default:
- print_usage();
+ print_usage(argv);
exit(EXIT_FAILURE);
+ break;
}
}
- if (hosts == NULL) {
+ if (first_host_in_list == NULL) {
fprintf(stderr, "ERROR: Unable to parse a config file.\n");
+ print_usage(argv);
exit(EXIT_FAILURE);
}
}
int
main(int argc, char ** argv)
{
+ /* Parse the command line options, load and parse the config file. */
parse_params(argc, argv);
+ /* Process config for each host, generating/verifying any necessary information. */
init_hosts();
+ /* Make sure initialization left us with something useful. */
+ assert(first_host_in_list);
+
+ /* Pings are sent asynchronously. */
signal(SIGALRM, pinger);
- alarm(send_delay);
+ alarm(TIMER_RESOLUTION);
+ /* The main program loop listens for ping responses. */
get_response();
+ /* Should be unreachable. */
exit(EXIT_SUCCESS);
}