리눅스 routed 코드에 대해...

리눅스 처음다루는데 대뜸 이걸 분석해보라니 원....
라우팅 관련 routed소스 중 메인함수입니다...
분석하는데 도움을 주세요...

char copyright[] =
"@(#) Copyright (c) 1983, 1988, 1993\n\
The Regents of the University of California. All rights reserved.\n";
#if !defined(lint)
static char sccsid[] = "@(#)main.c 8.1 (Berkeley) 6/5/93";
#else
static char rcsid[] = "$OpenBSD: main.c,v 1.19 2005/03/23 18:06:07 jmc Exp $";
#endif

#include "defs.h"
#include "pathnames.h"
#ifdef sgi
#include "math.h"
#endif
#include
#include
#include
#include

pid_t mypid;

naddr myaddr; /* system address */
char myname[MAXHOSTNAMELEN];

int supplier; /* supply or broadcast updates */
int supplier_set;
int ipforwarding = 1; /* kernel forwarding on */

int default_gateway; /* 1=advertise default */
int background = 1;
int ridhosts; /* 1=reduce host routes */
int mhome; /* 1=want multi-homed host route */
int advertise_mhome; /* 1=must continue adverising it */
int auth_ok = 1; /* 1=ignore auth if we do not care */

struct timeval epoch; /* when started */
struct timeval clk, prev_clk;
struct timeval now; /* current idea of time */
time_t now_stale;
time_t now_expire;
time_t now_garbage;

struct timeval next_bcast; /* next general broadcast */
struct timeval no_flash = {EPOCH+SUPPLY_INTERVAL}; /* inhibit flash update */

fd_set *fdbitsp;
int sock_max;
int rip_sock = -1; /* RIP socket */
struct interface *rip_sock_mcast; /* current multicast interface */
int rt_sock; /* routing socket */
int rt_sock_seqno;

static int get_rip_sock(naddr, int);
static void timevalsub(struct timeval *, struct timeval *, struct timeval *);

int
main(int argc,
char *argv[])
{
int n, mib[4], off;
size_t len;
char *p, *q;
struct timeval wtime, t2;
time_t dt;
fd_set *ibitsp = NULL;
naddr p_addr, p_mask;
struct interface *ifp;
struct parm parm;
char *tracename = 0;

openlog("routed", LOG_PID | LOG_ODELAY, LOG_DAEMON); //프로그램 이름:routed, 소켓을 만듬
ftrace = stdout;

gettimeofday(&clk, 0); //현재 시스템 시간(마이크로초)
prev_clk = clk;
epoch = clk;
epoch.tv_sec -= EPOCH; //EPOCH=bias time
now.tv_sec = EPOCH;
now_stale = EPOCH - STALE_TIME;
now_expire = EPOCH - EXPIRE_TIME;
now_garbage = EPOCH - GARBAGE_TIME;
wtime.tv_sec = 0;

(void)gethostname(myname, sizeof(myname));
(void)gethost(myname, &myaddr);

while ((n = getopt(argc, argv, "sqdghmAtT:F:P:")) != -1) {
switch (n) {
case 's':
supplier = 1;
supplier_set = 1;
break;

case 'q':
supplier = 0;
supplier_set = 1;
break;

case 'd':
background = 0;
break;

case 'g':
bzero(&parm, sizeof(parm));
parm.parm_d_metric = 1;
p = check_parms(&parm);
if (p != 0)
msglog("bad -g: %s", p);
else
default_gateway = 1;
break;

case 'h': /* suppress extra host routes */
ridhosts = 1;
break;

case 'm': /* advertise host route */
mhome = 1; /* on multi-homed hosts */
break;

case 'A':
/* Ignore authentication if we do not care.
* Crazy as it is, that is what RFC 1723 requires.
*/
auth_ok = 0;
break;

case 't':
new_tracelevel++;
break;

case 'T':
tracename = optarg;
break;

case 'F': /* minimal routes for SLIP */
n = HOPCNT_INFINITY-2;
p = strchr(optarg,',');
if (p && *p != '\0') {
n = (int)strtoul(p+1, &q, 0);
if (*q == '\0'
&& n <= HOPCNT_INFINITY-1
&& n >= 1)
*p = '\0';
}
if (!getnet(optarg, &p_addr, &p_mask)) {
msglog("bad network; \"-F %s\"",
optarg);
break;
}
bzero(&parm, sizeof(parm));
parm.parm_addr_h = p_addr;
parm.parm_mask = p_mask;
parm.parm_d_metric = n;
p = check_parms(&parm);
if (p != 0)
msglog("bad -F: %s", p);
break;

case 'P':
/* handle arbirary, (usually) per-interface
* parameters.
*/
p = parse_parms(optarg);
if (p != 0)
msglog("bad \"%s\" in \"%s\"",
p, optarg);
break;

default:
goto usage;
}
}
argc -= optind;
argv += optind;

if (tracename == 0 && argc >= 1) {
tracename = *argv++;
argc--;
}
if (argc != 0) {
usage:
logbad(0, "usage: routed [-Adghmqst] [-F net[/mask][,metric]]"
" [-P parms] [-T tracefile]");
}
if (geteuid() != 0)
logbad(0, "requires UID 0");

mib[0] = CTL_NET;
mib[1] = PF_INET;
mib[2] = IPPROTO_IP;
mib[3] = IPCTL_FORWARDING;
len = sizeof(ipforwarding);
if (sysctl(mib, 4, &ipforwarding, &len, 0, 0) < 0)
LOGERR("sysctl(IPCTL_FORWARDING)");

if (!ipforwarding) {
if (supplier)
msglog("-s incompatible with ipforwarding=0");
if (default_gateway) {
msglog("-g incompatible with ipforwarding=0");
default_gateway = 0;
}
supplier = 0;
supplier_set = 1;
}
if (default_gateway) {
if (supplier_set && !supplier) {
msglog("-g and -q incompatible");
} else {
supplier = 1;
supplier_set = 1;
}
}

signal(SIGALRM, sigalrm);
if (!background)
signal(SIGHUP, sigterm); /* SIGHUP fatal during debugging */
else
signal(SIGHUP, SIG_IGN);
signal(SIGTERM, sigterm);
signal(SIGINT, sigterm);
signal(SIGUSR1, sigtrace_on);
signal(SIGUSR2, sigtrace_off);

/* get into the background */
if (background) {
#ifdef sgi
if (0 > _daemonize(_DF_NOCHDIR,
new_tracelevel == 0 ? -1 :
_FILENO,
new_tracelevel == 0 ? -1 : STDERR_FILENO,
-1))
BADERR(0, "_daemonize()");
#else
if (daemon(1, 1) < 0)
BADERR(0,"daemon()");
#endif
}

mypid = getpid();

/* prepare socket connected to the kernel.
*/
rt_sock = socket(AF_ROUTE, SOCK_RAW, 0);
if (rt_sock < 0)
BADERR(1,"rt_sock = socket()");
if (fcntl(rt_sock, F_SETFL, O_NONBLOCK) == -1)
logbad(1, "fcntl(rt_sock) O_NONBLOCK: %s", strerror(errno));
off = 0;
if (setsockopt(rt_sock, SOL_SOCKET,SO_USELOOPBACK,
&off,sizeof(off)) < 0)
LOGERR("setsockopt(SO_USELOOPBACK,0)");

fix_select();

if (background && new_tracelevel == 0)
ftrace = 0;
if (tracename != 0) {
trace_on(tracename, 1);
if (new_tracelevel == 0) /* use stdout if file is bad */
new_tracelevel = 1;
}
set_tracelevel();

/* initialize radix tree */
rtinit();

/* Pick a random part of the second for our output to minimize
* collisions.
*
* Start broadcasting after hearing from other routers, and
* at a random time so a bunch of systems do not get synchronized
* after a power failure.
*/
intvl_random(&next_bcast, EPOCH+MIN_WAITTIME, EPOCH+SUPPLY_INTERVAL);
age_timer.tv_usec = next_bcast.tv_usec;
age_timer.tv_sec = EPOCH+MIN_WAITTIME;
rdisc_timer = next_bcast;
ifinit_timer.tv_usec = next_bcast.tv_usec;

/* Collect an initial view of the world by checking the interface
* configuration and the kludge file.
*/
gwkludge();
ifinit();
flush_kern();

/* Ask for routes */
rip_query();
if (!supplier)
rdisc_sol();

/* Loop forever, listening and broadcasting.
*/
for (;;) {
prev_clk = clk;
gettimeofday(&clk, 0);
timevalsub(&t2, &clk, &prev_clk);
if (t2.tv_sec < 0
|| t2.tv_sec > wtime.tv_sec + 5) {
/* Deal with time changes before other housekeeping to
* keep everything straight.
*/
dt = t2.tv_sec;
if (dt > 0)
dt -= wtime.tv_sec;
trace_act("time changed by %d sec\n", dt);
epoch.tv_sec += dt;
}
timevalsub(&now, &clk, &epoch);
now_stale = now.tv_sec - STALE_TIME;
now_expire = now.tv_sec - EXPIRE_TIME;
now_garbage = now.tv_sec - GARBAGE_TIME;

/* deal with interrupts that should affect tracing */
set_tracelevel();

if (stopint != 0) {
if (supplier) {
rip_bcast(0);
rdisc_adv();
}
trace_off("exiting with signal %d\n", stopint);
exit(stopint | 128);
}

/* look for new or dead interfaces */
timevalsub(&wtime, &ifinit_timer, &now);
if (wtime.tv_sec <= 0) {
wtime.tv_sec = 0;
ifinit();
rip_query();
continue;
}

/* If it is time, then broadcast our routes.
*/
if (supplier || advertise_mhome) {
timevalsub(&t2, &next_bcast, &now);
if (t2.tv_sec <= 0) {
/* Synchronize the aging and broadcast
* timers to minimize awakenings
*/
age(0);

rip_bcast(0);

/* It is desirable to send routing updates
* regularly. So schedule the next update
* 30 seconds after the previous one was
* secheduled, instead of 30 seconds after
* the previous update was finished.
* Even if we just started after discovering
* a 2nd interface or were otherwise delayed,
* pick a 30-second aniversary of the
* original broadcast time.
*/
n = 1 + (0-t2.tv_sec)/SUPPLY_INTERVAL;
next_bcast.tv_sec += n*SUPPLY_INTERVAL;

continue;
}

if (timercmp(&t2, &wtime, <))
wtime = t2;
}

/* If we need a flash update, either do it now or
* set the delay to end when it is time.
*
* If we are within MIN_WAITTIME seconds of a full update,
* do not bother.
*/
if (need_flash
&& supplier
&& no_flash.tv_sec+MIN_WAITTIME < next_bcast.tv_sec) {
/* accurate to the millisecond */
if (!timercmp(&no_flash, &now, >))
rip_bcast(1);
timevalsub(&t2, &no_flash, &now);
if (timercmp(&t2, &wtime, <))
wtime = t2;
}

/* trigger the main aging timer.
*/
timevalsub(&t2, &age_timer, &now);
if (t2.tv_sec <= 0) {
age(0);
continue;
}
if (timercmp(&t2, &wtime, <))
wtime = t2;

/* update the kernel routing table
*/
timevalsub(&t2, &need_kern, &now);
if (t2.tv_sec <= 0) {
age(0);
continue;
}
if (timercmp(&t2, &wtime, <))
wtime = t2;

/* take care of router discovery,
* but do it to the millisecond
*/
if (!timercmp(&rdisc_timer, &now, >)) {
rdisc_age(0);
continue;
}
timevalsub(&t2, &rdisc_timer, &now);
if (timercmp(&t2, &wtime, <))
wtime = t2;

/* wait for input or a timer to expire.
*/
trace_flush();
if (ibitsp)
free(ibitsp);
ibitsp = (fd_set *)calloc(howmany(sock_max, NFDBITS),
sizeof(fd_mask));
if (ibitsp == NULL)
err(1, "calloc");
memcpy(ibitsp, fdbitsp, howmany(sock_max, NFDBITS) *
sizeof(fd_mask));
n = select(sock_max, ibitsp, 0, 0, &wtime);
if (n <= 0) {
if (n < 0 && errno != EINTR && errno != EAGAIN)
BADERR(1,"select");
continue;
}

if (FD_ISSET(rt_sock, ibitsp)) {
read_rt();
n--;
}
if (rdisc_sock >= 0 && FD_ISSET(rdisc_sock, ibitsp)) {
read_d();
n--;
}
if (rip_sock >= 0 && FD_ISSET(rip_sock, ibitsp)) {
read_rip(rip_sock, 0);
n--;
}

for (ifp = ifnet; n > 0 && 0 != ifp; ifp = ifp->int_next) {
if (ifp->int_rip_sock >= 0
&& FD_ISSET(ifp->int_rip_sock, ibitsp)) {
read_rip(ifp->int_rip_sock, ifp);
n--;
}
}
}
}

/* ARGSUSED */
void
sigalrm(int sig)
{
/* Historically, SIGALRM would cause the daemon to check for
* new and broken interfaces.
*/
ifinit_timer.tv_sec = now.tv_sec;
trace_act("SIGALRM\n"); /* XXX signal race */
}

/* watch for fatal signals */
void
sigterm(int sig)
{
stopint = sig;
(void)signal(sig, SIG_DFL); /* catch it only once */
}

void
fix_select(void)
{
struct interface *ifp;

sock_max = 0;

if (sock_max <= rt_sock)
sock_max = rt_sock+1;
if (rip_sock >= 0 && sock_max <= rip_sock)
sock_max = rip_sock+1;
for (ifp = ifnet; 0 != ifp; ifp = ifp->int_next) {
if (ifp->int_rip_sock >= 0 && sock_max <= ifp->int_rip_sock)
sock_max = ifp->int_rip_sock+1;
}
if (rdisc_sock >= 0 && sock_max <= rdisc_sock)
sock_max = rdisc_sock+1;

if (fdbitsp)
free(fdbitsp);
fdbitsp = (fd_set *)calloc(howmany(sock_max, NFDBITS),
sizeof(fd_mask));
if (fdbitsp == NULL)
err(1, "calloc");

FD_SET(rt_sock, fdbitsp);
if (rip_sock >= 0)
FD_SET(rip_sock, fdbitsp);
for (ifp = ifnet; 0 != ifp; ifp = ifp->int_next) {
if (ifp->int_rip_sock >= 0)
FD_SET(ifp->int_rip_sock, fdbitsp);
}
if (rdisc_sock >= 0)
FD_SET(rdisc_sock, fdbitsp);
}

void
fix_sock(int sock,
char *name)
{
int on;
#define MIN_SOCKBUF (4*1024)
static int rbuf;

if (fcntl(sock, F_SETFL, O_NONBLOCK) == -1)
logbad(1, "fcntl(%s) O_NONBLOCK: %s",
name, strerror(errno));
on = 1;
if (setsockopt(sock, SOL_SOCKET,SO_BROADCAST,
&on,sizeof(on)) < 0)
msglog("setsockopt(%s,SO_BROADCAST): %s",
name, strerror(errno));
if (rbuf >= MIN_SOCKBUF) {
if (setsockopt(sock, SOL_SOCKET, SO_RCVBUF,
&rbuf, sizeof(rbuf)) < 0)
msglog("setsockopt(%s,SO_RCVBUF=%d): %s",
name, rbuf, strerror(errno));
} else {
for (rbuf = 60*1024; ; rbuf -= 4096) {
if (setsockopt(sock, SOL_SOCKET, SO_RCVBUF,
&rbuf, sizeof(rbuf)) == 0) {
trace_act("RCVBUF=%d\n", rbuf);
break;
}
if (rbuf < MIN_SOCKBUF) {
msglog("setsockopt(%s,SO_RCVBUF = %d): %s",
name, rbuf, strerror(errno));
break;
}
}
}
}

/* get a rip socket
*/
static int /* <0 or file descriptor */
get_rip_sock(naddr addr,
int serious) /* 1=failure to bind is serious */
{
struct sockaddr_in sin;
unsigned char ttl;
int s;

if ((s = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
BADERR(1,"rip_sock = socket()");

bzero(&sin,sizeof(sin));
#ifdef _HAVE_SIN_LEN
sin.sin_len = sizeof(sin);
#endif
sin.sin_family = AF_INET;
sin.sin_port = htons(RIP_PORT);
sin.sin_addr.s_addr = addr;
if (bind(s, (struct sockaddr *)&sin,sizeof(sin)) < 0) {
if (serious)
BADERR(errno != EADDRINUSE, "bind(rip_sock)");
return -1;
}
fix_sock(s,"rip_sock");

ttl = 1;
if (setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL,
&ttl, sizeof(ttl)) < 0)
DBGERR(1,"rip_sock setsockopt(IP_MULTICAST_TTL)");

return s;
}

/* turn off main RIP socket */
void
rip_off(void)
{
struct interface *ifp;
naddr addr;

if (rip_sock >= 0 && !mhome) {
trace_act("turn off RIP\n");

(void)close(rip_sock);
rip_sock = -1;

/* get non-broadcast sockets to listen to queries.
*/
for (ifp = ifnet; ifp != 0; ifp = ifp->int_next) {
if (ifp->int_rip_sock < 0
&& !(ifp->int_state & IS_ALIAS)) {
addr = ((ifp->int_if_flags & IFF_POINTOPOINT)
? ifp->int_dstaddr
: ifp->int_addr);
ifp->int_rip_sock = get_rip_sock(addr, 0);
}
}

fix_select();

age(0);
}
}

/* turn on RIP multicast input via an interface
*/
static void
rip_mcast_on(struct interface *ifp)
{
struct ip_mreq m;

if (!IS_RIP_IN_OFF(ifp->int_state)
&& (ifp->int_if_flags & IFF_MULTICAST)
#ifdef MCAST_PPP_BUG
&& !(ifp->int_if_flags & IFF_POINTOPOINT)
#endif
&& !(ifp->int_state & IS_ALIAS)) {
m.imr_multiaddr.s_addr = htonl(INADDR_RIP_GROUP);
m.imr_interface.s_addr = ((ifp->int_if_flags & IFF_POINTOPOINT)
? ifp->int_dstaddr
: ifp->int_addr);
if (setsockopt(rip_sock,IPPROTO_IP, IP_ADD_MEMBERSHIP,
&m, sizeof(m)) < 0)
LOGERR("setsockopt(IP_ADD_MEMBERSHIP RIP)");
}
}

/* Prepare socket used for RIP.
*/
void
rip_on(struct interface *ifp)
{
/* If the main RIP socket is already alive, only start receiving
* multicasts for this interface.
*/
if (rip_sock >= 0) {
if (ifp != 0)
rip_mcast_on(ifp);
return;
}

/* If the main RIP socket is off, and it makes sense to turn it on,
* turn it on for all of the interfaces.
*/
if (rip_interfaces > 0 && !rdisc_ok) {
trace_act("turn on RIP\n");

/* Close all of the query sockets so that we can open
* the main socket. SO_REUSEPORT is not a solution,
* since that would let two daemons bind to the broadcast
* socket.
*/
for (ifp = ifnet; ifp != 0; ifp = ifp->int_next) {
if (ifp->int_rip_sock >= 0) {
(void)close(ifp->int_rip_sock);
ifp->int_rip_sock = -1;
}
}

rip_sock = get_rip_sock(INADDR_ANY, 1);
rip_sock_mcast = 0;

/* Do not advertise anything until we have heard something
*/
if (next_bcast.tv_sec < now.tv_sec+MIN_WAITTIME)
next_bcast.tv_sec = now.tv_sec+MIN_WAITTIME;

for (ifp = ifnet; ifp != 0; ifp = ifp->int_next) {
if (!IS_RIP_IN_OFF(ifp->int_state))
ifp->int_state &= ~IS_RIP_QUERIED;
rip_mcast_on(ifp);
}

ifinit_timer.tv_sec = now.tv_sec;

fix_select();

} else if (ifp != 0
&& ifp->int_rip_sock < 0
&& !(ifp->int_state & IS_ALIAS)) {
/* RIP is off, so ensure there are sockets on which
* to listen for queries.
*/
ifp->int_rip_sock = get_rip_sock(ifp->int_addr, 0);

fix_select();
}
}

/* die if malloc(3) fails
*/
void *
rtmalloc(size_t size,
char *msg)
{
void *p = malloc(size);
if (p == 0)
logbad(1,"malloc() failed in %s", msg);
return p;
}

/* get a random instant in an interval
*/
void
intvl_random(struct timeval *tp, /* put value here */
u_long lo, /* value is after this second */
u_long hi) /* and before this */
{
tp->tv_sec = (time_t)(hi == lo
? lo
: (lo + arc4random() % ((1 + hi - lo))));
tp->tv_usec = arc4random() % 1000000;
}

void
timevaladd(struct timeval *t1,
struct timeval *t2)
{

t1->tv_sec += t2->tv_sec;
if ((t1->tv_usec += t2->tv_usec) > 1000000) {
t1->tv_sec++;
t1->tv_usec -= 1000000;
}
}

/* t1 = t2 - t3
*/
static void
timevalsub(struct timeval *t1,
struct timeval *t2,
struct timeval *t3)
{
t1->tv_sec = t2->tv_sec - t3->tv_sec;
if ((t1->tv_usec = t2->tv_usec - t3->tv_usec) < 0) {
t1->tv_sec--;
t1->tv_usec += 1000000;
}
}

void
msglog(char *p, ...)
{
va_list args;

trace_flush();

va_start(args, p);
vsyslog(LOG_ERR, p, args);
va_end(args);

if (ftrace != 0) {
if (ftrace == stdout)
(void)fputs("routed: ", ftrace);
va_start(args, p);
(void)vfprintf(ftrace, p, args);
va_end(args);
(void)fputc('\n', ftrace);
}
}

void
logbad(int dump, char *p, ...)
{
va_list args;

trace_flush();

va_start(args, p);
vsyslog(LOG_ERR, p, args);
va_end(args);

(void)fputs("routed: ", stderr);
va_start(args, p);
(void)vfprintf(stderr, p, args);
va_end(args);
(void)fputs("; giving up\n",stderr);
(void)fflush(stderr);

if (dump)
abort();
exit(1);
}