#define _GNU_SOURCE

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <utmp.h>
#include <ctype.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <time.h>
#include <errno.h>


#ifdef __linux__
#include <linux/vt.h>
#include <sys/ioctl.h>
#endif

#ifndef MIN
#define	MIN(a,b) (((a)<(b))?(a):(b))
#endif


#define LOGIN "/bin/login"
#define KILLTIME 5
#define CONFFILE "/etc/conlogind.conf"
#define PIDFILE  "/var/run/conlogind.pid"

struct conlogin {
	char *tty;
	char *line;
	char id[3];
	pid_t pid;
	unsigned short vt;
};

extern int dotermreset(const char *tty);

struct conlogin *conlogins;
int nvcons = 0;
sig_atomic_t doquit = 0;

void *xmalloc(size_t size){
	void *p;
	p = malloc(size);
	if(p==NULL){
		fprintf(stderr,"malloc() failure\n");
		exit(EXIT_FAILURE);
	}
	return(p);
}

struct conlogin* setup(int n){
	struct conlogin *conlogins;
	struct conlogin *l;
	int i;
	char buf[16];
	conlogins = xmalloc(sizeof(struct conlogin)*n);
	for(i=0;i<n;i++){ 
		l = &conlogins[i];
		l->vt = i + 1;
		snprintf(buf,sizeof(buf),"/dev/vc/%i",l->vt);
		l->tty = xmalloc(strlen(buf)+1);
		strcpy(l->tty,buf);
		l->line = l->tty + 5; /* "/dev/" */
		snprintf(l->id,sizeof(l->id),"%02d",l->vt);
		l->pid = 0;
	}
	return(conlogins);
}

void write_utmp_wtmp(struct conlogin *l, short int type){
	struct utmp utmp;
	memset(&utmp,'\0',sizeof(utmp));
	strncpy(utmp.ut_id,l->id,MIN(sizeof(utmp.ut_id),sizeof(l->id)));
	strncpy(utmp.ut_line,l->line,UT_LINESIZE);
	utmp.ut_type = type;
	utmp.ut_pid = l->pid;
	utmp.ut_time = time(NULL);
	setutent();
	pututline(&utmp);
	endutent();
	updwtmp(_PATH_WTMP,&utmp);
}

void startlogin(struct conlogin *l){
	pid_t pid;
	int i;
	int fd;
	char *argv[] = { LOGIN, NULL };
	
	pid = fork();
	if(pid > 0) {
		l->pid = pid;
		write_utmp_wtmp(l,LOGIN_PROCESS);
	} else if(pid == 0) {
		for(i=0;i<NSIG;i++) signal(i,SIG_DFL);
		setsid();
		fd = open(l->tty,O_RDWR);
		if(fd >= 0) {
			for(i=2;i>=0;i--){
				close(i);
				dup(fd);
			}
			close(fd);
			execv(argv[0],argv);
			perror(LOGIN);
		} else {
			perror("open");
		}
		sleep(5); /* So we don't get runaway respawning */
		_exit(127);
	} else {
		perror("fork");
	}
}

void endlogin(struct conlogin *l){
	write_utmp_wtmp(l,DEAD_PROCESS);
	l->pid = 0;
	if(!doquit || l->vt != 1 )
		dotermreset(l->tty); /* Clean up the terminal */
}

void sendkill(int n){
	int serrno = errno;
	int i;
	for(i=0;i<nvcons;i++)
		if(conlogins[i].pid)
			kill(conlogins[i].pid,SIGKILL);
	signal(SIGALRM,SIG_DFL);
	errno = serrno;
}

void sigterm(int n){
	int serrno = errno;
	int i;
	doquit = 1;
	for(i=0;i<nvcons;i++)
		if(conlogins[i].pid)
			kill(conlogins[i].pid,SIGHUP);
	signal(SIGALRM,sendkill);
	alarm(KILLTIME);
	errno = serrno;
}

int main(int argc,char * argv[]){
	int status;
	pid_t pid;
	int i;
	FILE *fp;
	int thiscon;
	
	if(argc < 2) {
		if((fp = fopen(CONFFILE,"r"))){
			fscanf(fp,"%i",&nvcons);
			fclose(fp);
		}
	} else {
		nvcons = strtol(argv[1],NULL,0);
	}
	
	if(nvcons <= 0)
		nvcons = 1;
			
	conlogins = setup(nvcons);

	signal(SIGTERM,sigterm);

	pid = fork();
	if(pid==-1){
		perror("fork");
		exit(EXIT_FAILURE);
	}
	if(pid > 0){ /* Parent */
		if((fp = fopen(PIDFILE,"w"))){
			fprintf(fp,"%i\n",pid);
			fclose(fp);
		}
		exit(EXIT_SUCCESS);
	}
	/* Child */
	setsid();
	chdir("/");
	/* We want stdout to spam to when something goes bad, but no stdin */
	close(0);
	open("/dev/null",O_RDWR);

	for(i=0;i<nvcons;i++)
		startlogin(&conlogins[i]);

	for(;;){
		pid = waitpid(WAIT_ANY,&status,0);
		if(pid <= 0) continue;
		for(i=0;i<nvcons;i++) if(conlogins[i].pid == pid) break;
		if(i==nvcons) continue;
		thiscon = i;
		endlogin(&conlogins[thiscon]);
		if(doquit){
			for(i=0;i<nvcons;i++)
				if(conlogins[i].pid>0)
					break;
			if(i<nvcons)
				continue; /* don't start a new one */
			else
				break; /* all gone! */
		}
		startlogin(&conlogins[thiscon]);
	}
	unlink(PIDFILE);
	return(EXIT_SUCCESS);
}