#include <u.h>#include <libc.h>#include <bio.h>#include "awk.h" #define MAXFORKS	20#define NSYSFILE	3#define	tst(a,b)	(mode == OREAD? (b) : (a))#define	RDR	0#define	WTR	1 struct a_fork {	short	done;	short	fd;	int	pid;	char status[128];};static struct a_fork the_fork[MAXFORKS]; Biobuf*popen(char *cmd, int mode){	int p[2];	int myside, hisside, pid;	int i, ind; 	for (ind = 0; ind < MAXFORKS; ind++)		if (the_fork[ind].pid == 0)			break;	if (ind == MAXFORKS)		return nil;	if(pipe(p) < 0)		return nil;	myside = tst(p[WTR], p[RDR]);	hisside = tst(p[RDR], p[WTR]);	switch (pid = fork()) {	case -1:		return nil;	case 0:		/* myside and hisside reverse roles in child */		close(myside);		dup(hisside, tst(0, 1));		for (i=NSYSFILE; i<FOPEN_MAX; i++)			close(i);		execl("/bin/rc", "rc", "-c", cmd, nil);		exits("exec failed");	default:		the_fork[ind].pid = pid;		the_fork[ind].fd = myside;		the_fork[ind].done = 0;		close(hisside);		return(Bfdopen(myside, mode));	}} intpclose(Biobuf *ptr){	int f, r, ind;	Waitmsg *status; 	f = Bfildes(ptr);	Bterm(ptr);	for (ind = 0; ind < MAXFORKS; ind++)		if (the_fork[ind].fd == f && the_fork[ind].pid != 0)			break;	if (ind == MAXFORKS)		return -1;	if (!the_fork[ind].done) {		do {			if((status = wait()) == nil)				r = -1;			else				r = status->pid;			for (f = 0; f < MAXFORKS; f++) {				if (r == the_fork[f].pid) {					the_fork[f].done = 1;					strecpy(the_fork[f].status, the_fork[f].status+512, status->msg);					break;				}			}			free(status);		} while(r != the_fork[ind].pid && r != -1);		if(r == -1)			strcpy(the_fork[ind].status, "No loved ones to wait for");	}	the_fork[ind].pid = 0;	if(the_fork[ind].status[0] != '\0')		return 1;	return 0;}