/*  * This file is part of the UCB release of Plan 9. It is subject to the license * terms in the LICENSE file found in the top-level directory of this * distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No * part of the UCB release of Plan 9, including this file, may be copied, * modified, propagated, or distributed except according to the terms contained * in the LICENSE file. */ #include <stdlib.h>#include <stdio.h>#include <sys/types.h>#include <unistd.h>#include <sys/wait.h> #define MAXFORKS	20#define NSYSFILE	3#define	tst(a,b)	(*mode == 'r'? (b) : (a))#define	RDR	0#define	WTR	1 struct a_fork {	short	done;	short	fd;	int	pid;	int	status;};static struct a_fork the_fork[MAXFORKS]; FILE *popen(char *cmd, char *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 NULL;	if(pipe(p) < 0)		return NULL;	myside = tst(p[WTR], p[RDR]);	hisside = tst(p[RDR], p[WTR]);	switch (pid = fork()) {	case -1:		return NULL;	case 0:		/* myside and hisside reverse roles in child */		close(myside);		dup2(hisside, tst(0, 1));		for (i=NSYSFILE; i<FOPEN_MAX; i++)			close(i);		execl("/bin/ape/sh", "sh", "-c", cmd, NULL);		_exit(1);	default:		the_fork[ind].pid = pid;		the_fork[ind].fd = myside;		the_fork[ind].done = 0;		close(hisside);		return(fdopen(myside, mode));	}} intpclose(FILE *ptr){	int f, r, ind;	int status; 	f = fileno(ptr);	fclose(ptr);	for (ind = 0; ind < MAXFORKS; ind++)		if (the_fork[ind].fd == f && the_fork[ind].pid != 0)			break;	if (ind == MAXFORKS)		return 0;	if (!the_fork[ind].done) {		do {			r = wait(&status);			for (f = 0; f < MAXFORKS; f++)				if (the_fork[f].pid == r) {					the_fork[f].done = 1;					the_fork[f].status = status;					break;				}		} while(r != the_fork[ind].pid && r != -1);		the_fork[ind].status = r == -1 ? -1 : status;	}	the_fork[ind].pid = 0;	return (the_fork[ind].status);}