Re: [9fans] trying to understand how fork/pipe a filtering program

[rog@vitanuova.com]

i'd have thought that something like the following should work:

	int p[2], q[2], kid, pid;
	Image *img;

	if(pipe(p) < 0 || pipe(q) < 0)
		sysfatal("can't make a pipe: %r");
	kid = fork();
	switch(kid){
	case -1:
		sysfatal("can't fork: %r");
	default:
		close(p[0]);
		close(q[1]);
		if (writeimage(p[1], from, 0) < 0)
			fprint(2, "error writeimage\n");
		close(p[1]);
		img = readimage(display, q[0], 0);
		close(q[0]);
		/*
		 * we may have unknown children forked by a previous
		 * program (e.g., rc) that then execed us.
		 */
		while ((pid = waitpid()) != kid && pid != -1)
			continue;
		return img;
	case 0:
		dup(p[0], 0);
		dup(q[1], 1);
		close(p[1]);
		close(q[0]);
		execl("/bin/resample", "resample", "-x50%", (char *)nil);
		sysfatal("can't exec resample: %r");
	}