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From: arisawa <arisawa@ar.aichi-u.ac.jp>
In-Reply-To: <44900c0d4896622fa8a9411b05efe730@brasstown.quanstro.net>
Date: Mon, 26 Jan 2015 20:47:58 +0900
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Message-Id: <7A132462-4747-471A-A4BF-D9381E38A4EA@ar.aichi-u.ac.jp>
References: <E9D002A0-CF5A-4059-96F9-9365F67D119B@ar.aichi-u.ac.jp>
	<0F748B67-FB11-464C-84FA-66B4E0B29918@9.offblast.org>
	<44900c0d4896622fa8a9411b05efe730@brasstown.quanstro.net>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Subject: Re: [9fans] protection against resource exhaustion
Topicbox-Message-UUID: 3b7a3588-ead9-11e9-9d60-3106f5b1d025

Hello,

I have been playing the following program.
I tried on official plan9, 9front, and 9atom.
none of them showed messages that come from:
		sysfatal("fork: %r=E2=80=9D);
		sysfatal("exec: %r");
I suspect that
	fork()
does not return -1 even if it failed in creating new process.

Be ware this program may cause system panic.

#include <u.h>
#include <libc.h>
#define ERRLEN 256

static int
waitfor(int pid, char *msg)
{
	Waitmsg *w;
	while((w =3D wait()) !=3D nil){
		if(w->pid =3D=3D pid){
			strncpy(msg, w->msg, ERRMAX);
			free(w);
			return 0;
		}
		free(w);
	}
	return -1;
}

int
run(char *path, char *cmd)
{
	int pid;
	int status;
	int n;
	char *args[32];
	char msg[ERRLEN];

	n =3D tokenize(cmd, args, 32);
	args[n] =3D nil;

	switch(pid =3D fork()) {/* assign =3D */
	case -1:
		sysfatal("fork: %r");
	case 0:
		close(0);
		exec(path, args);
		sysfatal("exec: %r");
	default:
		break;
	}
	status =3D waitfor(pid, msg);
	if(status < 0){
		werrstr("waitfor: %r");
		return -1;
	}
	return 0;
}

void main(int argc, char *argv[])
{	char *e;
	int n;
	int m =3D 100;
	char buf[32];
	ARGBEGIN{
	case 'm':	m =3D atoi(ARGF());
		break;
	default: sysfatal("usage");
	}ARGEND

	if(argv[0])
		n =3D atoi(argv[0]);
	else
		n =3D 0;
	if(n =3D=3D m)
		sysfatal("stop");

	print("%d\n",n);
	snprint(buf,sizeof(buf),"8.out -m %d %d",m,n + 1);
	run("./8.out", buf);
	exits(nil);
}