From owner-cvs-all  Tue Mar 21 20:31:54 2000
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Date: Tue, 21 Mar 2000 23:30:14 -0500 (EST)
From: Brian Fundakowski Feldman <green@FreeBSD.org>
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To: Brian Somers <brian@FreeBSD.org>
Cc: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject: Re: cvs commit: src/usr.sbin/ppp exec.c
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On Tue, 21 Mar 2000, Brian Somers wrote:

>   FWIW:
>     I tried to implement this by doing a pipe(), setting the
>     write desciptors close-on-exec flag in the child and writing
>     errno to the descriptor if the exec() fails.  The parent can
>     then ``if (read()) got errno else exec worked''.
>   
>     This didn't work though - the child could write() to fd[1] on
>     exec failure, but the parent got 0 trying to read() from fd[0] !
>     Is this a bug in execve() ?

I didn't do anything to change the close-on-exec-ness, but this test case
here works fine for me:

{"/home/green"}$ ./bar
Poppa here, how's it going, son?
Hey, dad!  Lemme exec something impossible.
Oh, so it's "4186" you say?

bar.c:
#include <err.h>
#include <stdio.h>
#include <unistd.h>

int
main() {
	int pipes[2];
	int error;
	char data[sizeof(int)];
	char *const impossible[] = { "/", NULL };

	error = pipe(pipes);
	if (error != 0)
		err(1, "pipe");
	switch (fork()) {
	case 0:
		printf("Poppa here, how's it going, son?\n");
		if (write(pipes[0], "", 1) != 1)
			err(1, "parent write");
		if (read(pipes[0], data, sizeof(data)) != sizeof(data))
			err(1, "parent read");
		printf("Oh, so it's \"%d\" you say?\n", *(int *)data);
		exit(0);
	case -1:
		err(1, "fork");
	default:
		if (read(pipes[1], data, 1) != 1)
			err(1, "child read");
		printf("Hey, dad!  Lemme exec something impossible.\n");
		(void)execve(*impossible, impossible, NULL);
		*(int *)data = 4186;
		if (write(pipes[1], data, sizeof(data)) != sizeof(data))
			err(1, "child write");
		exit(0);
	}
}

--
 Brian Fundakowski Feldman           \  FreeBSD: The Power to Serve!  /
 green@FreeBSD.org                    `------------------------------'



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