From owner-freebsd-current  Tue Jun 16 17:33:40 1998
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To: Terry Lambert <tlambert@primenet.com>
cc: current@FreeBSD.ORG
Subject: Re: Bogus errno twiddling by lstat... 
In-reply-to: Your message of "Tue, 16 Jun 1998 23:55:32 GMT."
             <199806162355.QAA06852@usr02.primenet.com> 
Date: Wed, 17 Jun 1998 08:32:56 +0800
From: Peter Wemm <peter@netplex.com.au>
Sender: owner-freebsd-current@FreeBSD.ORG
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Terry Lambert wrote:
> Try the following program:
> 
> 	#include <sys/types.h>
> 	#include <sys/stat.h>
> 	#include <errno.h>
> 
> 
> 	main()
> 	{
> 		struct stat     sb;
> 
> 		errno = 0;
> 		printf( "lstat(fred) = %d\n", lstat( "fred", &sb));
> 		perror( "lstat");
> 	}
> 
> If "fred" exists in the current directory, you would expect that errno
> would not have been modified, and the output will be:
> 
> 	lstat(fred) = 0
> 	lstat: Undefined error: 0
> 
> However, what comes out instead is:
> 
> 	lstat(fred) = 0
> 	lstat: No such file or directory
> 
> Indicating that lstat is diddling errno when it shouldn't be.

1: This is a classic programming error.. You're not really supposed to be 
looking at the value of errno except right after a -1 return from 
something.

2: the no such file or directory is actually stdio calling malloc, which 
is doing a readlink on /etc/malloc.conf, which probably doesn't exist.

3: You're calling stdio (ie: printf) *after* lstat() so you've gotten 
what's coming to you. :-)  You're initializing the entire stdio system 
after calling lseek().  It's stdio that's leaking the errno.

Cheers,
-Peter



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