Path: utzoo!mnetor!uunet!vsi!friedl
From: friedl@vsi.UUCP (Stephen J. Friedl)
Newsgroups: comp.unix.wizards
Subject: Re: Writing to A NON-Existing File in "C"
Message-ID: <574@vsi.UUCP>
Date: 20 Apr 88 15:40:19 GMT
References: <9654@jplgodo.UUCP> <14020030@hpisod2.HP.COM>
Organization: V-Systems, Inc. -- Santa Ana, CA
Lines: 22
Summary: *PLEASE* don't use access(2)

In article <14020030@hpisod2.HP.COM>, decot@hpisod2.HP.COM (Dave Decot) writes:
> Uh...I think a file's existence is independent of your user-id.
> 
> It's perfectly acceptable to use access(2) the F_OK (0) value of amode
> it to determine whether files exist.  Such calls succeed exactly when
> calls to stat(2) succeed.

Not quite -- parent directory modes will get in the way.  In the
case where the real uid has no permission in a parent directory
component of a file but but the effective uid does, stat(2)
succeeds and access(2) fails.  So,

 	access("/tmp/secret.dir/open.file", 0);
and
 	stat("/tmp/secret.dir/open.file", &stbuf);

are not guaranteed to return the same values if /tmp/secret.dir
is available to the set-user-id but not to me.

-- 
Steve Friedl       V-Systems, Inc.      Resident access(2) basher
friedl@vsi.com   {backbones}!vsi.com!friedl    attmail!vsi!friedl