Writing to A NON-Existing File in "C"

[Stephen J. Friedl]

In article <14020030 at hpisod2.HP.COM>, decot at 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 at vsi.com   {backbones}!vsi.com!friedl    attmail!vsi!friedl