Re: I am confused about the configure rename managing hardlinks test.

[John E. Malmberg]

On 9/29/2017 6:43 PM, Eric Blake wrote:
> On 09/29/2017 06:13 PM, John E. Malmberg wrote:
> > Hello,
> >
> > I am confused about the rename managing hardlinks test.
> >
> > It starts out with conftest.f as an empty file and conftest.fl as a hard
> > link to conftest.f.
> >
> > Step 1:
> >      rename ("conftest.f", "conftest.f1")
> >
> > I would expect after a success, conftest.f would no longer exist, only
> > conftest.f1.
>
> Sadly, your expectations are contrary to the POSIX requirements, that if
> two (possibly different hard-links) names point to the same inode, then
> rename() is a no-op rather than removing one of the two names.  This
> behavior is historical, even though it violates the principle of least
> surprise, so the kernel can't really change it, and GNU coreutils 'mv'
> has to go to great lengths to work around this shortcoming in the
> syscall specification.

I suspected something like that.

I have read and re-read:
http://pubs.opengroup.org/onlinepubs/9699919799/functions/rename.html

And I do not see anything in that text that states the behavior would be 
a noop when the source and destination links to the same file.

> The new Linux renameat2() syscall would have to add a new RENAME_ flag
> if we wanted any saner behavior (although there has also been a recent
> report that one of the BSD's wrote a broken rename() syscall that
> behaves sanely by default).  But until someone implements that, and we
> can rely on it, then you must assume that "conftest.f" still exists
> after this no-op call.

The OpenVMS rename() removes the "conftest.f" and creates a "conftest.f1;2"

> > Step 2:
> >      unlink ("conftest.f1")
> >
> > Now I would expect confest.f1 to not exist after this.
>
> Correct.

Except on OpenVMS of course, it removes "conftest.f1;" leaving the 
original "conftest.f1".

> > Step 3 is what confuses me.
> >
> >     rename("conftest.f", "conftest.f") which is expected to work.
> >
> > How can this succeed if "conftest.f" was removed in step 1?
>
> Because it wasn't removed in step 1.

Ok, now I need to do with the OpenVMS specific code.

Thanks,
-John