Re: RFC: renameat(): Add a RENAME_REMOVE flag to unlink hardlinks

[Al Viro <viro@ZenIV.linux.org.uk>]

On Fri, Nov 21, 2014 at 05:51:23PM -0800, Andy Lutomirski wrote:
> On Fri, Nov 21, 2014 at 5:50 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> > On Sat, Nov 22, 2014 at 01:29:05AM +0000, Pádraig Brady wrote:
> >
> >> > I assume that VFS can handle this correctly if it wants to.
> >>
> >> I was assuming there was a way to distinguish directory entries,
> >> and that's what should be checked first, which is what my
> >> psuedo code patch attempted to show.
> >
> > There isn't, in general.  Sure, if you get the same struct dentry * from
> > both lookups, it's the same one.  But it's not guaranteed to be true on
> > every fs out there if those are non-directories (and for directories there's
> > no multiple hardlinks in the first place).
> 
> Does that mean that the current behavior is inconsistent between filesystems.

No.  You can always check that they point to the same inode.  Which is
precisely what "links to the same file" is about, and which is why rename(2)
had that semantics since way back.  _That_ is easy condition to check.
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