Re: Link count for directories

Adam Borowski
2020-08-24T22:23:14Z

On Mon, Aug 24, 2020 at 11:50:30PM +0200, Steve Keller wrote:
> Nikolay Borisov <nborisov@suse.com> wrote:
> > I have implemented it so it's not that big of a deal. However turns out
> > it has pretty steep requirements for backport because so far btrfs
> > always kept the link count of dirs to 1.

> > So how effective is such an optimisation to the software using it ?
>
> It's not only optimization like in find(1). As an old and long-time Unix
> user I'd also like that traditional behavior. It just feels more correct
> since if you do mkdir ./a ./b ./c ./d, you will actually see the 4 links
> to the current dir if you do ls -ai a b c d and the two links from . itself
> and from ..

It's just an implementation detail of sysvfs, and a case of
bug-compatibility. The link count of a directory is always 1 as btrfs,
ext4, xfs, etc -- none of them support directory hardlinks, unlike sysvfs.

So the proper value, as documented, is 1. Copying sysvfs behaviour is also
costly as you need to know the count of contents while statting parent.

Meow!
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