Hard Link

[dc0d32]

On ext file system in Linux, why can't we create hard links to directories?
What could be the reason?

thanks.

(Haven't tried with other FS or maybe it is with *NIX. No idea.)

[Colonel Kernel]

Hard links can have multiple "parents". If you're in a hard linked directory and type "cd ..", where should the new current directory be?

[dc0d32]

It's clear now. Thanks.

[Pype.Clicker]

Even if that "cd .." is managed (e.g. you keep the full path somewhere in the kernel), hard links to directories turn your filesystem (usually a tree) into a graph -- which may contain cycles.

/home: mkdir foo
/home/foo: ln /home bar
/home: find -type d
/home
/home/foo
/home/foo/bar
/home/foo/bar/foo
/home/foo/bar/foo/bar ...

that would break most directory-crawling software existing. Generally speaking, allowing hard links to directories while preventing cycles to appear require something looking like a mark-and-sweep garbage collector ... not the kind of thing you'll love to have in the kernel FS driver

(more about it in Tanenbaum books)

[Candy]

The only requirement is to check for the entire tree link to the top of the target location whether your item is in it. If not, you're not creating a cycle.

Of course, you have to add this to the move logic too.

[dc0d32]

The only requirement is to check for the entire tree link to the top of the target location whether your item is in it.

Is that even deterministic?