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Date: Sat, 11 Dec 2021 18:55:49 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: Eugene Grosbein <eugen@grosbein.net>
Cc: Gleb Popov <arrowd@freebsd.org>, "Daniel O'Connor" <darius@dons.net.au>,
        freebsd-hackers <freebsd-hackers@freebsd.org>
Subject: Re: What to use in place of abstract unix sockets?
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On Sat, Dec 11, 2021 at 11:20:33PM +0700, Eugene Grosbein wrote:
> 11.12.2021 16:59, Gleb Popov wrote:
> 
> > EXDEV: Cross-device link
> > 
> > This might be because the chroot's target directory is an nullfs mount. Am
> > I right that it isn't possible to create hard links that span nullfs mount
> > points?
> 
> It is not possible to create hard links for source and destination directories
> with different st_dev values as per stat(2), this includes nullfs,
> each of which has its own st_dev id.

The VOP_UNP_BIND() and VOP_UNP_CONNECT() vops are bypassed to the lower
fs. It means that if you bind(2) or connect(2) on unix domain socket
that is visible through nullfs mount, effectively you are doing the bind
or connect operation on the lower filesystem.

That said, implementing 'abstract' unix socket addresses would be nice.