On Wed, Jun 24, 2026 at 07:53:53PM -0400, John Ericson wrote:

I wanted to discuss a bit about each type of namespace to indicate that
this is a concept I think works across the board --- it wouldn't be such
a good solution for the process spawning API if it was only applicable
to some but not all namespace types. But the truth is that I have
thought about the FS cases the most, as I think you have picked up on.

If there is interest in landing

  1. null CWD
  2. null root fs
  3. null mount namespace

in isolation, and then returning to the other namespaces to iron out
their details, that would be fantastic. It would be much nicer for me to
get some momentum that way, without having to design everything all at
once first before getting to implement anything.

Please, start with explaining what, in your opinion, a mount namespace _is_,
and where does "mount X is attached at path P relative to mount Y" belong.

What's the fundamental difference between CWD and any open descriptor for
a directory?  Why does it make sense to ban the former, but allow the
equivalents done via the latter?