Re: [RFC] Null Namespaces

[Al Viro]

On Wed, Jun 24, 2026 at 06:51:47PM -0400, John Ericson wrote:

> #### Null mount namespace
> 
> - requires:
> 
>   - null root file system: absolute paths don't work.
> 
>   - null current working directory: relative paths with traditional,
>     non-`*at` system calls (and `*at` ones using `AT_FDCWD`) don't work.
> 
> - All operations relating to the "ambient" mount tree don't work.
> 
> - `*at` operations with a file descriptor do work.

Huh?  The last bit looks contradicts the previous one - if you have
an opened directory in a mount from some namespace, those `*at` operations
with that descriptor *will* be seeing the mount tree of that namespace,
whatever the hell is "ambient" supposed to mean.  Either that, or you
will be exposing whatever's overmounted in that mount, which is a huge
can of worms.