Re: [RFC][PATCH 0/9] Make containers kernel objects

[David Howells <dhowells@redhat.com>]

Colin Walters <walters@verbum.org> wrote:

> Why not drop the upcall model in favor of having userspace monitor events
> via a (more efficient) protocol and react to them on its own?

 (1) That's not necessarily more efficient.  You now have the overhead of a
     permanently running userspace daemon in every relevant namespace
     combination.

 (2) You then have to work out how to route to the appropriate daemon.

> It's just generally more flexible

Actually, it's less flexible.  You can't easily get at the caller's
namespaces.

> and avoids all of those issues like replicating the seccomp configuration,
> etc.

So does my container implementation.

> Something like inotify/signalfd could be a precedent around having a read()/poll()able
> fd.  /proc/keys-requests ?
>
> Then if you create a new user namespace, and open /proc/keys-requests, the
> kernel will always write to that instead of calling /sbin/request-key.

That's not good enough.  You're basically making it one daemon per user
namespace and ignoring all the other namespaces.

[Also note that the kernel would have to paste a temporary authorisation key
 into the daemon's session keyring for each key that requires instantiation].

David