Re: [RFC iproute2 1/1] ip: netns: add mounted state file for each netns

[Matteo Croce <mcroce@redhat.com>]

On Fri, Jun 28, 2019 at 7:06 PM Matteo Croce <mcroce@redhat.com> wrote:
>
> On Fri, Jun 28, 2019 at 6:27 PM David Howells <dhowells@redhat.com> wrote:
> >
> > Nicolas Dichtel <nicolas.dichtel@6wind.com> wrote:
> >
> > > David Howells was working on a mount notification mechanism:
> > > https://lwn.net/Articles/760714/
> > > https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=notifications
> > >
> > > I don't know what is the status of this series.
> >
> > It's still alive.  I just posted a new version on it.  I'm hoping, possibly
> > futiley, to get it in in this merge window.
> >
> > David
>
> Hi all,
>
> this could cause a clash if I create a netns with name ending with .mounted.
>
> $ sudo ip/ip netns add ns1.mounted
> $ sudo ip/ip netns add ns1
> Cannot create namespace file "/var/run/netns/ns1.mounted": File exists
> Cannot remove namespace file "/var/run/netns/ns1.mounted": Device or
> resource busy
>
> If you want to go along this road, please either:
> - disallow netns creation with names ending with .mounted
> - or properly document it in the manpage
>
> Regards,
> --
> Matteo Croce
> per aspera ad upstream

BTW, this breaks the namespace listing:

# ip netns add test
# ip netns list
Error: Peer netns reference is invalid.
Error: Peer netns reference is invalid.
test.mounted
test

A better choice IMHO could be to create a temporary file before the
placeholder, and delete it after the bind mount, so an inotify watcher
can listen for the delete event.
For example, when creating the namespace "foo":

- create /var/run/netns/.foo.mounting
- create /var/run/netns/foo
- bind mount from /proc/.. to /var/run/netns/foo
- remove /var/run/netns/.foo.mounting

and exclude .*.mounting from the netns listing

Or, announce netns creation/deletion in some other way (dbus?).

Regards,
-- 
Matteo Croce
per aspera ad upstream