Re: [PATCH 00/23] proc: Introduce /proc/namespaces/ directory to expose namespaces lineary

From: Andrei Vagin
Date: Tue Aug 04 2020 - 01:43:19 EST

On Thu, Jul 30, 2020 at 06:01:20PM +0300, Kirill Tkhai wrote:
> On 30.07.2020 17:34, Eric W. Biederman wrote:
> > Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> writes:
> >
> >> Currently, there is no a way to list or iterate all or subset of namespaces
> >> in the system. Some namespaces are exposed in /proc/[pid]/ns/ directories,
> >> but some also may be as open files, which are not attached to a process.
> >> When a namespace open fd is sent over unix socket and then closed, it is
> >> impossible to know whether the namespace exists or not.
> >>
> >> Also, even if namespace is exposed as attached to a process or as open file,
> >> iteration over /proc/*/ns/* or /proc/*/fd/* namespaces is not fast, because
> >> this multiplies at tasks and fds number.

Could you describe with more details when you need to iterate

There are three ways to hold namespaces.

* processes
* bind-mounts
* file descriptors

When CRIU dumps a container, it enumirates all processes, collects file
descriptors and mounts. This means that we will be able to collect all
namespaces, doesn't it?