Re: [Virtio-fs] [External] Re: [RFC PATCH 0/9] Support for Virtio-fs daemon crash reconnection

[Vivek Goyal <vgoyal@redhat.com>]

On Mon, Mar 22, 2021 at 11:00:52AM +0000, Stefan Hajnoczi wrote:
> On Wed, Mar 17, 2021 at 08:32:31PM +0800, Jiachen Zhang wrote:
> > On Wed, Mar 17, 2021 at 6:05 PM Stefan Hajnoczi <stefanha@redhat.com> wrote:
> > > On Fri, Dec 18, 2020 at 05:39:34PM +0800, Jiachen Zhang wrote:
> > I agreed with you that a virtiofsd must be launched by a software like
> > systemd. So we are planning to define more generic persist/restore
> > interfaces (callbacks). Then anyone can implement their own persist/restore
> > callbacks to store states to proper places.  And I think in the next
> > version we will implement default callbacks for the interfaces. Instead of
> > vhost-user messages, systemd's sd_notify(3) will be the default method for
> > storing fds, and several tmpfs files can be the default place to store the
> > shm regions.
> 
> Okay, great!
> 
> I was thinking about how to make the crash recovery mechanism reusable
> as a C library or Rust crate. The mechanism is a combination of:
> 1. sd_listen_fds(3) for restoring the fds on restart.
> 2. sd_notify(3) for storing the fds.
> 3. memfd or tmpfs for storing state (could be mmapped).
> 
> I'm not sure if there is enough common behavior to create a reusable API
> or if this is quite application-specific.

I am wondering what will happen for use cases where virtiofsd is running
inside a container (with no systemd inside containers).

Do container managers offer systemd like services to save and restore
state.

Vivek