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

[Stefan Hajnoczi]

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.

Stefan

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