Re: [Qemu-devel] [PATCH 1/1] qemu-nbd: add the option to use pre-created server socket

["Daniel P. Berrange" <berrange@redhat.com>]

On Thu, Sep 29, 2016 at 02:18:54PM +0200, Paolo Bonzini wrote:
> 
> 
> On 29/09/2016 13:13, Daniel P. Berrange wrote:
> > On Thu, Sep 29, 2016 at 02:02:15PM +0300, Denis V. Lunev wrote:
> >> From: Denis Plotnikov <dplotnikov@virtuozzo.com>
> >>
> >> Originally NBD server socket was created by qemu-nbd code. This leads to
> >> the race when the management layer starts qemu-nbd server and allows a
> >> client to connect to the server. In this case there is a possibility that
> >> qemu-nbd does not open listening server socket yet. Creating listening
> >> socket before starting of qemu-ndb and passing socket fd via command line
> >> solves this issue completely.
> > 
> > FWIW, this could be solved in qemu-nbd itself if we had a general
> > ability to request "daemon" mode - currently it only daemonizes
> > if attaching to a nbd block device.
> > 
> > The key would be that qemu-nbd would open the listening socket
> > before daemonizing. Thus when the mgmt application spawned
> > qemu-nbd in daemon mode, it can be sure that the listener
> > socket is present when waitpid() completes.
> 
> This is 100% true, but I find daemonization to be a hack, so file
> descriptor passing has its place.
> 
> Still, I'd prefer to have a --socket-activation option which uses the
> systemd socket activation protocol.  The systemd protocol can be
> implemented easily by any management layer.

That's a nice idea - system socket activation is pretty simple todo


Regards,
Daniel
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