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 02:02:15PM +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.

Regards,
Daniel
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