Re: [PATCH 0/5] Introduce 'yank' oob qmp command to recover from hanging qemu

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Daniel P. Berrangé (berrange@redhat.com) wrote:
> On Wed, May 13, 2020 at 01:56:24PM +0100, Dr. David Alan Gilbert wrote:
> > * Kevin Wolf (kwolf@redhat.com) wrote:
> > > I guess it would be nice to have a single namespace for everything in
> > > QEMU, but the reality is that we have a few separate ones. As long as we
> > > consistently add a prefix that identifies the namespace in question, I
> > > think that would work.
> > 
> > > This means that if we're using node-name to identify the NBD connection,
> > > the namespace should be 'block' rather than 'nbd'.
> > > 
> > > One more thing to consider is, what if a single object has multiple
> > > connections? In the case of node-names, we have a limited set of allowed
> > > characters, so we can use one of the remaining characters as a separator
> > > and then suffix a counter. In other places, the identifier isn't
> > > restricted, so suffixing doesn't work. Maybe prefixing does, but it
> > > would have to be there from the beginning then.
> > 
> > Yeh I worry about whether on nbd if you can have multiple nbd
> > connections to one block device.
> 
> The kernel NBD driver now supports multiple parallel connections.
> QEMU hasn't implemented this in its NBD code yet, but I certainly
> see that being in scope for future.

It's not parallel for performance that worries me, it's more about
separateq connections for separate uses - e.g. if we're serving the same
read-only disk to multiple separate things.

Dave
 
> 
> Regards,
> Daniel
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Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK