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


From: Dr. David Alan Gilbert
Subject: Re: [PATCH 0/5] Introduce 'yank' oob qmp command to recover from hanging qemu
Date: Wed, 13 May 2020 14:48:56 +0100
User-agent: Mutt/1.13.4 (2020-02-15)

* Daniel P. Berrangé (address@hidden) wrote:
> On Wed, May 13, 2020 at 01:56:24PM +0100, Dr. David Alan Gilbert wrote:
> > * Kevin Wolf (address@hidden) 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 / address@hidden / Manchester, UK




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