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Re: [libvirt] [PATCH v2 6/7] domain_lock: Implement metadata locking



On Mon, Aug 20, 2018 at 04:07:28PM +0100, Daniel P. Berrangé wrote:
> On Tue, Aug 14, 2018 at 01:19:42PM +0200, Michal Privoznik wrote:
> > In order for our drivers to lock resources for metadata change we
> > need set of new APIs. Fortunately, we don't have to care about
> > every possible device a domain can have. We care only about those
> > which can live on a network filesystem and hence can be accessed
> > by multiple daemons at the same time. These devices are covered
> > in virDomainLockMetadataLock() and only a small fraction of
> > those can be hotplugged (covered in the rest of the introduced
> > APIs).
> 
> I'm not sure I understand the rationale behind saying we only care
> about resources on network filesystems.
> 
> If I have 2 locally running guests, and both have a serial port
> backed by a physical serial port, eg
> 
>   <serial type="dev">
>     <source path="/dev/ttyS0"/>
>     <target port="1"/>
>   </serial>
> 
> we *do* care about locking /dev/ttyS0, as libvirtd isn't doing
> mutual exclusion checks anywhere else for the /dev/ttyS0 device
> node.
> 
> In general I think we need to lock every single file resource
> that is labelled for a guest, regardless of whether its local
> or remote.

In the next patch I propose integration into the security manager that
would avoid the need to touch this domain lock abstraction at all.

Regards,
Daniel
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