[libvirt PATCH v3 00/21] Add support for persistent mediated devices

[Daniel P. Berrangé]

On Thu, Jan 07, 2021 at 05:50:10PM +0100, Erik Skultety wrote:
> On Thu, Dec 24, 2020 at 08:14:24AM -0600, Jonathon Jongsma wrote:
> > This patch series follows the previously-merged series which added support for
> > transient mediated devices. This series expands mdev support to include
> > persistent device definitions. Again, it relies on mdevctl as the backend.
> > 
> > It follows the common libvirt pattern of APIs by adding the following new APIs
> > for node devices:
> >     - virNodeDeviceDefineXML() - defines a persistent device
> >     - virNodeDeviceUndefine() - undefines a persistent device
> >     - virNodeDeviceCreate() - starts a previously-defined device
> > 
> > It also adds virsh commands mapping to these new APIs: nodedev-define,
> > nodedev-undefine, and nodedev-start.
> > 
> > Since we rely on mdevctl for the definition of ediated devices, we need a way
> > to stay up-to-date with devices that are defined by mdevctl (outside of
> > libvirt).  The method for staying up-to-date is currently a little bit crude
> > due to the fact that mdevctl does not emit any events when new devices are
> > added or removed. As a workaround, we create a file monitor for the mdevctl
> > config directory and re-query mdevctl when we detect changes within that
> > directory. In the future, mdevctl may introduce a more elegant solution.
> > 
> > changes in v3:
> >  - streamlined tests -- removed some unnecessary duplication
> >  - split out patch to factor out node device name generation function
> >  - split nodeDeviceParseMdevctlChildDevice() into a separate function
> >  - added follow-up patch to remove space-padded alignment in header
> >  - refactored the mdevctl update handling significantly:
> >    - no longer a separate persistent thread that gets signaled by a timer
> >    - now piggybacks onto the existing udev thread and signals the thread in t=
> > he
> >      same way that the udev event does.
> >    - Daniel suggested spawning a throw-away thread to handle mdevctl updates,
> >      but that introduces the complexity of possibly serializing multiple
> >      throw-away threads (e.g. if we get an 'created' event followed immediate=
> > ly
> >      by a 'deleted' event, two threads may be spawned and we'd need to ensure
> >      they are properly ordered)
> >  - added virNodeDeviceObjListForEach() and virNodeDeviceObjListRemoveLocked()
> >    to simplify removing devices that are removed from mdevctl.
> >  - coding style fixes
> >  - NOTE: per Erik's request, I experimented with changing the way that mdevctl
> >    commands were generated and tested (e.g. introducing something like
> >    virMdevctlGetCommand(def, MDEVCTL_COMMAND_<SUBCOMMAND>, ...)), but it was
> >    too invasive and awkward and didn't seem worthwhile
> 
> Thanks for giving ^this a try :)
> 
> I think we're converging nicely with the only remaining bit to agree on being
> the mdevctl monitoring thread. I think we can target 7.1.0 with this series.

The lifecycle events handling in this series is totally broken and needs
addressing before we can consider merging.


Regards,
Daniel
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