[libvirt] [PATCH 0/4] Move ccwaddrs and pciaddrs to domainDef

[Laine Stump]

On 06/20/2016 10:26 PM, Tomasz Flendrich wrote:
>> Apologies if I'm missing something, I didn't look too closely at this series,
>> however have you seen this thread?
>>
>> http://www.redhat.com/archives/libvir-list/2016-May/msg01071.html
> I haven’t noticed that some work has been done on that, thank you!
>
>> My understanding of the current code is that the cached vioserial/ccw/pciaddrs
>> lists in qemu aren't actually required…they were at one point to handle
>> older qemu, but we dropped that support. Maybe you can pick up my patches and
>> finish off dropping of pciaddrs and ccwaddrs? I suspect the pciaddrs cache in
>> bhyve can be dropped as well, I don't think it was ever strictly required, the
>> code just followed the qemu example
> If we could do without the caching, it would make the current code simpler.
> There wouldn’t be those booleans in qemu_hotplug.c that remember whether
> an address has to be deleted or not in case something fails. We could
> delete qemuDomainReleaseDeviceAddress() and a few more functions.

I'm completely ignorant about vioserial and ccw. As far as the "cache" 
for pci addresses, I guess whether or not we want the cache depends 
completely on how long it takes to reconstruct vs. how often a device is 
added. There is also the issue of the mismatch between live and config 
devices' address use, and the inconsistency that can be caused by that 
(if you hotplug a device with --live, then hotplug another with --live 
--config, then the 2nd device will have the same address in config as 
the first has in the live state of the guest (more importantly, the 
address of the 2nd device will change the next time the domain is 
shutdown and restarted, which all of this address assignment stuff is 
intended to avoid) - I don't know if that problem would be more easily 
solved by a cache that is used for assigning addresses for both --live 
and --config, or if, as Cole suggests, it would be better just to remove 
the cache and rebuild the allocation table each time a new device is 
added (this would mean that we would need to scan through all the live 
devices *and* persistent devices to re-populate it)

>
> I examined vioserial and pci addresses and it looks like
> it could be done. However, I'm not an expert on qemu_hotplug yet
> and this is where the interesting stuff happens with addresses,
> so I am not entirely sure yet.
> I also don't know what the plans are for device addresses in the future.
> Perhaps there are some features that will require caching them.
>
> I think that recalculation may change the current behavior of ccw addresses.
> Function virDomainCCWAddressReleaseAddr() modifies addrs->next
> only when the address being released was the address most recently
> assigned.
>
> Laine, you know a lot about PCI addresses and you also mentioned that
> you want to modify them in the future. What do you think?


"in the future" sounds so distant :-). Within the next week I will be 
modifiying the PCI address allocation to eliminate the auto-adding of 
pci-bridge devices whenever there aren't enough free slots, and  instead 
add a new controller of the appropriate type for each extra slot that is 
needed. I haven't been able to concentrate enough to determine if that 
is going to cause any merge conflict with what you're going to do.


>
> Martin, should I work on that instead?
>
>
> Kind regards,
> Tomasz