[libvirt] [PATCH 0/4] qemu_hotplug: Check for duplicate drive addresses

[Jim Fehlig]

On 4/12/19 3:16 AM, Michal Privoznik wrote:
> On 4/11/19 8:36 PM, Daniel Henrique Barboza wrote:
>>
>>
>> On 4/11/19 11:34 AM, Michal Privoznik wrote:
>>> This is an alternative approach to:
>>>
>>> https://www.redhat.com/archives/libvir-list/2019-March/msg01111.html
>>>
>>> which caused regression to which a proposed fix is here:
>>>
>>> https://www.redhat.com/archives/libvir-list/2019-April/msg00756.html
>>>
>>> One of the selling points was that having this check in
>>> virDomainDefCompatibleDevice() will fix the problem across all drivers.
>>> Well, turns out, some drivers don't care (e.g. lxc) and some have a
>>> different workflow and thus don't need that check.
>>
>> Just tested the patch series and it fixes the problem for SCSI disks, as
>> expected.
>>
>> The major drawback of reverting that patch is that we lose the address
>> check not just for other drivers (that might not care much for that), but
>> also for the remaining device types other than SCSI disks.
>>
>> Now, taking a quick look in the code I see that there are similar checks
>> being made in VDA, PCI and DIMM type devices (didn't check the remaining
>> devices). If there are address redundancy checks for all other devices, then
>> the patch can be reverted without loss.
> 
> Yep, other types of addresees are covered. At least in drivers that do care. LXC 
> doesn't because it doesn't make much sense there. I mean, a container shares HW 
> with the host, so we can't really make it appear at different addresses. For 
> instance, when plugging a disk into an LXC container it'll appear at the same 
> adddess as in the host and no <address/> in the XML is going to change that.
> 
> That's why I vouche for this approach. Sorry for not realizing this the first time.

I agree with this approach as well. IMO the check should be done in the 
hypervisor drivers, where there is more knowledge about what is permissible wrt 
the various device types.

Regards,
Jim

> 
>>
>> It is worth mentioning that the first 2 patches can be applied regardless of
>> what it is decided to do about the address checking, since they are a straight
>> improvement in what already exists.
> 
> Thanks,
> 
> Michal
> 
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