Re: [PATCH] tests/qemu_iotests: Minimize usage of used ports

[Max Reitz <mreitz@redhat.com>]

On 06.02.20 19:33, Lukáš Doktor wrote:
> Dne 06. 02. 20 v 17:59 Max Reitz napsal(a):
>> On 06.02.20 17:48, Eric Blake wrote:
>>> On 2/6/20 10:37 AM, Max Reitz wrote:

[...]

>>>> OTOH, would it work if we just did a %s/localhost/127.0.0.1/ in the
>>>> test?  We have specific cases for IPv6, so I think it makes sense to
>>>> force IPv4 in all other cases.
>>>
>>> Except then it will fail on machines configured for IPv6-only.
>>
>> So we’ll just have to test whether IPv4 works, just like we already do
>> for IPv6, no?
>>
> 
> Sure, using ::1 for IPv6 and 127.0.0.1 for IPv4 cases would work. The question is whether the behavior is really expected. In migration it was considered dangerous, because you can have 2 VMs starting the migration at the same time. They both might attempt to get the same port, one would receive IPv4 the other IPv6. Then depending on the order of start migrate you might end-up attempting to migrate the other VMs instead of the intended ones.
> 
> The same can happen here, you might start 2 nbd exports at the same time, get the same port without any failures and then depending on luck get the right or wrong export when attempting to connect. So I think bailing out in case we fail to get all interfaces would be the most appropriate (note the same situation is for 0.0.0.0 where you might end-up serving multiple different disks on different interfaces). Anyway I leave it to you. If you decide you don't want to fail than using ::1/127.0.0.1 sounds like a good idea. Otherwise it'd make sense to create a test that especially uses ::1 and then localhost to make sure it bails-out.

OK.  I’ll defer to Eric on that one. O:-)

Max