[libvirt] [PATCH] util: set error if DAD is not finished

[lhuang]

On 10/30/2015 02:15 AM, Laine Stump wrote:
> On 10/29/2015 08:32 AM, Maxim Perevedentsev wrote:
>> On 10/29/2015 12:47 PM, Luyao Huang wrote:
>>> If DAD not finished in 5 seconds, user will get an
>>> unknown error like this:
>>>
>>>   # virsh net-start ipv6
>>>   error: Failed to start network ipv6
>>>   error: An error occurred, but the cause is unknown
>>>
>>> Call virReportError to set an error.
>>>
>>> Signed-off-by: Luyao Huang <lhuang at redhat.com>
>>> ---
>>> I found the DAD will take 7 seconds
>>> on my machine, and i cannot create a network which
>>> use ipv6 now :( . Can we offer a way allow user to change this
>>> timeout ? maybe add a configuration file option in
>>> libvirtd.conf.
>>
>> Could you please send the related records of your sysctl -a?
>> Max DAD timeout should be
>> rand() % net.ipv6.conf.default.router_solicitation_delay + 
>> net.ipv6.conf.default.dad_transmits * 
>> net.ipv6.neigh.default.retrans_time_ms
>> I wonder whether my calculations were faulty or it is your specific 
>> configuration.
>>
>
> On my system, these are set to 1, 1, and 1000, and I've found that DAD 
> takes something between 5.7 and 6.8 seconds to complete (it was at the 
> lower end with a single IP address, and at the high end with 70 IP 
> addresses (or also with 20 IPs, so I don't think it's going to get 
> substantially higher). (Too bad I didn't do this *before* I pushed, 
> rather than relying on a successful build and reports of proper 
> operation on your system :-/)
>
> Based on that, I think it makes sense to push a patch that sets the 
> timeout to 20 seconds (and push Luyao's patch ragardless). Since the 
> timeout is meant to catch an "infinite" wait, I think 20 seconds is 
> okay; I don't want to add yet another tunable parameter unless we 
> really need to.
>

yes, change the timeout to 20 seconds is a good way to avoid this issue. 
I was trying to figure out why DAD take so long time on my machine.

And thanks a lot for your quick review.

Luyao