[libvirt] [PATCHv3 1/2] network: added waiting for DAD to finish for bridge address.

[Laine Stump]

On 10/19/2015 08:36 AM, Maxim Perevedentsev wrote:
>
>
> On 10/16/2015 08:13 PM, Laine Stump wrote:
>> On 10/16/2015 12:51 PM, Maxim Perevedentsev wrote:
>>> On 10/15/2015 09:03 PM, Laine Stump wrote:
>>>> This loop *really* bothers me, because there is no failsafe to 
>>>> terminate it if we never get positive notification that DAD has 
>>>> completed. This would lock up the network driver startup, which 
>>>> would lock up libvirtd startup. I think we need to decide on what 
>>>> is the maximum time this could possibly take to complete (maybe it 
>>>> is somehow based on the number of interfaces? or maybe it doesn't 
>>>> matter...) and timeout from the loop after the appropriate iterations.
>>> I did not hear about general timeout for this operation. Maybe 5 
>>> min, for example?
>>
>> 5 minutes is a very long time when everything else is being held up. 
>> If the wait for each network is much beyond a couple seconds, we'll 
>> need to think about spawning off a thread to wait for DAD.
>>
>> (if you're curious where the single-threadedness is, look at 
>> virStateInitialize() - it calls the stateAutoStart() function for 
>> each subsystem driver in sequence, and within the stateAutoStart() 
>> for the network driver, each network with autostart set is called in 
>> sequence).
> I looked at kernel sources. It looks like DAD time is configurable:
> rand() % net.ipv6.conf.default.router_solicitation_delay [1s] + 
> net.ipv6.conf.default.dad_transmits [1] * 
> net.ipv6.neigh.default.retrans_time_ms [1000ms]
>
> By default on my machine, it gives 0s + 1 * 1000ms = 1s maximum.
> Kernel keeps track of DAD success (on timeout) / fail. We could take 
> these variables from sysctl, but this is cumbersome. I suggest taking 
> 5s as maximum timeout and hope this is not too long.
>
> Yes, I *really* do not want to write this thread-related stuff :)

I agree. I think it would be okay to put a 5s timeout on the loop. We 
should probably have a VIR_DEBUG before we start waiting for DAD, and 
another when we're finished, so that someone experiencing long delays in 
startup will be able to determine the reason.