[dm-devel] [PATCH 28/57] libmultipath: use a shared lock to co-operate with udev

[Germano Percossi]

Hi,

Sorry for jumping in the middle of patch review

On 05/03/2016 03:27 PM, Benjamin Marzinski wrote:
> On Tue, May 03, 2016 at 07:57:01AM +0200, Hannes Reinecke wrote:
>> On 05/02/2016 06:26 PM, Benjamin Marzinski wrote:
>>> On Wed, Apr 27, 2016 at 01:10:29PM +0200, Hannes Reinecke wrote:
>> This is primarily for co-operation with udev.
>> As we typically do _not_ use multipath for creating device-mapper tables
>> the synchronisation problem between multipath and multipathd
>> doesn't typically occur.
>> At least not for us :-)
>
> Well, it doesn't occur for us either, unless someone runs multipath at
> EXACTLY the wrong time, at which case, I'm pretty sure the same thing
> can happen in any distro. The question is, do we protect against that
> very unlikely occurance.  The only time I see this actually having any
> real chance to occur would be if some multipath user writes a script
> that listens for new devices to be discovered, and then *helpfully* runs
> multipath to update the system. I have seen this. Multiple times, in
> fact. I'm not sure how much work we need to expend saving these people
> from themselves, however.
>

I just want to make sure XenServer is not among those that need to
be saved from themselves.
We do mix multipathd and multipath commands but in a way that we think
is safe: we add devices with "multipath -r" and remove with "multipath -f".
This is because we slightly bend the wwids file usage to be used
as a blacklisting mechanism (in our own way).

I am wondering if removing cooperation between multipath and multipathd
is going to cause us troubles in the future.

Regards,
Germano