Re: about NLM/NSM

[Peter Staubach <staubach@redhat.com>]

J. Bruce Fields wrote:
> On Mon, Oct 27, 2008 at 05:14:38PM -0400, Peter Staubach wrote:
>   
>> J. Bruce Fields wrote:
>>     
>>> On Mon, Oct 27, 2008 at 03:22:57PM -0400, Peter Staubach wrote:
>>>   
>>>       
>>>> J. Bruce Fields wrote:
>>>>     
>>>>         
>>>>> On Mon, Oct 27, 2008 at 02:49:27PM +0800, hexf wrote:
>>>>>         
>>>>>           
>>>>>> We are using nfsv3. Now we meet a demand. If a client which hold a
>>>>>> lock crash, after it reboot, its statd daemon can notify the nfs
>>>>>> server to release the lock.  But if this client will not reboot for
>>>>>> some reason(or will reboot after a long time), then the lock it
>>>>>> holding will not be released.In nfsv3 and nlmv4,it seems there is no
>>>>>> time-out mechnism for this situation. How would we solve this
>>>>>> question? My colleague advise me to modify the code of NLM/NSM to meet
>>>>>> this demand,but is seems quite a complicated work.Can you give me some
>>>>>> advice?
>>>>>>             
>>>>>>             
>>>>> It might be possible to modify the server so that it dropped all locks
>>>>> from a client it hadn't heard from in a while.  However, nfsv2/v3
>>>>> clients are not required to contact the server regularly while they hold
>>>>> locks.  So you may end up revoking locks held by perfectly good
>>>>> functioning clients.
>>>>>
>>>>> As an ugly workaround, rebooting the server will clear the problem, as
>>>>> it will notify clients to recover their locks on restart, and any dead
>>>>> clients will fail to recover their locks.
>>>>>
>>>>>         
>>>>>           
>>>> Didn't Wendy Cheng submit some patches to implement a
>>>> "clearlocks" sort of functionality?  What happened with
>>>> them?
>>>>     
>>>>         
>>> Yes, but that's motivated by the case of migrating all clients using one
>>> export; so it'll drop all locks held on a single filesystem, or all
>>> locks acquired using a single server (not client!) ip address.
>>>
>>> So if we want some finer-grained interface then that's yet to be
>>> designed.
>>>   
>>>       
>> Sorry, I guess that I was remembering incorrectly.  I was
>> thinking that she was looking for something like the clearlocks
>> functionality so that file systems could be migrated around
>> cleanly.
>>     
>
> That's what she was working on (and we merged), yes.
>
> But it doesn't help clear just the set of locks held by a single client.
>
>   
>> It seems for this situation, we could use this sort of variation.
>>     
>
> I'm losing track of what those two "this"'s refer to!
>   

Sorry -- :-)

For the situation of needing to clear locks belonging to long
dead and not returning clients, we could use a variation of
Wendy's proposal which works using the client IP as the key.

It is a rope with a very large and suspicious looking knot on
the end though...

       ps