Re: about NLM/NSM

["J. Bruce Fields" <bfields@fieldses.org>]

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.

--b.