J. Bruce Fields :
> On Wed, May 19, 2010 at 05:46:23PM +0800, Mi Jinlong wrote:
>>
>> J. Bruce Fields :
>>> On Fri, May 14, 2010 at 02:31:12PM -0400, Trond Myklebust wrote:
>>>> On Fri, 2010-05-14 at 13:59 -0400, Trond Myklebust wrote:
>>>>> Note that the server should also recall the delegation if someone
>>>>> attempts to violate the guarantees that are listed in section 9.4: Open
>>>>> Delegation
>>>>>
>>>>> When a client has a read open delegation, it may not make any changes
>>>>> to the contents or attributes of the file but it is assured that no
>>>>> other client may do so. When a client has a write open delegation,
>>>>> it may modify the file data since no other client will be accessing
>>>>> the file's data. The client holding a write delegation may only
>>>>> affect file attributes which are intimately connected with the file
>>>>> data: size, time_modify, change.
>>>>>
>>>>> IOW: even if you hold a write delegation you are not allowed to change
>>>>> the file mode bits, owner, group or acls...
>>>> ...or the nlink value. So technically, we should also recall the
>>>> delegation when someone creates or deletes a hard link. I think I need
>>>> to remind Tom that he should add that to the RFC3530bis draft...
>>> Yep. And fixing all these cases is required before our the server's
>>> NFSv4 server is ready for much of anything.
>>>
>>> I'm not sure ading break_lease() to may_delete() is right, but maybe
>>> it's better than nothing.
>> Agree with you.
>>
>>> One problem is that there's a race: nothing I can see stops anyone from
>>> getting another lease after may_delete() but before the delete happens.
>> Yes.
>> The problem will exist, but there isn't some better methods to avoid it.
>> Is there a lease lock exist in kernel?
>> If that's true, the problem will be fixed simply.
>
> I don't know of any existing lock that does exactly what we want.
>
> Somebody at citi worked on a better lease implementation for a while,
> but I don't think we ever really got it right; the last version I can
> find is here:
>
> git://linux-nfs.org/~bfields/linux-topics.git leases
When reading the code of the git, i found a patch which try to fix
the lease's problem, but only for unlink.
commit id: d5a08e556116c66fb60a448f805a40bf54314634
msg: "leases: break file leases on unlink."
In this patch, it seems only add break_lease() and some other functions
but seems don't avoid the problem of race. Or there is some different
at break_lease() with the community's kernel.
Can you give me some message about the new lease? Thanks.
thanks,
Mi Jinlong
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