Subject: Re: When is export_operations.get_parent triggered?
To: "J. Bruce Fields" <bfields@fieldses.org>
References: <581DD7B0.8080906@osg.samsung.com>
 <8760o1pose.fsf@notabene.neil.brown.name> <581F20F4.2040304@osg.samsung.com>
 <20161107173415.GA13117@fieldses.org>
Cc: NeilBrown <neilb@suse.com>, linux-fsdevel@vger.kernel.org,
        Richard Weinberger <richard@nod.at>, linux-nfs@vger.kernel.org
From: Luis de Bethencourt <luisbg@osg.samsung.com>
Message-ID: <0752f0ca-e0fd-77fb-2a49-f54909c80243@osg.samsung.com>
Date: Tue, 8 Nov 2016 15:49:31 +0000
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In-Reply-To: <20161107173415.GA13117@fieldses.org>
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Sender: linux-nfs-owner@vger.kernel.org

On 07/11/16 17:34, J. Bruce Fields wrote:
> On Sun, Nov 06, 2016 at 12:24:20PM +0000, Luis de Bethencourt wrote:
>> On 05/11/16 22:03, NeilBrown wrote:
>>> On Sat, Nov 05 2016, Luis de Bethencourt wrote:
>>>
>>>> Hi all,
>>>>
>>>> I recently played with adding the basics to make befs exportable via NFS [0].
>>>>
>>>> I want to implement the get_parent member of the export_operations struct as
>>>> well, but I can't seem to trigger this member being called. I have implemented
>>>> a solution which I feel is wrong [1], but want to be able to test it before
>>>> moving forward.
>>>>
>>>> When is this member triggered? Any advice?
>>>
>>> This is required when a filehandle for a directory arrives, but the
>>> directory is not in the dcache.
>>> NFSD needs to find dentries for the directory, the parent, the
>>> grandparent etc all the way up to the root.
>>>
>>> The simplest way to trigger this is to mount the filesystem onto a
>>> different machine, 'cd' into a fairly deep directory, then reboot the
>>> server (or unexport, unmount, remount, re-export).
>>> Now 'ls -l' on the client.  That should trigger calls to ->get_parent.
>>>
>>> ->get_parent() is a log like performing a lookup of "..".
>>>
>>> NeilBrown
>>>
>>
>> Nice!
>>
>> This makes a lot of sense. I just rebooted the server and saw the get_parent
>> being called. Before I was mistakenly trying without a reboot, but thanks to your
>> explanation now understand this better, the directory was still in the dcache and
>> it was using this instead.
> 
> I've also tested get_parent with "echo 2>/proc/sys/vm/drop_caches",
> after first creating a 2000-deep subdirectory heirarchy (to stress
> performance, and to make sure dcache had enough entries that drop_caches
> would reliably drop what I wanted).  And I used the filehandle syscalls
> directly, to take nfsd out of the equation.  See deep-fh-lookup in
> git://linux-nfs.org/~bfields/fragments.git for my kludgey script.  OK,
> rebooting may be easier.
> 
> --b.
> 

Very interesting approach, stressing it.
Will add it to my repertoire.

Thanks,
Luis