When is export_operations.get_parent triggered?

When is export_operations.get_parent triggered?

[Luis de Bethencourt]

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?

Thanks,
Luis


[0] https://lkml.org/lkml/2016/11/5/40
[1] https://github.com/luisbg/linux-befs/commit/a7d92c746469f1bd60dd1c905587915ecf9884f5

Re: When is export_operations.get_parent triggered?

[NeilBrown]

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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

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Re: When is export_operations.get_parent triggered?

[Luis de Bethencourt]

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.

Thank you Neil,
Luis

Re: When is export_operations.get_parent triggered?

[J. Bruce Fields]

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.

Re: When is export_operations.get_parent triggered?

[Luis de Bethencourt]

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