Re: open by handle support for NFS V2

From: DENIEL Philippe <philippe.deniel@cea.fr>
To: "Mkrtchyan, Tigran" <tigran.mkrtchyan@desy.de>,
	"J. Bruce Fields" <bfields@fieldses.org>
Cc: Trond Myklebust <trondmy@primarydata.com>,
	Christoph Hellwig <hch@lst.de>,
	Jeff Layton <jlayton@poochiereds.net>,
	linux-nfs <linux-nfs@vger.kernel.org>,
	schumaker anna <schumaker.anna@gmail.com>
Subject: Re: open by handle support for NFS V2
Date: Mon, 3 Jul 2017 08:39:32 +0200	[thread overview]
Message-ID: <d800776d-722a-0f20-5616-4d236e9d6130@cea.fr> (raw)
In-Reply-To: <995885135.19496849.1498901676399.JavaMail.zimbra@desy.de>

On 07/01/17 11:34, Mkrtchyan, Tigran wrote:
>
> ----- Original Message -----
>> From: "J. Bruce Fields" <bfields@fieldses.org>
>> To: "Trond Myklebust" <trondmy@primarydata.com>
>> Cc: "Christoph Hellwig" <hch@lst.de>, "Jeff Layton" <jlayton@poochiereds.net>, "linux-nfs" <linux-nfs@vger.kernel.org>,
>> "schumaker anna" <schumaker.anna@gmail.com>
>> Sent: Friday, June 30, 2017 7:38:18 PM
>> Subject: Re: open by handle support for NFS V2
>> On Fri, Jun 30, 2017 at 05:00:59PM +0000, Trond Myklebust wrote:
>>> The main use case for open by filehandle was (and still should be) the
>>> promise of being able to do the sort of tricks you normally associate
>>> with object storage on a standard filesystem.
>>>
>>> Imagine that you are trying to build an application for indexing and
>>> searching the data on your storage. You basically want to trawl through
>>> the filesystem on a regular basis and build up a database of key words
>>> and other metadata to tell you what is in the files. For that kind of
>>> application, the namespace is a real PITA to deal with, because files
>>> get renamed, moved and deleted all the time; so if you can store
>>> something that is independent of the namespace and that will give you
>>> access to the file contents, then why wouldn't you do so? Normally,
>>> applications like that use the inode number, but you can't open a file
>>> by inode number, and you have the same problems with inode number reuse
>>> that a NFS server has.
>>>
>>> That's the sort of thing I'd think we want to allow through open by
>>> filehandle, and I see no reason why NFS should be excluded from that
>>> type of application.
>> Thanks, that makes sense.
>>
>> We've had open_by_handle support for most filesystems since 2011, is
>> there evidence of anyone doing this?
>
> I am pretty sure that nfs-ganesha is using this in one the backend
> implementations.
>
> Tigran.
Tigran is right: nfs-ganesha does something a bit similar to this in its 
"FSAL_VFS" module (the backed module based the usage of on 
open_by_handle_at() and name_to_handle_at() ).

     regards

         Philippe

>
>> --b.
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