linux-kernel - RE: Finding hardlinks

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Message-ID: <E472128B1EB43941B4E7FB268020C89B149CEC@riverside.int.panasas.com>
Date:	Thu, 28 Dec 2006 15:07:43 -0500
From:	"Halevy, Benny" <bhalevy@...asas.com>
To:	"Mikulas Patocka" <mikulas@...ax.karlin.mff.cuni.cz>
Cc:	"Jeff Layton" <jlayton@...chiereds.net>,
	"Arjan van de Ven" <arjan@...radead.org>,
	"Jan Harkes" <jaharkes@...cmu.edu>,
	"Miklos Szeredi" <miklos@...redi.hu>,
	<linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<nfsv4@...f.org>
Subject: RE: Finding hardlinks

Mikulas Patocka wrote:
> 
>>> This sounds like a bug to me. It seems like we should have a one to one
>>> correspondence of filehandle -> inode. In what situations would this not be the
>>> case?
>>
>> Well, the NFS protocol allows that [see rfc1813, p. 21: "If two file handles from
>> the same server are equal, they must refer to the same file, but if they are not
>> equal, no conclusions can be drawn."]
>>
>> As an example, some file systems encode hint information into the filehandle
>> and the hints may change over time, another example is encoding parent
>> information into the filehandle and then handles representing hard links
>> to the same file from different directories will differ.
>
>BTW. how does (or how should?) NFS client deal with cache coherency if 
>filehandles for the same file differ?
>

Trond can probably answer this better than me...
As I read it, currently the nfs client matches both the fileid and the
filehandle (in nfs_find_actor). This means that different filehandles
for the same file would result in different inodes :(.
Strictly following the nfs protocol, comparing only the fileid should
be enough IF fileids are indeed unique within the filesystem.
Comparing the filehandle works as a workaround when the exported filesystem
(or the nfs server) violates that.  From a user stand point I think that
this should be configurable, probably per mount point.

>Mikulas
>
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