RE: Finding hardlinks

From: Halevy, Benny
Date: Thu Dec 28 2006 - 15:09:01 EST

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.

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