Re: Urgent help needed on an NFS question, please help!!!

From: Matthew Wilcox
Date: Thu Aug 10 2006 - 12:52:25 EST

On Thu, Aug 10, 2006 at 12:23:12PM -0400, Xin Zhao wrote:
> That makes sense.
> Can we make the following two conclusions?
> 1. In a single machine, inode+dev ID+i_generation can uniquely identify a
> file


> 2. Given a stored file handle and an inode object received from the
> server, an NFS client can safely determine whether this inode
> corresponds to the file handle by checking the inode+dev+i_generation.

The NFS client makes up its own inode numbers for use on the local
machine. It doesn't know the device+inode+generation numbers on the
server (and indeed, the server may not even have the concepts of
inodes). To quote RFC 1813:

The file handle contains all the information the server needs to
distinguish an individual file. To the client, the file handle is
opaque. The client stores file handles for use in a later request
and can compare two file handles from the same server for equality by
doing a byte-by-byte comparison, but cannot otherwise interpret the
contents of file handles. 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. Servers should try to maintain
a one-to-one correspondence between file handles and files, but this
is not required. Clients should use file handle comparisons only to
improve performance, not for correct behavior.
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