Re: NFS locking bug -- limited mtime resolution means nfs_lock() does not provide coherency guarantee

From: Trond Myklebust (trond.myklebust@fys.uio.no)
Date: Tue Sep 12 2000 - 15:10:12 EST


>>>>> " " == Jeff Epler <jepler@inetnebr.com> writes:

> But "ctime and file size are the same" does not prove that the
            ^^^^^ mtime
> file is unchanged. That's the root of this problem, and why
> NFS_CACHEINV(inode) is not enough to ensure coherency.

Yes, but I just demonstrated that messing around with the client is a
hack, not a solution to this situation.
It's a hack because it is not compatible with the expected behaviour
of NFS clients. The NFSv4 draft demonstrates what the expected
behaviour is, and illustrates what we have to implement for a generic
fix (one that works on all clients -- not hacked Linux ones).

This is why I'm saying the correct solution is to get the server to
change mtime. To use the 'microseconds' field that is supported by the
NFS protocol, and that we currently set to 0.

Cheers,
  Trond
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