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SubjectRe: NFS Problem in Kernel 2.0.27: inode status not updated
Matthias Urlichs <smurf@work.smurf.noris.de> wrote:
> srb@cuci.nl (Stephen R. van den Berg) writes:
>> Tim Wright <timw@sequent.com> wrote:
>> >You cannot rely on ANY Unix filesystems semantics using NFSv2.

>> I agree that it's fairly bad. But, if you make sure that you're the
>> only client operating on a certain file which has never existed before,
>> the results aren't so bad (if the NFS-client and server are a good quality
>> implementation).

>Why should you want that?

In order to implement a locking scheme, or a maildir type mail delivery
system, that works across NFS.

>IMHO, relying on any such thing is evil. People will surely use your code
>in environments where that assumption doesn't hold; after all, it works (almost)
>flawlessly regardless, right?

>The "almost" is the problem.

It's not really a problem. The assumption is *not* a requirement to make
the code work correctly. If the assumption does not hold, two things
can happen:
- The code will work regardlessly, because it anticipates some kind of
deviation from the standard.
- The code will report a problem, and will refuse to continue.

>Read maildir(5), a manual page from the qmail system. It describes a reliable
>mail delivery system which works over NFS, even if multiple mail servers
>write to the same mail spool.

It makes use of the same assumptions I made to implement the
NFS-resistent-locking scheme. It wouldn't surprise me if Bernstein
took a good look at the locking scheme before creating the maildir
implementation.

>much yet, unfortunately. However, IMHO it's a much better idea to create a
>patch for elm which supports maildir than to invent yet another limited-use
>locking scheme.

This locking scheme predates the maildir implementation by more than six
years. So we're not inventing "yet another" locking scheme.
--
Sincerely, srb@cuci.nl
Stephen R. van den Berg (AKA BuGless).
"I don't like this word bomb. It is not a bomb, it is a device,
which explodes." French Ambassador about the atomic tests.

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