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NFS file locking (was: Re: Automake's file locking (was Re: Autoconf/Aut

From: Perry Hutchison
Subject: NFS file locking (was: Re: Automake's file locking (was Re: Autoconf/Automake is not using version from AC_INIT))
Date: Thu, 28 Jan 2021 18:27:47 -0800
User-agent: nail 11.25 7/29/05

Zack Weinberg <!zackw> wrote:
> ...
> grumpy aside in OpenBSD's "fcntl(2)" manpage:
> | This interface follows the completely stupid semantics of System V
> | and IEEE Std 1003.1-1988 ("POSIX.1") that require ...
> As I recall, at the time, *neither* flock nor fcntl locks
> were honored *at all* over NFS, so that wouldn't have been
> a consideration.

FWIW, NFS attempted to support some form of file locking at least as
far back as SunOS 3.5, which IIRC predated both SysV and POSIX.  Old-
timers may remember occasional patches to "statd" and "lockd".

I say "attempted" because _correct_ support of network file locking is
fundamentally incomputable in the presence of (transient, recoverable)
communication failures and (non-recoverable) system crashes:  the fact
that the server has not heard from the client (or vice versa) within
some period of time might mean either that the other party has crashed
(and may -- or may not ever -- come back), or that network connectivity
has been lost (and will, presumably, be restored at some unknown future

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