Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!amdcad!ames!ll-xn!mit-eddie!husc6!cmcl2!brl-adm!brl-smoke!gwyn
From: gwyn@brl-smoke.ARPA (Doug Gwyn )
Newsgroups: comp.lang.c
Subject: Re: BSD ?= SysV File Locking
Message-ID: <6594@brl-smoke.ARPA>
Date: Mon, 26-Oct-87 16:21:07 EST
Article-I.D.: brl-smok.6594
Posted: Mon Oct 26 16:21:07 1987
Date-Received: Wed, 28-Oct-87 22:24:32 EST
References: <463@petro.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Distribution: na
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 24
Keywords: lockf

In article <463@petro.UUCP> jrb@petro.UUCP (Jon Boede) writes:
>Does BSD use the lockf() convention like SysV?  I've localized functions using
>it in hopes that if it didn't I'd only have to fiddle with one area.  If it
>doesn't, what does the file locking under BSD 4.3 look like?

flock() was adopted from the 1984 /usr/group Standard and earlier
drafts of IEEE 1003.1.  Later drafts of IEEE 1003.1 (POSIX) have
adopted the more general locking provided by fcntl() on SVR2+ and
later.  Berkeley systems have for some time supplied flock(),
which is not identical to either of the other two.  The lockf()
and flock() approaches can be emulated using fcntl() locking.

It is good that you've localized this function, so that you can
easily adapt it to other file locking kernel interfaces.

The 4.2BSD version:
	#include <sys/file.h>
	/* defines the following advisory lock symbols used to construct
	   an "operation" code for flock(): */
	/* #define LOCK_SH	1	/* shared (read) lock */
	/* #define LOCK_EX	2	/* exclusive (write) lock */
	/* #define LOCK_NB	4	/* don't block when locking */
	/* #define LOCK_UN	8	/* unlock */
	extern int flock(int fd, int operation); /* returns 0 if successful */