From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: Update of file offset on write() etc. is non-atomic with I/O
Date: Thu, 20 Feb 2014 18:29:32 +0000
Message-ID: <20140220182932.GF18016@ZenIV.linux.org.uk>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
	lkml <linux-kernel@vger.kernel.org>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Theodore T'so <tytso@mit.edu>, Christoph Hellwig <hch@lst.de>,
	Chris Mason <clm@fb.com>, Dave Chinner <david@fromorbit.com>,
	Linux-Fsdevel <linux-fsdevel@vger.kernel.org>,
	"J. Bruce Fields" <bfields@citi.umich.edu>,
	Yongzhi Pan <panyongzhi@gmail.com>
To: "Zuckerman, Boris" <borisz@hp.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
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On Thu, Feb 20, 2014 at 06:15:15PM +0000, Zuckerman, Boris wrote:
> Hi,
>=20
> You probably already considered that - sorry, if so=E2=80=A6
>=20
> Instead of the mutex Windows use ExecutiveResource with shared and ex=
clusive semantics. Readers serialize by taking the resource shared and =
writers take it exclusive. I have that implemented for Linux. Please, l=
et me know if there is any interest!

See include/linux/rwsem.h...

Anyway, the really interesting question here is what does POSIX promise
wrt lseek() vs. write().  What warranties are given there?