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Date: Thu, 20 Feb 2014 18:29:32 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: "Zuckerman, Boris" <borisz@hp.com>
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>,
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        Linux-Fsdevel <linux-fsdevel@vger.kernel.org>,
        "J. Bruce Fields" <bfields@citi.umich.edu>,
        Yongzhi Pan <panyongzhi@gmail.com>
Subject: Re: Update of file offset on write() etc. is non-atomic with I/O
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On Thu, Feb 20, 2014 at 06:15:15PM +0000, Zuckerman, Boris wrote:
> Hi,
> 
> You probably already considered that - sorry, if so…
> 
> Instead of the mutex Windows use ExecutiveResource with shared and exclusive semantics. Readers serialize by taking the resource shared and writers take it exclusive. I have that implemented for Linux. Please, let 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?