linux-kernel - Re: Update of file offset on write() etc. is non-atomic with I/O

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Date:	Thu, 20 Feb 2014 18:29:32 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	"Zuckerman, Boris" <borisz@...com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	Theodore T'so <tytso@....edu>, Christoph Hellwig <hch@....de>,
	Chris Mason <clm@...com>, Dave Chinner <david@...morbit.com>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	"J. Bruce Fields" <bfields@...i.umich.edu>,
	Yongzhi Pan <panyongzhi@...il.com>
Subject: Re: Update of file offset on write() etc. is non-atomic with I/O

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?
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