linux-kernel - Re: [DRIVER SUBMISSION] DRBD wants to go mainline

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Message-ID: <20070726091748.GA15925@2ka.mipt.ru>
Date:	Thu, 26 Jul 2007 13:17:48 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Kyle Moffett <mrlinuxman@....com>
Cc:	david@...g.hm, Satyam Sharma <satyam.sharma@...il.com>,
	Lars Ellenberg <lars.ellenberg@...bit.com>,
	Jens Axboe <axboe@...nel.dk>, Andrew Morton <akpm@...l.org>,
	LKML Kernel <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org
Subject: Re: [DRIVER SUBMISSION] DRBD wants to go mainline

Hi Kyle.

On Wed, Jul 25, 2007 at 11:43:38PM -0400, Kyle Moffett (mrlinuxman@....com) wrote:
> If you made all your sockets and inter-thread pipes nonblocking then  
> in userspace you would just epoll_wait() on the sockets and pipes and  
> be easily able to react to any IO from anywhere.
> 
> In kernel space there are similar nonblocking interfaces, although it  
> would probably be easier just to use a couple threads.

There are no such interfaces in kernel - one must create own state
machine on top of ->poll() callback, or use sys_poll()/epoll, but likely 
it is not what one wants for high-performance in-kernel event processing 
engine. Having two threads does not solve the problem - eventually one 
needs to send a header before receiving data. So, the solution would 
either to use always-blocking mode like in NBD, or create own state 
machine using ->poll() callbacks.

> Cheers,
> Kyle Moffett

-- 
	Evgeniy Polyakov
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