linux-kernel - Re: [PATCH 2/2] NBD: allow hung network I/O to be cancelled

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Date:	Fri, 24 Aug 2007 15:09:17 -0400
From:	Paul Clements <paul.clements@...eleye.com>
To:	Mike Snitzer <snitzer@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, david@...eaves.com,
	Wouter Verhelst <w@...r.be>,
	Corey Minyard <cminyard@...sta.com>,
	nbd-general@...ts.sourceforge.net
Subject: Re: [PATCH 2/2] NBD: allow hung network I/O to be cancelled

Mike Snitzer wrote:
> On 8/24/07, Paul Clements <paul.clements@...eleye.com> wrote:
>> This patch allows NBD I/O to be cancelled when a network outage occurs.
>> Previously, I/O would just hang, and if enough I/O was hung in nbd, the
>> system (at least user-level) would completely hang until a TCP timeout
>> (default, 15 minutes) occurred.
>>
>> The patch introduces a new ioctl NBD_SET_TIMEOUT that allows a transmit
>> timeout value (in seconds) to be specified. Any network send that
>> exceeds the timeout will be cancelled and the nbd connection will be
>> shut down. I've tested with various timeout values and 6 seconds seems
>> to be a good choice for the timeout. If the NBD_SET_TIMEOUT ioctl is not
>> called, you get the old (I/O hang) behavior.
> 
> Hi Paul,
> 
> Thanks for implementing this!  Do you happen to have an associated
> nbd-client patch for userspace?  If not I'd be happy to coordinate
> with you and Wouter on a patch.

No, I don't. I just basically hardcoded my nbd-client to do a 6 second 
timeout by default, but Wouter will probably want to do something a 
little less hackish for the official nbd-client.

--
Paul
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