netdev - Re: [RFC Patch] net: reserve ports for applications using fixed portnumbers

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Message-Id: <201002051808.BFJ51557.SLQFtJVMOOFFOH@I-love.SAKURA.ne.jp>
Date:	Fri, 5 Feb 2010 18:08:15 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	bvanassche@....org
Cc:	amwang@...hat.com, linux-kernel@...r.kernel.org,
	eric.dumazet@...il.com, linux-rdma@...r.kernel.org,
	netdev@...r.kernel.org, nhorman@...driver.com,
	linux-sctp@...r.kernel.org, davem@...emloft.net
Subject: Re: [RFC Patch] net: reserve ports for applications using fixed portnumbers

Cong Wang wrote:
> The problem is that there are some existing applications which use
> fixed port number, we don't have chances to change this for them,
> thus making them working is desired, so they want to reserve these
> port for those applications.
> 
> For example, if I have an appliction which uses port 40000, but
> before this application starts, another application gets this port
> number by bind() with port 0 (i.e. chosen by kernel), in this case,
> that application will fail to start. Again, we don't have any chance
> to change the source code of that application.
> 
And there is a utility called "portreserved" (port reserve daemon).
http://fedoraproject.org/wiki/Features/Portreserve

But that utility cannot close the race window between "portreserved stops
reserving local port numbers" and "applications starts using local port
numbers which portreserved was reserving".

Thus, I think people want to have port reservation mechanism inside kernel
(if it has little impact).
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