netdev - Re: inet_hash_connect: source port allocation

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Message-ID: <4CF3F114.2070108@oracle.com>
Date:	Mon, 29 Nov 2010 18:29:40 +0000
From:	John Haxby <john.haxby@...cle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	NetDev <netdev@...r.kernel.org>
Subject: Re: inet_hash_connect: source port allocation

On 29/11/10 17:26, Eric Dumazet wrote:
> Le lundi 29 novembre 2010 à 17:04 +0000, John Haxby a écrit :
>> Hello,
>>
>> Please forgive me if this is a stupid question, but is there any
>> particular reason why the source port allocation in
>> __inet_hash_connect() shouldn't use the same random allocation that
>> inet_csk_get_port() uses?  The latter, of course, is used when bind()
>> doesn't specify a source port but the implicit "bind" for a connect()
>> gets its port allocated by __inet_hash_connect().
>>
>> jch
> autobind vs bind
>
> bind() gives more information, like local address (if any)
>
> autobind(), we dont know local address, it'll be chose later by routing.

Sorry,  I think I phrased my question badly.

inet_csk_get_port() starts its search for a free port with

     smallest_rover = rover = net_random() % remaining + low;

whereas __inet_hash_connect() basically misses out that call to 
net_random() so you get a predictable port number.

Is there any good reason why that is the case?

jch


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