netdev - RE: [PATCH] net: Fragment large datagrams even when IP

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Message-ID: <BN3PR0201MB10599C7780CBC6EB4BC2894DF9550@BN3PR0201MB1059.namprd02.prod.outlook.com>
Date:	Wed, 15 Jun 2016 10:41:56 +0000
From:	Alan Davey <Alan.Davey@...aswitch.com>
To:	David Miller <davem@...emloft.net>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"kuznet@....inr.ac.ru" <kuznet@....inr.ac.ru>,
	"jmorris@...ei.org" <jmorris@...ei.org>,
	"yoshfuji@...ux-ipv6.org" <yoshfuji@...ux-ipv6.org>,
	"kaber@...sh.net" <kaber@...sh.net>
Subject: RE: [PATCH] net: Fragment large datagrams even when IP_HDRINCL is
 set.

From: David Miller [mailto:davem@...emloft.net] 
Sent: 08 June 2016 18:26

>> -  The current behaviour is counter-intuitive (fragmentation takes
>> -  place in all other cases) and therefore different to what
>> -  everyone expects.
>
> But it's what all existing applications must expect, and as you have seen in these replied they absolutely do.
>
> You cannot just break things on people like this.

The only case that would break is that where an application relies on the existing (documented as a bug) feature of getting an EMSGSIZE return code in the case of an over-sized packet.  Applications that perform their own fragmentation would be unaffected.

I think that the benefit of the patch, in moving all fragmentation and reassembly into the kernel, outweigh the very small chance that applications rely on the send of an over-sized packet failing.

What is your thinking on taking the patch?

Regards
Alan