netdev - RE: SCTP MSG

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Date:   Thu, 23 Mar 2017 16:11:12 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Xin Long' <lucien.xin@...il.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Neil Horman <nhorman@...driver.com>
CC:     "linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: SCTP MSG_MORE code

From: Xin Long
> Sent: 21 March 2017 06:01
> On Tue, Mar 21, 2017 at 1:49 AM, David Laight <David.Laight@...lab.com> wrote:
> > Something needs to be done with SCTP MSG_MORE before the end of the rc cycle.
> > The current code is definitely broken.
> agreed.
> 
> >
> > I objected to the last 'fix' patch because it clears the flag is a place where
> > I don't think it is necessary to do so - so could generate extra ethernet frames.
> >
> Sorry, can you double check the last 'fix' patch ?
> I could not get 'generate extra ethernet frames'.

It would require the connection be 'flow controlled' and/or have
retransmissions.
Otherwise 'data chunk only' ethernet frames are only generated in response
to send() so would always see the value from the last send().

> if we keep sending data with "MSG_MORE", after one ethernet frame
> is sent, "followed by a second ethernet frame with 1 chunk in it" will NOT
> happen, as in this loop the asoc's msg_more flag is still set, and this flush
> is called by sctp_sendmsg(the function msg_more should care more).
> 
> 
> If your point about "generate extra ethernet frames"  is right, sure, I will
> change the way to fix that. but before this, pls check it again, appreciate it.

I won't be able to test this in the short term.

	David