SCTP MSG_MORE code

SCTP MSG_MORE code

[David Laight]

Something needs to be done with SCTP MSG_MORE before the end of the rc cycle.
The current code is definitely broken.

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.

	David

Re: SCTP MSG_MORE code

[Xin Long]

On Tue, Mar 21, 2017 at 1:49 AM, David Laight <David.Laight@aculab.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'.

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.

>         David
>
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RE: SCTP MSG_MORE code

[David Laight]

From: Xin Long
> Sent: 21 March 2017 06:01
> On Tue, Mar 21, 2017 at 1:49 AM, David Laight <David.Laight@aculab.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