On Fri, Jan 29, 2016 at 11:57:46AM +0100, Michael Tuexen wrote: > > On 29 Jan 2016, at 02:18, Marcelo Ricardo Leitner > > <marcelo.leit...@gmail.com> wrote: > > > > On Fri, Jan 29, 2016 at 12:36:05AM +0100, Michael Tuexen wrote: > >> > >>> On 28 Jan 2016, at 22:03, Marcelo Ricardo Leitner > >>> <marcelo.leit...@gmail.com> wrote: > >>> > >>> On Thu, Jan 28, 2016 at 06:54:06PM +0100, Michael Tuexen wrote: > >>>>> On 28 Jan 2016, at 14:51, David Laight <david.lai...@aculab.com> wrote: > >>>>> > >>>>> From: Marcelo Ricardo Leitner > >>>>>> Sent: 27 January 2016 17:07 > >>>>>> This patchset is merely a RFC for the moment. There are some > >>>>>> controversial points that I'd like to discuss before actually proposing > >>>>>> the patches. > >>>>> > >>>>> You also need to look at how a 'user' can actually get SCTP to > >>>>> merge data chunks in the first place. > >>>>> > >>>>> With Nagle disabled (and it probably has to be since the data flow > >>>>> is unlikely to be 'command-response' or 'unidirectional bulk') > >>>>> it is currently almost impossible to get more than one chunk > >>>>> into an ethernet frame. > >>>>> > >>>>> Support for MSG_MORE would help. > >>>> What about adding support for the explicit EOR mode as specified in > >>>> https://tools.ietf.org/html/rfc6458#section-8.1.26 > >>> > >>> Seizing the moment to clarify my understanding on that. :) > >>> Such multiple calls to send system calls will result in a single data > >>> chunk. Is that so? That's what I get from that text and also from this > >> No. It results in a single user message. This means you can send > >> a user message larger than the send buffer size. How the user message > >> is fragmented in DATA chunks is transparent to the upper layer. > >> > >> Does this make things clearer? > > > > I think so, yes. So it allows delaying setting the Ending fragment bit > > until the application set SCTP_EOR. All the rest before this stays as > > before: first send() will generate a chunk with Beginning bit set and > > may generate some other middle-fragments (no B nor E bit set) if > > necessary, second to N-1 call to send will generate only middle > > fragments, while the last send, with SCTP_EOF, will then set the Ending > > fragment in the last one. Right? > Yes. But there are no restrictions on the user data provided in send() > calls and DATA chunks. So you can > send(100000 byte, no SCTP_EOR) > resulting in one DATA chunk with the B bit, several with no B and no E bit. > send(100000 byte, no SCTP_EOR) > resulting in several chunks with no B and no E bit. > send(100000 byte, SCTP_EOR) > resulting in several chunks with no B and no E bit and one (the last) chunk > with the E bit. > > On the other hand you can do > send(1 byte, no SCTP_EOR) > resulting in a single DATA chunk with the E bit set. > send(1 byte, no SCTP_EOR) > send(1 byte, no SCTP_EOR) > send(1 byte, no SCTP_EOR) > send(1 byte, no SCTP_EOR) > send(1 byte, no SCTP_EOR) > All resulting in a single DATA chunk with 5 bytes user data and no B or E bit. > (For example if Nagle is enabled and only after the last send call the SACK > arrives). > send(1 byte, SCTP_EOR) > results in a single DATA chunk with the E bist set.
Cool, thanks Michael. It will be quite fun to mix this with MSG_MORE logic, I think :) Best regards, Marcelo
