> On 29 Jan 2016, at 02:18, Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx> 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.leitner@xxxxxxxxx> wrote: >>> >>> On Thu, Jan 28, 2016 at 06:54:06PM +0100, Michael Tuexen wrote: >>>>> On 28 Jan 2016, at 14:51, David Laight <David.Laight@xxxxxxxxxx> 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. Best regards Michael > > Thanks, > Marcelo > >> >> Best regards >> Michael >>> snippet: >>> "Sending a message using sendmsg() is atomic unless explicit end of >>> record (EOR) marking is enabled on the socket specified by sd (see >>> Section 8.1.26)." >>> >>> Best regards, >>> Marcelo >>> >>>> Best regards >>>> Michael >>>>> >>>>> Given the current implementation you can get almost the required >>>>> behaviour by turning nagle off and on repeatedly. >>>>> >>>>> I did wonder whether the queued data could actually be picked up >>>>> be a Heartbeat chunk that is probing a different remote address >>>>> (which would be bad news). >>>>> >>>>> David >>>>> >>>>> -- >>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in >>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>>>> >>>> >>> >> > -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
