On Thu, May 20, 2021 at 01:16:38AM +0200, Michael Tuexen wrote: > > On 20. May 2021, at 00:44, mleitner@xxxxxxxxxx wrote: > > > > On Wed, May 19, 2021 at 02:44:20PM -0400, Xin Long wrote: > >> On Wed, May 19, 2021 at 2:15 PM Michael Tuexen <tuexen@xxxxxxxxxxx> wrote: > >>> > >>>> On 19. May 2021, at 18:18, Xin Long <lucien.xin@xxxxxxxxx> wrote: > >>>> > >>>> On Tue, May 18, 2021 at 2:33 PM Xin Long <lucien.xin@xxxxxxxxx> wrote: > >>>>> > >>>>> On Tue, May 18, 2021 at 1:38 PM Michael Tuexen <tuexen@xxxxxxxxxxx> wrote: > >>>>>> > >>>>>>> On 18. May 2021, at 18:43, Xin Long <lucien.xin@xxxxxxxxx> wrote: > >>>>>>> > >>>>>>> Hi, Michael, > >>>>>>> > >>>>>>> We're implementing RFC8899 (PLPMTUD) on Linux SCTP recently, > >>>>>>> and to make this be controlled by setsockopt with > >>>>>>> SCTP_PEER_ADDR_PARAMS, as in > >>>>>>> > >>>>>>> https://datatracker.ietf.org/doc/html/rfc6458#section-8.1.12: > >>>>>>> > >>>>>>> we need another two flags to add for spp_flags: > >>>>>>> > >>>>>>> SPP_PLPMTUD_ENABLE > >>>>>>> SPP_PLPMTUD_DISABLE > >>>>>>> > >>>>>>> Do you think it makes sense? if yes, does the RFC6458 need to update? > >>>>>>> if not, do you have a better suggestion for it? > >>>>>> It is great new that you want to implement RFC 8899. I plan to do the > >>>>>> same for the FreeBSD stack. > >>>>>> > >>>>>> In my view, RFC 8899 is the right way to implement PMTU discovery. > >>>>>> So I will just use the SPP_PMTUD_ENABLE and SPP_PMTUD_DISABLE. I don't > >>>>>> think that the user needs to control which method is used. > >>>>>> I you want to support multiple versions, I would make that > >>>>>> controllable via a sysctl variable. But I think for FreeBSD, support > >>>>>> for RFC 8899 will be the only way of doing PMTU discovery. There > >>>>>> might be multiple choices for details like how to do the searching, > >>>>>> how long to wait for some events. These will be controllable via > >>>>>> sysctl. > >>>>>> > >>>>>> So in my view, there is no need to extend the socket API. What do you think? > >>>> I just noticed that with multiple versions supported, and without extending > >>>> this API, all applications will have to use the same version as it's > >>>> controlled by > >>>> sysctl. And when switching to another version by sysctl, all > >>>> applications will be > >>>> affected and have to do the switch. that seems not nice. > >>> That is true, but an application can not expect any specific behaviour > >>> right now when they are not disabling PMTUD. > >>> > >>> What about adding a sysctl variable, which defines the default > >>> algorithm and a socket option, which allows to get and set > >>> the algorithm being used. > >> yes, that's also what I'm thinking. > > > > +1 > > > >> sysctl is always used for the default value for future sockets. > >> and the socket option should be added for a socket/asoc's setting. > > > > Speaking of inheritance, it should also use the SCTP_FUTURE_ASSOC / > > SCTP_CURRENT_ASSOC / SCTP_ALL_ASSOC mechanism. Like > > SCTP_PEER_ADDR_PARAMS, for example. > Yepp. > > > > The system can provide defaults but if the application requires > > something, it should have a good way of requesting it. > > > > Speaking of SCTP_PEER_ADDR_PARAMS, maybe reuse spp_pathmtu field? > > As in, if SPP_PMTUD_ENABLE is enabled, spp_pathmtu of "1" or "2" bytes > > doesn't make sense, and it could mean the algorithm used. Thing is, > > the field is currently ignored, and it could lead to some unexpected > > behavior change. It's probably safer to just add another sockopt, but > > wanted to share the idea anyway. > I leave it completely up to you what you implement in Linux. But I > would prefer to use a separate socket option instead of overloading > an existing one. Wait. Somehow I thought we were talking about extending the RFC with these new definitions here, no? Or at least agreeing on a common interface. It would be beneficial for the application to be able to use the same API on FreeBSD or Linux. Thanks, Marcelo > > Best regards > Michael > > > >> > >> SCTP_PTMUD_METHOD? > > > > s/PTMUD/PMTUD/ :-) > > > >> 0: PTB one > >> 1. PLPMTUD > >> > >>> > >>> Best regards > >>> Michael > >>>> > >>>>> OK, that makes sense to me. > >>>>> > >>>>> Another thing I want to know your opinion on is: do you think the HB > >>>>> should be created > >>>>> separately for PLPMTUD probe, instead of reusing the old HB that > >>>>> checks the link connectivity? > >>>>> As the HB for PLPMTUD probe might get lost, which we don't want to > >>>>> affect the link's > >>>>> connectivity. > >>>>> > >>>>>> > >>>>>> Best regards > >>>>>> Michael > >>>>>>> > >>>>>>> Thanks. > >>>>>> > >>> > >> > > >
