On 09.04.24 03:44, Wen Gu wrote: > > > On 2024/4/4 23:15, Niklas Schnelle wrote: >> On Thu, 2024-04-04 at 21:12 +0800, Wen Gu wrote: >>> >>> On 2024/4/4 19:42, Niklas Schnelle wrote: >>>> On Thu, 2024-04-04 at 17:32 +0800, Wen Gu wrote: >>>>> >>>>> On 2024/4/4 00:25, Gerd Bayer wrote: >>>>>> On Sun, 2024-03-24 at 21:55 +0800, Wen Gu wrote: >>>>>>> This implements some operations that loopback-ism does not support >>>>>>> currently: >>>>>>> - vlan operations, since there is no strong use-case for it. >>>>>>> - signal_event operations, since there is no event to be processed >>>>>>> by the loopback-ism device. >>>>>> >>>>>> Hi Wen, >>>>>> >>>>>> I wonder if the these operations that are not supported by loopback-ism >>>>>> should rather be marked "optional" in the struct smcd_ops, and the >>>>>> calling code should call these only when they are implemented. >>>>>> >>>>>> Of course this would mean more changes to net/smc/smc_core.c - but >>>>>> loopback-ism could omit these "boiler-plate" functions. >>>>>> >>>>> >>>>> Hi Gerd. >>>>> >>>>> Thank you for the thoughts! I agree that checks like 'if(smcd->ops->xxx)' >>>>> can avoid the device driver from implementing unsupported operations. But I >>>>> am afraid that which operations need to be defined as 'optional' may differ >>>>> from different device perspectives (e.g. for loopback-ism they are vlan-related >>>>> opts and signal_event). So I perfer to simply let the smc protocol assume >>>>> that all operations have been implemented, and let drivers to decide which >>>>> ones are unsupported in implementation. What do you think? >>>>> >>>>> Thanks! >>>>> >>>> >>>> I agree with Gerd, in my opinion it is better to document ops as >>>> optional and then allow their function pointers to be NULL and check >>>> for that. Acting like they are supported and then they turn out to be >>>> nops to me seems to contradict the principle of least surprises. I also >>>> think we can find a subset of mandatory ops without which SMC-D is >>>> impossible and then everything else should be optional. >>> >>> I see. If we all agree to classify smcd_ops into mandatory and optional ones, >>> I'll add a patch to mark the optional ops and check if they are implemented. >> >> Keep in mind I don't speak for the SMC maintainers but that does sound >> reasonable to me. >> > > Hi Wenjia and Jan, do you have any comments on this and [1]? Thanks! > > [1] https://lore.kernel.org/netdev/60b4aec0b4bf4474d651b653c86c280dafc4518a.camel@xxxxxxxxxxxxx/ > >>> >>>> >>>> As a first guess I think the following options may be mandatory: >>>> >>>> * query_remote_gid() >>>> * register_dmb()/unregister_dmb() >>>> * move_data() >>>> For this one could argue that either move_data() or >>>> attach_dmb()/detach_dmb() is required though personally I would >>>> prefer to always have move_data() as a fallback and simple API >>>> * supports_v2() >>>> * get_local_gid() >>>> * get_chid() >>>> * get_dev() >>> I agree with this classification. Just one point, maybe we can take >>> supports_v2() as an optional ops, like support_dmb_nocopy()? e.g. if >>> it is not implemented, we treat it as an ISMv1. >>> >>> Thanks! >> >> Interpreting a NULL supports_v2() as not supporting v2 sounds >> reasonable to me. > Let me add my thoughts to the discussion: For the vlan operations and signal_event operations that loopback-ism does not support: I like the idea to set the ops to NULL and make sure the caller checks that and can live with it. That is readable and efficient. I don't think there is a need to discuss a strategy now, which ops could be optional in the future. This is all inside the kernel. loopback-ism is even inside the smc module. Such comments in the code get outdated very easily. I would propose to mark those as optional struct smcd_ops, where all callers can handle a NULL pointer and still be productive. Future support of other devices for SMC-D can update that.
