On 2025-01-22 13:05:57, Alexandra Winter wrote: > > >On 22.01.25 13:02, Alexandra Winter wrote: >> >> >> On 22.01.25 04:04, Dust Li wrote: >>> On 2025-01-20 11:28:41, Alexandra Winter wrote: >>>> >>>> >>>> On 17.01.25 14:00, Alexandra Winter wrote: >>>>> >>>>> >>>>> On 17.01.25 03:13, Dust Li wrote: >>>>>>>>> Modular Approach: I've made the ism_loopback an independent kernel >>>>>>>>> module since dynamic enable/disable functionality is not yet supported >>>>>>>>> in SMC. Using insmod and rmmod for module management could provide the >>>>>>>>> flexibility needed in practical scenarios. >>>>>>> >>>>>>> With this proposal ism_loopback is just another ism device and SMC-D will >>>>>>> handle removal just like ism_client.remove(ism_dev) of other ism devices. >>>>>>> >>>>>>> But I understand that net/smc/ism_loopback.c today does not provide enable/disable, >>>>>>> which is a big disadvantage, I agree. The ism layer is prepared for dynamic >>>>>>> removal by ism_dev_unregister(). In case of this RFC that would only happen >>>>>>> in case of rmmod ism. Which should be improved. >>>>>>> One way to do that would be a separate ism_loopback kernel module, like you say. >>>>>>> Today ism_loopback is only 10k LOC, so I'd be fine with leaving it in the ism module. >>>>>>> I also think it is a great way for testing any ISM client, so it has benefit for >>>>>>> anybody using the ism module. >>>>>>> Another way would be e.g. an 'enable' entry in the sysfs of the loopback device. >>>>>>> (Once we agree if and how to represent ism devices in genera in sysfs). >>>>>> This works for me as well. I think it would be better to implement this >>>>>> within the common ISM layer, rather than duplicating the code in each >>>>>> device. Similar to how it's done in netdevice. >>>>>> >>>>>> Best regards, >>>>>> Dust >>>>> >>>>> >>>>> Is there a specific example for enable/disable in the netdevice code, you have in mind? >>>>> Or do you mean in general how netdevice provides a common layer? >>>>> Yes, everything that is common for all devices should be provided by the network layer. >>>> >>>> >>>> Dust for some reason, you did not 'Reply-all': >>> >>> Oh, sorry I didn't notice that >>> >>>> Dust Li wrote: >>>>> I think dev_close()/dev_open() are the high-level APIs, while >>>>> ndo_stop()/ndo_open() are the underlying device operations that we >>>>> can reference. >>>> >>>> >>>> I hear you, it can be beneficial to have a way for upper layers to >>>> enable/disable an ism device. >>>> But all this is typically a tricky area. The device driver can also have >>>> reasons to enable/disable a device, then hardware could do that or even >>>> hotplug a device. Error recovery on different levels may want to run a >>>> disable/enable sequence as a reset, etc. And all this has potential for >>>> deadlocks. >>>> All this is rather trivial for ism-loopback, as there is not much of a >>>> lower layer. >>>> ism-vpci already has 'HW' / device driver configure on/off and device >>>> add/remove. >>>> For a future ism-virtio, the Hipervisor may want to add/remove devices. >>>> >>>> I wonder what could be the simplest definition of an enable/disable for >>>> the ism layer, that we can start with? More sophisticated functionality >>>> can always be added later. >>>> Maybe support for add/remove ism-device by the device driver is >>>> sufficient as starting point? >>> >>> I agree; this can be added later. For now, we can simply support >>> unregistering a device from the device driver. Which is already handled >>> by ism_dev_unregister() IIUC. >>> >>> However, I believe we still need an API and the ability to enable or >>> disable ISM devices from the upper layer. For example, if we want to >>> disable a specific ISM device (such as the loopback device) in SMC, we >>> should not do so by disabling the loopback device at the device layer, >>> as it may also serve other clients beyond SMC. >> >> >> Just a thought: not all clients have to use all available ism devices. >> The client could opt out without removing the device. >> >>> >>> Further more, I think removing the loopback from the loopback device >>> driver seems unnecessory ? Since we should support that from the upper >>> layer in the future. > > >If it is not too much effort, I would like to have a simple remove for >ism_loopback soon, as it would allow for simple variations of testcases. Yes, this is very useful for testing before we can do that from the upper layer. > > >>> >>> Best regards, >>> Dust >> >> >> All good points. But it also shows that there are many options how to >> extend ism device handling of the upper layers / clients. >> e.g. I can image a loop macro ism_for_each_dev() might be nice... >> I'd prefer to take one step at a time. Start with a minimal useful ism >> layer and extend by usecase. That works for me. Best regards, Dust
