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. > > 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.
