On 08/10, David Vernet wrote: > On Thu, Aug 10, 2023 at 03:46:18PM -0700, Stanislav Fomichev wrote: > > On 08/10, David Vernet wrote: > > > Currently, if a struct_ops map is loaded with BPF_F_LINK, it must also > > > define the .validate() and .update() callbacks in its corresponding > > > struct bpf_struct_ops in the kernel. Enabling struct_ops link is useful > > > in its own right to ensure that the map is unloaded if an application > > > crashes. For example, with sched_ext, we want to automatically unload > > > the host-wide scheduler if the application crashes. We would likely > > > never support updating elements of a sched_ext struct_ops map, so we'd > > > have to implement these callbacks showing that they _can't_ support > > > element updates just to benefit from the basic lifetime management of > > > struct_ops links. > > > > > > Let's enable struct_ops maps to work with BPF_F_LINK even if they > > > haven't defined these callbacks, by assuming that a struct_ops map > > > element cannot be updated by default. > > > > Any reason this is not part of sched_ext series? As you mention, > > we don't seem to have such users in the three? > > Hi Stanislav, > > The sched_ext series [0] implements these callbacks. See > bpf_scx_update() and bpf_scx_validate(). > > [0]: https://lore.kernel.org/all/20230711011412.100319-13-tj@xxxxxxxxxx/ > > We could add this into that series and remove those callbacks, but this > patch is fixing a UX / API issue with struct_ops links that's not really > relevant to sched_ext. I don't think there's any reason to couple > updating struct_ops map elements with allowing the kernel to manage the > lifetime of struct_ops maps -- just because we only have 1 (non-test) > struct_ops implementation in-tree doesn't mean we shouldn't improve APIs > where it makes sense. > > Thanks, > David Ack. I guess up to you and Martin. Just trying to understand whether I'm missing something or the patch does indeed fix some use-case :-)
