Hi Steven, Thanks for sharing your experience!
On Fri, Aug 7, 2026 at 5:43 AM Steven Rostedt <[email protected]> wrote: > > On Fri, 7 Aug 2026 00:17:27 -0700 > Song Liu <[email protected]> wrote: [...] > #!/bin/sh > # SPDX-License-Identifier: GPL-2.0 > # description: event filter function - test event filtering on functions > # requires: set_event events/kmem/kmem_cache_free/filter > # flags: instance > > If "set_event" or "events/kmem/kmem_cache_free/filter" does not exist, the > test will be skipped. Hmm.. If a bug somehow causes set_event to disappear, this test will be skipped by accident, no? These types of bugs are not common though. > > > 2) It delays the actual deprecation of a feature. IOW, the feature will > > somehow stays in the selftests for much longer time. > > We do not deprecate features. tracefs code is user API. We do not break > user space. The ftrace_enabled is something that is being removed because > it is broken to begin with. In fact, if we find out that anything depends > on ftrace_enabled, we need to revert the change that disabled it. > > The removal of ftrace_enabled is the exception and not the rule. Agreed that ftrace APIs need to be very stable, as there are many out of tree users. OTOH, I think livepatch can afford breaking some compatibility. > > Overall, I think requiring backward compatibility appears to be > > attractive when we go from "having very little selftests" to > > "having some selftest coverage". However, not requiring backward > > compatibility will help us achieve better test coverage in the long run. > > The ftrace selftest requirements are different than the BPF requirements. > We have been supporting this since 2014 without issue. And have actually > found making things backward compatible helpful. We are not going to change > that. With mature selftests, I guess testing LTS kernels with the selftests shipped with them is still a valid option? I guess this is up to the folks who run these tests. In this specific case, given the logic is not that complex, I agree we can maintain the compatibility, Thanks, Song
