On Tue, 21 Jul 2020 12:31:30 -0700 Sean Christopherson <[email protected]> wrote:
> +Steve > > Background: KVM has two tracepoints that effectively trace the same thing > (VM-Exit vs. nested VM-Exit), but use completely different formatting and > nomenclature for each of the existing tracepoints. I want to add a common > macro to create the tracepoints so that they capture the exact same info > and report it with the exact same format. But that means breaking the > "ABI" for one of the tracepoints, e.g. trace-cmd barfs on the rename of > exit_code to exit_reason. Feel free to update it. > > Was there ever a verdict on whether or not tracepoints are considered ABI > and thus must retain backwards compatibility? > > If not, what's the proper way to upstream changes to trace-cmd? > There's a kvm plugin in the libtraceevent code. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/lib/traceevent/plugins/plugin_kvm.c This overrides how the events are read. In the callback handler (e.g. kvm_nested_vmexit_handle()), you can test if "rip" is there or not. If it is not, you can do something different. For example: struct tep_format_field *field; field = tep_find_any_field(event, "rip"); if (field) { tep_print_num_field(s, "rip %llx ", event, "rip", record, 1) [..] } else { /* do something new */ } You can test if fields exist and have the plugins do different things depending on the format of an event. This is what I do in case an event changes in the future. -- Steve
