This patch implements all logic necessary to match a new trace event that we add against preserved trace events from kho. If we find a match, we give the new trace event the old event's identifier. That way, trace read-outs are able to make sense of buffer contents again because the parsing code for events looks at the same identifiers.
Signed-off-by: Alexander Graf <[email protected]> --- kernel/trace/trace_output.c | 65 ++++++++++++++++++++++++++++++++++++- 1 file changed, 64 insertions(+), 1 deletion(-) diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c index 113de40c616f..d2e2a6346322 100644 --- a/kernel/trace/trace_output.c +++ b/kernel/trace/trace_output.c @@ -749,6 +749,67 @@ void trace_event_read_unlock(void) up_read(&trace_event_sem); } +/** + * trace_kho_fill_event_type - restore event type info from KHO + * @event: the event type to enumerate + * + * Event types are semi-dynamically generated. To ensure that + * their identifiers match before and after kexec with KHO, + * let's match up unique name identifiers and fill in the + * respective ID information if we booted with KHO. + */ +static bool trace_kho_fill_event_type(struct trace_event *event) +{ +#ifdef CONFIG_FTRACE_KHO + const char *path = "/ftrace/events"; + void *fdt = kho_get_fdt(); + int err, len, off, id; + const void *p; + + if (!fdt) + return false; + + if (WARN_ON(!event->name)) + return false; + + pr_debug("Trying to revive event '%s'", event->name); + + off = fdt_path_offset(fdt, path); + if (off < 0) { + pr_debug("Could not find '%s' in DT", path); + return false; + } + + err = fdt_node_check_compatible(fdt, off, "ftrace,events-v1"); + if (err) { + pr_warn("Node '%s' has invalid compatible", path); + return false; + } + + p = fdt_getprop(fdt, off, event->name, &len); + if (!p) { + pr_warn("Event '%s' not found", event->name); + return false; + } + + if (len != sizeof(event->type)) { + pr_warn("Event '%s' has invalid length", event->name); + return false; + } + + id = *(const u32 *)p; + + /* Mark ID as in use */ + if (ida_alloc_range(&trace_event_ida, id, id, GFP_KERNEL) != id) + return false; + + event->type = id; + return true; +#endif + + return false; +} + /** * register_trace_event - register output for an event type * @event: the event type to register @@ -777,7 +838,9 @@ int register_trace_event(struct trace_event *event) if (WARN_ON(!event->funcs)) goto out; - if (!event->type) { + if (trace_kho_fill_event_type(event)) { + pr_debug("Recovered '%s' as id=%d", event->name, event->type); + } else if (!event->type) { event->type = alloc_trace_event_type(); if (!event->type) goto out; -- 2.40.1 Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879
