rtla/tests: Test BPF action program

Add a test that implements a BPF program writing to a test map, which
is attached to RTLA via --bpf-action to be executed on theshold
overflow.

A combination of --on-threshold shell with bpftool (which is always
present if BPF support is enabled) is used to check whether the BPF
program has executed successfully.

Suggested-by: Crystal Wood <crwood@redhat.com>
Link: https://lore.kernel.org/r/20251126144205.331954-5-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>

Author: lenticularis39

tools/tracing/rtla/Makefile

@@ -76,12 +76,18 @@ src/timerlat.skel.h: src/timerlat.bpf.o
 
 example/timerlat_bpf_action.o: example/timerlat_bpf_action.c
 	$(QUIET_CLANG)$(CLANG) -g -O2 -target bpf -c $(filter %.c,$^) -o $@
+
+tests/bpf/bpf_action_map.o: tests/bpf/bpf_action_map.c
+	$(QUIET_CLANG)$(CLANG) -g -O2 -target bpf -c $(filter %.c,$^) -o $@
 else
 src/timerlat.skel.h:
 	$(Q)echo '/* BPF skeleton is disabled */' > src/timerlat.skel.h
 
 example/timerlat_bpf_action.o: example/timerlat_bpf_action.c
 	$(Q)echo "BPF skeleton support is disabled, skipping example/timerlat_bpf_action.o"
+
+tests/bpf/bpf_action_map.o: tests/bpf/bpf_action_map.c
+	$(Q)echo "BPF skeleton support is disabled, skipping tests/bpf/bpf_action_map.o"
 endif
 
 $(RTLA): $(RTLA_IN)
@@ -103,7 +109,7 @@ clean: doc_clean fixdep-clean
 	$(Q)rm -f rtla rtla-static fixdep FEATURE-DUMP rtla-*
 	$(Q)rm -rf feature
 	$(Q)rm -f src/timerlat.bpf.o src/timerlat.skel.h example/timerlat_bpf_action.o
-check: $(RTLA)
-	RTLA=$(RTLA) prove -o -f tests/
+check: $(RTLA) tests/bpf/bpf_action_map.o
+	RTLA=$(RTLA) BPFTOOL=$(SYSTEM_BPFTOOL) prove -o -f tests/
 examples: example/timerlat_bpf_action.o
 .PHONY: FORCE clean check

tools/tracing/rtla/tests/bpf/bpf_action_map.c

@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_tracing.h>
+
+char LICENSE[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, unsigned int);
+	__type(value, unsigned long long);
+} rtla_test_map SEC(".maps");
+
+struct trace_event_raw_timerlat_sample;
+
+SEC("tp/timerlat_action")
+int action_handler(struct trace_event_raw_timerlat_sample *tp_args)
+{
+	unsigned int key = 0;
+	unsigned long long value = 42;
+
+	bpf_map_update_elem(&rtla_test_map, &key, &value, BPF_ANY);
+
+	return 0;
+}

tools/tracing/rtla/tests/timerlat.t

@@ -67,6 +67,21 @@ check "hist with trace output at end" \
 	"timerlat hist -d 1s --on-end trace" 0 "^  Saving trace to timerlat_trace.txt$"
 check "top with trace output at end" \
 	"timerlat top -d 1s --on-end trace" 0 "^  Saving trace to timerlat_trace.txt$"
+
+# BPF action program tests
+if [ "$option" -eq 0 ]
+then
+	# Test BPF action program properly in BPF mode
+	[ -z "$BPFTOOL" ] && BPFTOOL=bpftool
+	check "hist with BPF action program (BPF mode)" \
+		"timerlat hist -T 2 --bpf-action tests/bpf/bpf_action_map.o --on-threshold shell,command='$BPFTOOL map dump name rtla_test_map'" \
+		2 '"value": 42'
+else
+	# Test BPF action program failure in non-BPF mode
+	check "hist with BPF action program (non-BPF mode)" \
+		"timerlat hist -T 2 --bpf-action tests/bpf/bpf_action_map.o" \
+		1 "BPF actions are not supported in tracefs-only mode"
+fi
 done
 
 test_end