libbpf-tools: fallback to tracefs mount point if debugfs is not mounted

Change-Id: Icab8356f9b43b4f28ad77fa4b21e826f74a25be8
Signed-off-by: Mickey Zhu <[email protected]>

libbpf-tools/trace_helpers.c

@@ -1074,6 +1074,30 @@ bool fentry_can_attach(const char *name, const char *mod)
  return id > 0 && fentry_try_attach(id);
 }
 
+#define DEBUGFS "/sys/kernel/debug/tracing"
+#define TRACEFS "/sys/kernel/tracing"
+
+static bool use_debugfs(void)
+{
+ static int has_debugfs = -1;
+
+ if (has_debugfs < 0)
+ has_debugfs = faccessat(AT_FDCWD, DEBUGFS, F_OK, AT_EACCESS) == 0;
+
+ return has_debugfs == 1;
+}
+
+static const char *tracefs_path(void)
+{
+ return use_debugfs() ? DEBUGFS : TRACEFS;
+}
+
+static const char *tracefs_available_filter_functions(void)
+{
+ return use_debugfs() ? DEBUGFS"/available_filter_functions" :
+ TRACEFS"/available_filter_functions";
+}
+
 bool kprobe_exists(const char *name)
 {
  char addr_range[256];
@@ -1101,7 +1125,7 @@ bool kprobe_exists(const char *name)
  fclose(f);
 
 avail_filter:
- f = fopen("/sys/kernel/debug/tracing/available_filter_functions", "r");
+ f = fopen(tracefs_available_filter_functions(), "r");
  if (!f)
  goto slow_path;
 
@@ -1149,7 +1173,7 @@ bool tracepoint_exists(const char *category, const char *event)
 {
  char path[PATH_MAX];
 
- snprintf(path, sizeof(path), "/sys/kernel/debug/tracing/events/%s/%s/format", category, event);
+ snprintf(path, sizeof(path), "%s/events/%s/%s/format", tracefs_path(), category, event);
  if (!access(path, F_OK))
  return true;
  return false;