trace: don't abort qemu if ftrace can't be initialized

If the ftrace backend is compiled into QEMU, any attempt to start QEMU while non-root will fail due to the inability to open /sys/kernel/debug/tracing/tracing_on. Add a fallback into the code so that it connects up the trace_marker_fd variable to /dev/null when getting EACCES on the 'trace_on' file. This allows QEMU to run, with ftrace turned into a no-op. [Fixed s/setting/getting/ and s/EACCESS/EACCES/ errors pointed out by Eric Blake <[email protected]>. --Stefan] Signed-off-by: Daniel P. Berrange <[email protected]> Message-id: [email protected] Signed-off-by: Stefan Hajnoczi <[email protected]>
xiaolou86 · Oct 12, 2016 · 8ed5372 · 8ed5372
1 parent 7f1b588
commit 8ed5372
Showing 1 changed file with 6 additions and 0 deletions.
diff --git a/trace/ftrace.c b/trace/ftrace.c
@@ -51,6 +51,12 @@ bool ftrace_init(void)
         snprintf(path, PATH_MAX, "%s/tracing/tracing_on", debugfs);
         trace_fd = open(path, O_WRONLY);
         if (trace_fd < 0) {
+            if (errno == EACCES) {
+                trace_marker_fd = open("/dev/null", O_WRONLY);
+                if (trace_marker_fd != -1) {
+                    return true;
+                }
+            }
             perror("Could not open ftrace 'tracing_on' file");
             return false;
         } else {