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 setting
EACCESS on the 'trace_on' file. This allows QEMU to
run, with ftrace turned into a no-op.
Signed-off-by: Daniel P. Berrange <berra...@redhat.com>
---
trace/ftrace.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/trace/ftrace.c b/trace/ftrace.c
index e953922..3588bb0 100644
--- 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 {
--
2.7.4
