tools/virtio: use canonical ftrace path

The canonical location for the tracefs filesystem is at /sys/kernel/tracing.

But, from Documentation/trace/ftrace.rst:

  Before 4.1, all ftrace tracing control files were within the debugfs
  file system, which is typically located at /sys/kernel/debug/tracing.
  For backward compatibility, when mounting the debugfs file system,
  the tracefs file system will be automatically mounted at:

  /sys/kernel/debug/tracing

A few spots in tools/virtio still refer to this older debugfs
path, so let's update them to avoid confusion.

Signed-off-by: Ross Zwisler <zwisler@google.com>
Message-Id: <20230215223350.2658616-6-zwisler@google.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Mukesh Ojha <quic_mojha@quicinc.com>

diff --git a/tools/virtio/virtio-trace/README b/tools/virtio/virtio-trace/README
index 4fb9368..0127ff0 100644 (file)
--- a/tools/virtio/virtio-trace/README
+++ b/tools/virtio/virtio-trace/README
@@ -95,7 +95,7 @@ Run
 
 1) Enable ftrace in the guest
  <Example>
-       # echo 1 > /sys/kernel/debug/tracing/events/sched/enable
+       # echo 1 > /sys/kernel/tracing/events/sched/enable
 
 2) Run trace agent in the guest
  This agent must be operated as root.

diff --git a/tools/virtio/virtio-trace/trace-agent.c b/tools/virtio/virtio-trace/trace-agent.c
index cdfe77c..7e2d9bb 100644 (file)
--- a/tools/virtio/virtio-trace/trace-agent.c
+++ b/tools/virtio/virtio-trace/trace-agent.c
@@ -18,8 +18,9 @@
 #define PIPE_DEF_BUFS          16
 #define PIPE_MIN_SIZE          (PAGE_SIZE*PIPE_DEF_BUFS)
 #define PIPE_MAX_SIZE          (1024*1024)
-#define READ_PATH_FMT  \
-               "/sys/kernel/debug/tracing/per_cpu/cpu%d/trace_pipe_raw"
+#define TRACEFS                "/sys/kernel/tracing"
+#define DEBUGFS                "/sys/kernel/debug/tracing"
+#define READ_PATH_FMT          "%s/per_cpu/cpu%d/trace_pipe_raw"
 #define WRITE_PATH_FMT         "/dev/virtio-ports/trace-path-cpu%d"
 #define CTL_PATH               "/dev/virtio-ports/agent-ctl-path"
 
@@ -120,9 +121,12 @@ static const char *make_path(int cpu_num, bool this_is_write_path)
        if (this_is_write_path)
                /* write(output) path */
                ret = snprintf(buf, PATH_MAX, WRITE_PATH_FMT, cpu_num);
-       else
+       else {
                /* read(input) path */
-               ret = snprintf(buf, PATH_MAX, READ_PATH_FMT, cpu_num);
+               ret = snprintf(buf, PATH_MAX, READ_PATH_FMT, TRACEFS, cpu_num);
+               if (ret > 0 && access(buf, F_OK) != 0)
+                       ret = snprintf(buf, PATH_MAX, READ_PATH_FMT, DEBUGFS, cpu_num);
+       }
 
        if (ret <= 0) {
                pr_err("Failed to generate %s path(CPU#%d):%d\n",