tracing: Make tracing work when debugfs is not configured in

Currently tracing_init_dentry() returns -ENODEV when debugfs is not
configured in, which causes tracefs not populated with tracing files and
directories, so we will get an empty directory even after we manually
mount tracefs.

We can make tracing_init_dentry() return NULL if debugfs is not
configured in and can manually mount tracefs. But return -ENODEV
if debugfs is configured in but not initialized or failed to create
automount point as that would break backward compatibility with older
tools.

Link: http://lkml.kernel.org/r/1446797056-11683-1-git-send-email-hello.wjx@gmail.com
Signed-off-by: Jiaxing Wang <hello.wjx@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2198a630ef5826a30e51a2974d472b078273f80c..08af79c106e114c284517dfda2708d4f6c36b879 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6847,7 +6847,9 @@ struct dentry *tracing_init_dentry(void)
        if (tr->dir)
                return NULL;
 
-       if (WARN_ON(!debugfs_initialized()))
+       if (WARN_ON(!tracefs_initialized()) ||
+               (IS_ENABLED(CONFIG_DEBUG_FS) &&
+                WARN_ON(!debugfs_initialized())))
                return ERR_PTR(-ENODEV);
 
        /*