On Wed, 7 Jan 2026 11:41:33 -0500
Steven Rostedt [off-list ref] wrote:

quoted

@@ -4888,6 +4888,9 @@ static int tracing_open(struct inode *inode, struct file *file)
 		int cpu = tracing_get_cpu(inode);
 		struct array_buffer *trace_buf = &tr->array_buffer;
 
+		if (trace_array_is_readonly(tr))
+			return -EPERM;

So this fails if someone opens a file in RDONLY mode?

Why?

This is for `trace` file and this block is to erase the buffer.

 -----
	/* If this file was open for write, then erase contents */
	if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) {
		int cpu = tracing_get_cpu(inode);
		struct array_buffer *trace_buf = &tr->array_buffer;

		if (trace_array_is_readonly(tr))
			return -EPERM;
 -----

Thus, if user opens it RDONLY mode to read the buffer, we don't care
because it is readonly (readable).

Thank you,

-- 
Masami Hiramatsu (Google) [off-list ref]