[PATCH v4 -tip 1/3] tracing: replace static old_tracer with trace iterator's pointer to the original tracer's name

Currently the trace buffer read functions use a static variable "old_tracer" for detecting if the current tracer changes. This was suitable for a single trace file ("trace"), but to add a snapshot feature that will use the same function for its file, a check against a static variable is not

[PATCH v4 -tip 1/3] tracing: replace static old_tracer with trace iterator's pointer to the original tracer's name

Currently the trace buffer read functions use a static variable old_tracer for detecting if the current tracer changes. This was suitable for a single trace file (trace), but to add a snapshot feature that will use the same function for its file, a check against a static variable is not