tracing: Add snapshot feature to instances

Add the "snapshot" file to the the multi-buffer instances.

  cd /sys/kernel/debug/tracing/instances
  mkdir foo
  ls foo
buffer_size_kb  buffer_total_size_kb  events  free_buffer  set_event
snapshot  trace  trace_clock  trace_marker  trace_options  trace_pipe
tracing_on
  cat foo/snapshot
 # tracer: nop
 #
 #
 # * Snapshot is freed *
 #
 # Snapshot commands:
 # echo 0 > snapshot : Clears and frees snapshot buffer
 # echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.
 #                      Takes a snapshot of the main buffer.
 # echo 2 > snapshot : Clears snapshot buffer (but does not allocate)
 #                      (Doesn't have to be '2' works with any number that
 #                       is not a '0' or '1')
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -4302,9 +4302,9 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
 		local_irq_disable();
 		/* Now, we're going to swap */
 		if (iter->cpu_file == RING_BUFFER_ALL_CPUS)
-			update_max_tr(&global_trace, current, smp_processor_id());
+			update_max_tr(tr, current, smp_processor_id());
 		else
-			update_max_tr_single(&global_trace, current, iter->cpu_file);
+			update_max_tr_single(tr, current, iter->cpu_file);
 		local_irq_enable();
 		break;
 	default:
@@ -5533,6 +5533,11 @@ init_tracer_debugfs(struct trace_array *tr, struct dentry *d_tracer)
 
 	trace_create_file("tracing_on", 0644, d_tracer,
 			    tr, &rb_simple_fops);
+
+#ifdef CONFIG_TRACER_SNAPSHOT
+	trace_create_file("snapshot", 0644, d_tracer,
+			  (void *)&tr->trace_cpu, &snapshot_fops);
+#endif
 }
 
 static __init int tracer_init_debugfs(void)
@@ -5574,11 +5579,6 @@ static __init int tracer_init_debugfs(void)
 			&ftrace_update_tot_cnt, &tracing_dyn_info_fops);
 #endif
 
-#ifdef CONFIG_TRACER_SNAPSHOT
-	trace_create_file("snapshot", 0644, d_tracer,
-			  (void *)&global_trace.trace_cpu, &snapshot_fops);
-#endif
-
 	create_trace_instances(d_tracer);
 
 	create_trace_options_dir(&global_trace);