tracing: Add help of snapshot feature when snapshot is empty (d8741e2e) · Commits · 戴 / test

When cat'ing the snapshot file, instead of showing an empty trace header like the trace file does, show how to use the snapshot feature. Also, this is a good place to show if the snapshot has been allocated or not. Users may want to "pre allocate" the snapshot to have a fast "swap" of the current buffer. Otherwise, a swap would be slow and might fail as it would need to allocate the snapshot buffer, and that might fail under tight memory constraints. Here's what it looked like before: # tracer: nop # # entries-in-buffer/entries-written: 0/0 #P:4 # # _-----=> irqs-off # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / delay # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | Here's what it looks like now: # 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') Acked-by:

Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com> Signed-off-by:

Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

+24 −1

Original line number	Original line	Diff line number	Diff line
	@@ -2400,6 +2400,27 @@ static void test_ftrace_alive(struct seq_file *m)
	seq_printf(m, "# MAY BE MISSING FUNCTION EVENTS\n");		seq_printf(m, "# MAY BE MISSING FUNCTION EVENTS\n");
	}		}

			#ifdef CONFIG_TRACER_MAX_TRACE
			static void print_snapshot_help(struct seq_file m, struct trace_iterator iter)
			{
			if (iter->trace->allocated_snapshot)
			seq_printf(m, "#\n# * Snapshot is allocated *\n#\n");
			else
			seq_printf(m, "#\n# * Snapshot is freed *\n#\n");

			seq_printf(m, "# Snapshot commands:\n");
			seq_printf(m, "# echo 0 > snapshot : Clears and frees snapshot buffer\n");
			seq_printf(m, "# echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.\n");
			seq_printf(m, "# Takes a snapshot of the main buffer.\n");
			seq_printf(m, "# echo 2 > snapshot : Clears snapshot buffer (but does not allocate)\n");
			seq_printf(m, "# (Doesn't have to be '2' works with any number that\n");
			seq_printf(m, "# is not a '0' or '1')\n");
			}
			#else
			/* Should never be called */
			static inline void print_snapshot_help(struct seq_file m, struct trace_iterator iter) { }
			#endif

	static int s_show(struct seq_file m, void v)		static int s_show(struct seq_file m, void v)
	{		{
	struct trace_iterator *iter = v;		struct trace_iterator *iter = v;
	@@ -2411,7 +2432,9 @@ static int s_show(struct seq_file m, void v)
	seq_puts(m, "#\n");		seq_puts(m, "#\n");
	test_ftrace_alive(m);		test_ftrace_alive(m);
	}		}
	if (iter->trace && iter->trace->print_header)		if (iter->snapshot && trace_empty(iter))
			print_snapshot_help(m, iter);
			else if (iter->trace && iter->trace->print_header)
	iter->trace->print_header(m);		iter->trace->print_header(m);
	else		else
	trace_default_header(m);		trace_default_header(m);

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