Commit d8741e2e authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Steven Rostedt
Browse files

tracing: Add help of snapshot feature when snapshot is empty 



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: default avatarHiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent a335358f

kernel/trace/trace.c

+24 −1
Original line number 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");

}



#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)

{

	struct trace_iterator *iter = v;
@@ -2411,7 +2432,9 @@ static int s_show(struct seq_file *m, void *v) 
			seq_puts(m, "#\n");

			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);

		else

			trace_default_header(m);