Re: [PATCH 4/4] tracing: Allow boot instances to have snapshot buffers

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

Add to ftrace_boot_snapshot, "=<instance>" name, where the instance will
get a snapshot buffer, and will take a snapshot at the end of boot (which
will save the boot traces).

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 .../admin-guide/kernel-parameters.txt         |  9 +++
 kernel/trace/trace.c                          | 77 +++++++++++++++++--
 2 files changed, 79 insertions(+), 7 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 7a7f41652719..f4e87b17427f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt

@@ -1532,6 +1532,15 @@
 			boot up that is likely to be overridden by user space
 			start up functionality.
 
+			Optionally, the snapshot can also be defined for a tracing
+			instance that was created by the trace_instance= command
+			line parameter.
+
+			trace_instance=foo,sched_switch ftrace_boot_snapshot=foo
+
+			The above will cause the "foo" tracing instance to trigger
+			a snapshot at the end of boot up.
+
 	ftrace_dump_on_oops[=orig_cpu]
 			[FTRACE] will dump the trace buffers on oops.
 			If no parameter is passed, ftrace will dump

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 3cb9bbc0f076..d445789dc247 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c

@@ -192,6 +192,9 @@ static bool snapshot_at_boot;
 static char boot_instance_info[COMMAND_LINE_SIZE] __initdata;
 static int boot_instance_index;
 
+static char boot_snapshot_info[COMMAND_LINE_SIZE] __initdata;

+static int boot_snapshot_index;
+
 static int __init set_cmdline_ftrace(char *str)
 {
 	strlcpy(bootup_tracer_buf, str, MAX_TRACER_SIZE);

@@ -228,9 +231,22 @@ __setup("traceoff_on_warning", stop_trace_on_warning);
 
 static int __init boot_alloc_snapshot(char *str)
 {
-	allocate_snapshot = true;
-	/* We also need the main ring buffer expanded */
-	ring_buffer_expanded = true;
+	char *slot = boot_snapshot_info + boot_snapshot_index;
+	int left = COMMAND_LINE_SIZE - boot_snapshot_index;