tracing/ftrace: add the boot tracer

Add the boot/initcall tracer.

It's primary purpose is to be able to trace the initcalls.

It is intended to be used with scripts/bootgraph.pl after some small
improvements.

Note that it is not active after its init. To avoid tracing (and so
crashing) before the whole tracing engine init, you have to explicitly
call start_boot_trace() after do_pre_smp_initcalls() to enable it.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace.h

@@ -6,6 +6,7 @@
 #include <linux/sched.h>
 #include <linux/clocksource.h>
 #include <linux/mmiotrace.h>
+#include <linux/ftrace.h>
 
 enum trace_type {
 	__TRACE_FIRST_TYPE = 0,
@@ -19,6 +20,7 @@ enum trace_type {
 	TRACE_SPECIAL,
 	TRACE_MMIO_RW,
 	TRACE_MMIO_MAP,
+	TRACE_BOOT,
 
 	__TRACE_LAST_TYPE
 };
@@ -30,6 +32,7 @@ struct ftrace_entry {
 	unsigned long		ip;
 	unsigned long		parent_ip;
 };
+extern struct tracer boot_tracer;
 
 /*
  * Context switch trace entry - which task (and prio) we switched from/to:
@@ -108,6 +111,7 @@ struct trace_field {
 		struct print_entry		print;
 		struct mmiotrace_rw		mmiorw;
 		struct mmiotrace_map		mmiomap;
+		struct boot_trace		initcall;
 	};
 };
 

kernel/trace/trace_boot.c

@@ -0,0 +1,101 @@
+/*
+ * ring buffer based initcalls tracer
+ *
+ * Copyright (C) 2008 Frederic Weisbecker <fweisbec@gmail.com>
+ *
+ */
+
+#include <linux/init.h>
+#include <linux/debugfs.h>
+#include <linux/ftrace.h>
+
+#include "trace.h"
+
+static struct trace_array *boot_trace;
+static int trace_boot_enabled;
+
+
+/* Should be started after do_pre_smp_initcalls() in init/main.c */
+void start_boot_trace(void)
+{
+	trace_boot_enabled = 1;
+}
+
+void stop_boot_trace(struct trace_array *tr)
+{
+	trace_boot_enabled = 0;
+}
+
+static void boot_trace_init(struct trace_array *tr)
+{
+	int cpu;
+	boot_trace = tr;
+
+	trace_boot_enabled = 0;
+
+	for_each_cpu_mask(cpu, cpu_possible_map)
+		tracing_reset(tr->data[cpu]);
+}
+
+static void boot_trace_ctrl_update(struct trace_array *tr)
+{
+	if (tr->ctrl)
+		start_boot_trace();
+	else
+		stop_boot_trace(tr);
+}
+
+static int initcall_print_line(struct trace_iterator *iter)
+{
+	int ret = 1;
+	struct trace_entry *entry = iter->ent;
+	struct boot_trace *it = &entry->field.initcall;
+	struct trace_seq *s = &iter->seq;
+
+	if (iter->ent->type == TRACE_BOOT)
+		ret = trace_seq_printf(s, "%pF called from %i "
+				       "returned %d after %lld msecs\n",
+				       it->func, it->caller, it->result,
+				       it->duration);
+	if (ret)
+		return 1;
+	return 0;
+}
+
+struct tracer boot_tracer __read_mostly =
+{
+	.name		= "initcall",
+	.init		= boot_trace_init,
+	.reset		= stop_boot_trace,
+	.ctrl_update	= boot_trace_ctrl_update,
+	.print_line	= initcall_print_line,
+};
+
+
+void trace_boot(struct boot_trace *it)
+{
+	struct trace_entry *entry;
+	struct trace_array_cpu *data;
+	unsigned long irq_flags;
+	struct trace_array *tr = boot_trace;
+
+	if (!trace_boot_enabled)
+		return;
+
+	preempt_disable();
+	data = tr->data[smp_processor_id()];
+
+	raw_local_irq_save(irq_flags);
+	__raw_spin_lock(&data->lock);
+
+	entry = tracing_get_trace_entry(tr, data);
+	tracing_generic_entry_update(entry, 0);
+	entry->type = TRACE_BOOT;
+	entry->field.initcall = *it;
+
+	__raw_spin_unlock(&data->lock);
+	raw_local_irq_restore(irq_flags);
+	trace_wake_up();
+
+	preempt_enable();
+}