From a64035fd07135e0de1c66228c4b637858261b78f Mon Sep 17 00:00:00 2001
From: Steven Rostedt <srostedt@redhat.com>
Date: Fri, 4 Sep 2009 14:24:40 -0400
Subject: [PATCH] --- yaml --- r: 158494 b: refs/heads/master c:
 85bac32c4a52c592b857f2c360cc5ec93a097d70 h: refs/heads/master v: v3

---
 [refs]                            | 2 +-
 trunk/include/linux/ring_buffer.h | 9 +++++++++
 trunk/kernel/trace/Kconfig        | 8 ++++++++
 trunk/kernel/trace/ring_buffer.c  | 4 ++++
 4 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/[refs] b/[refs]
index de3d1ff51112..7d47b7d20a37 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 62f0b3eb5cb58931a02ee4e599e19c80a171e351
+refs/heads/master: 85bac32c4a52c592b857f2c360cc5ec93a097d70
diff --git a/trunk/include/linux/ring_buffer.h b/trunk/include/linux/ring_buffer.h
index e061b4ecdc3a..5fcc31ed5771 100644
--- a/trunk/include/linux/ring_buffer.h
+++ b/trunk/include/linux/ring_buffer.h
@@ -140,8 +140,17 @@ unsigned long ring_buffer_size(struct ring_buffer *buffer);
 void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu);
 void ring_buffer_reset(struct ring_buffer *buffer);
 
+#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
 int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
 			 struct ring_buffer *buffer_b, int cpu);
+#else
+static inline int
+ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
+		     struct ring_buffer *buffer_b, int cpu)
+{
+	return -ENODEV;
+}
+#endif
 
 int ring_buffer_empty(struct ring_buffer *buffer);
 int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu);
diff --git a/trunk/kernel/trace/Kconfig b/trunk/kernel/trace/Kconfig
index 163fbfc2f39f..1ea0d1234f4a 100644
--- a/trunk/kernel/trace/Kconfig
+++ b/trunk/kernel/trace/Kconfig
@@ -62,6 +62,12 @@ config EVENT_TRACING
 config CONTEXT_SWITCH_TRACER
 	bool
 
+config RING_BUFFER_ALLOW_SWAP
+	bool
+	help
+	 Allow the use of ring_buffer_swap_cpu.
+	 Adds a very slight overhead to tracing when enabled.
+
 # All tracer options should select GENERIC_TRACER. For those options that are
 # enabled by all tracers (context switch and event tracer) they select TRACING.
 # This allows those options to appear when no other tracer is selected. But the
@@ -146,6 +152,7 @@ config IRQSOFF_TRACER
 	select TRACE_IRQFLAGS
 	select GENERIC_TRACER
 	select TRACER_MAX_TRACE
+	select RING_BUFFER_ALLOW_SWAP
 	help
 	  This option measures the time spent in irqs-off critical
 	  sections, with microsecond accuracy.
@@ -167,6 +174,7 @@ config PREEMPT_TRACER
 	depends on PREEMPT
 	select GENERIC_TRACER
 	select TRACER_MAX_TRACE
+	select RING_BUFFER_ALLOW_SWAP
 	help
 	  This option measures the time spent in preemption off critical
 	  sections, with microsecond accuracy.
diff --git a/trunk/kernel/trace/ring_buffer.c b/trunk/kernel/trace/ring_buffer.c
index 1766c0e8db5a..454e74e718cf 100644
--- a/trunk/kernel/trace/ring_buffer.c
+++ b/trunk/kernel/trace/ring_buffer.c
@@ -2084,6 +2084,7 @@ rb_reserve_next_event(struct ring_buffer *buffer,
 
 	rb_start_commit(cpu_buffer);
 
+#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
 	/*
 	 * Due to the ability to swap a cpu buffer from a buffer
 	 * it is possible it was swapped before we committed.
@@ -2096,6 +2097,7 @@ rb_reserve_next_event(struct ring_buffer *buffer,
 		local_dec(&cpu_buffer->commits);
 		return NULL;
 	}
+#endif
 
 	length = rb_calculate_event_length(length);
  again:
@@ -3498,6 +3500,7 @@ int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
 }
 EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
 
+#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
 /**
  * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
  * @buffer_a: One buffer to swap with
@@ -3573,6 +3576,7 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
 	return ret;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
+#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
 
 /**
  * ring_buffer_alloc_read_page - allocate a page to read from buffer