3 files changed, 23 insertions, 6 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index bd1c35a4fbcc..269db80a961e 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1429,6 +1429,17 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
 }
 EXPORT_SYMBOL_GPL(ring_buffer_resize);
 
+void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val)
+{
+        mutex_lock(&buffer->mutex);
+        if (val)
+                buffer->flags |= RB_FL_OVERWRITE;
+        else
+                buffer->flags &= ~RB_FL_OVERWRITE;
+        mutex_unlock(&buffer->mutex);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
+
 static inline void *
 __rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
 {
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8dc8da6733f9..85e3ee1e474e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -41,8 +41,6 @@
 #include "trace.h"
 #include "trace_output.h"
 
-#define TRACE_BUFFER_FLAGS      (RB_FL_OVERWRITE)
-
 /*
  * On boot up, the ring buffer is set to the minimum size, so that
  * we do not waste memory on systems that are not using tracing.
@@ -340,7 +338,7 @@ static DECLARE_WAIT_QUEUE_HEAD(trace_wait);
 /* trace_flags holds trace_options default values */
 unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK |
         TRACE_ITER_ANNOTATE | TRACE_ITER_CONTEXT_INFO | TRACE_ITER_SLEEP_TIME |
-        TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD;
+        TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD | TRACE_ITER_OVERWRITE;
 
 static int trace_stop_count;
 static DEFINE_SPINLOCK(tracing_start_lock);
@@ -425,6 +423,7 @@ static const char *trace_options[] = {
         "sleep-time",
         "graph-time",
         "record-cmd",
+        "overwrite",
         NULL
 };
 
@@ -2529,6 +2528,9 @@ static void set_tracer_flags(unsigned int mask, int enabled)
 
         if (mask == TRACE_ITER_RECORD_CMD)
                 trace_event_enable_cmd_record(enabled);
+
+        if (mask == TRACE_ITER_OVERWRITE)
+                ring_buffer_change_overwrite(global_trace.buffer, enabled);
 }
 
 static ssize_t
@@ -4555,9 +4557,11 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
 __init static int tracer_alloc_buffers(void)
 {
         int ring_buf_size;
+        enum ring_buffer_flags rb_flags;
         int i;
         int ret = -ENOMEM;
 
+
         if (!alloc_cpumask_var(&tracing_buffer_mask, GFP_KERNEL))
                 goto out;
 
@@ -4570,12 +4574,13 @@ __init static int tracer_alloc_buffers(void)
         else
                 ring_buf_size = 1;
 
+        rb_flags = trace_flags & TRACE_ITER_OVERWRITE ? RB_FL_OVERWRITE : 0;
+
         cpumask_copy(tracing_buffer_mask, cpu_possible_mask);
         cpumask_copy(tracing_cpumask, cpu_all_mask);
 
         /* TODO: make the number of buffers hot pluggable with CPUS */
-        global_trace.buffer = ring_buffer_alloc(ring_buf_size,
-                                                   TRACE_BUFFER_FLAGS);
+        global_trace.buffer = ring_buffer_alloc(ring_buf_size, rb_flags);
         if (!global_trace.buffer) {
                 printk(KERN_ERR "tracer: failed to allocate ring buffer!\n");
                 WARN_ON(1);
@@ -4585,7 +4590,7 @@ __init static int tracer_alloc_buffers(void)
 
 
 #ifdef CONFIG_TRACER_MAX_TRACE
-        max_tr.buffer = ring_buffer_alloc(1, TRACE_BUFFER_FLAGS);
+        max_tr.buffer = ring_buffer_alloc(1, rb_flags);
         if (!max_tr.buffer) {
                 printk(KERN_ERR "tracer: failed to allocate max ring buffer!\n");
                 WARN_ON(1);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 856e73cc1d3f..951d0b7e7062 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -606,6 +606,7 @@ enum trace_iterator_flags {
         TRACE_ITER_SLEEP_TIME           = 0x40000,
         TRACE_ITER_GRAPH_TIME           = 0x80000,
         TRACE_ITER_RECORD_CMD           = 0x100000,
+        TRACE_ITER_OVERWRITE            = 0x200000,
 };
 
 /*