tracing: Add an 'overwrite' trace_option.

Add an "overwrite" trace_option for ftrace to control whether the buffer should
be overwritten on overflow or not. The default remains to overwrite old events
when the buffer is full. This patch adds the option to instead discard newest
events when the buffer is full. This is useful to get a snapshot of traces just
after enabling traces. Dropping the current event is also a simpler code path.

Signed-off-by: David Sharp <dhsharp@google.com>
LKML-Reference: <1291844807-15481-1-git-send-email-dhsharp@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
index 67f1cc473257b6e646dcd27a3d9b7800096ecacd..1ebc24cf9a55af0bf1b9607d1b452e2f828ab601 100644 (file)
--- a/Documentation/trace/ftrace.txt
+++ b/Documentation/trace/ftrace.txt
@@ -454,6 +454,11 @@ x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
                    latencies, as described in "Latency
                    trace format".
 
+  overwrite - This controls what happens when the trace buffer is
+              full. If "1" (default), the oldest events are
+              discarded and overwritten. If "0", then the newest
+              events are discarded.
+
 ftrace_enabled
 --------------
 

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 8d3a2486544d1d91583e703b45d9b90794d2cca1..ab38ac80b0f9c7c4979a30475626c9bf2fbffa36 100644 (file)
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -100,6 +100,8 @@ void ring_buffer_free(struct ring_buffer *buffer);
 
 int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size);
 
+void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val);
+
 struct ring_buffer_event *ring_buffer_lock_reserve(struct ring_buffer *buffer,
                                                   unsigned long length);
 int ring_buffer_unlock_commit(struct ring_buffer *buffer,

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index bd1c35a4fbccf31c0531f0667545011f704c561f..269db80a961e8b8fb01b27b52ae4072829b7d2d5 100644 (file)
--- 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 8dc8da6733f97994f79dca7a88ab4a7c4cc4a3f7..85e3ee1e474e1a1336507dd592c1ab9f8619344f 100644 (file)
--- 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 856e73cc1d3f7010b67eff60b356cf075d1f8c2f..951d0b7e7062e6b67da9abe7c24e9d8c036d3e2a 100644 (file)
--- 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,
 };
 
 /*