[PATCH v4 10/13] tracing/ring-buffer: Add last_boot_info file to boot instance

[Steven Rostedt <rostedt@goodmis.org>]

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

If an instance is mapped to memory on boot up, create a new file called
"last_boot_info" that will hold information that can be used to properly
parse the raw data in the ring buffer.

It will export the delta of the addresses for text and data from what it
was from the last boot. It does not expose actually addresses (unless you
knew what the actual address was from the last boot).

The output will look like:

 # cat last_boot_info
 text delta:	-268435456
 data delta:	-268435456

The text and data are kept separate in case they are ever made different.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/ring_buffer.h |  3 +++
 kernel/trace/ring_buffer.c  | 23 ++++++++++++++++++
 kernel/trace/trace.c        | 47 ++++++++++++++++++++++++++++++++++++-
 kernel/trace/trace.h        |  2 ++
 4 files changed, 74 insertions(+), 1 deletion(-)

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index a50b0223b1d3..55de3798a9b9 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -94,6 +94,9 @@ struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flag
 					       unsigned long range_size,
 					       struct lock_class_key *key);
 
+bool ring_buffer_last_boot_delta(struct trace_buffer *buffer, long *text,
+				 long *data);
+
 /*
  * Because the ring buffer is generic, if other users of the ring buffer get
  * traced by ftrace, it can produce lockdep warnings. We need to keep each
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index ab6b8a0ee8e1..8c1d7ea01e6f 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2394,6 +2394,29 @@ struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flag
 	return alloc_buffer(size, flags, order, start, start + range_size, key);
 }
 
+/**
+ * ring_buffer_last_boot_delta - return the delta offset from last boot
+ * @buffer: The buffer to return the delta from
+ * @text: Return text delta
+ * @data: Return data delta
+ *
+ * Returns: The true if the delta is non zero
+ */
+bool ring_buffer_last_boot_delta(struct trace_buffer *buffer, long *text,
+				 long *data)
+{
+	if (!buffer)
+		return false;
+
+	if (!buffer->last_text_delta)
+		return false;
+
+	*text = buffer->last_text_delta;
+	*data = buffer->last_data_delta;
+
+	return true;
+}
+
 /**
  * ring_buffer_free - free a ring buffer.
  * @buffer: the buffer to free.
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index dfde26aa3211..dc4eee33d920 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6041,6 +6041,18 @@ ssize_t tracing_resize_ring_buffer(struct trace_array *tr,
 	return ret;
 }
 
+static void update_last_data(struct trace_array *tr)
+{
+	if (!tr->text_delta && !tr->data_delta)
+		return;
+
+	/* Clear old data */
+	tracing_reset_online_cpus(&tr->array_buffer);
+
+	/* Using current data now */
+	tr->text_delta = 0;
+	tr->data_delta = 0;
+}
 
 /**
  * tracing_update_buffers - used by tracing facility to expand ring buffers
@@ -6058,6 +6070,9 @@ int tracing_update_buffers(struct trace_array *tr)
 	int ret = 0;
 
 	mutex_lock(&trace_types_lock);
+
+	update_last_data(tr);
+
 	if (!tr->ring_buffer_expanded)
 		ret = __tracing_resize_ring_buffer(tr, trace_buf_size,
 						RING_BUFFER_ALL_CPUS);
@@ -6113,6 +6128,8 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
 
 	mutex_lock(&trace_types_lock);
 
+	update_last_data(tr);
+
 	if (!tr->ring_buffer_expanded) {
 		ret = __tracing_resize_ring_buffer(tr, trace_buf_size,
 						RING_BUFFER_ALL_CPUS);
@@ -6860,6 +6877,21 @@ tracing_total_entries_read(struct file *filp, char __user *ubuf,
 	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
 }
 
+static ssize_t
+tracing_last_boot_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
+{
+	struct trace_array *tr = filp->private_data;
+	struct seq_buf seq;
+	char buf[64];
+
+	seq_buf_init(&seq, buf, 64);
+
+	seq_buf_printf(&seq, "text delta:\t%ld\n", tr->text_delta);
+	seq_buf_printf(&seq, "data delta:\t%ld\n", tr->data_delta);
+
+	return simple_read_from_buffer(ubuf, cnt, ppos, buf, seq_buf_used(&seq));
+}
+
 static int tracing_buffer_meta_open(struct inode *inode, struct file *filp)
 {
 	struct trace_array *tr = inode->i_private;
@@ -7499,6 +7531,13 @@ static const struct file_operations trace_time_stamp_mode_fops = {
 	.release	= tracing_single_release_tr,
 };
 
+static const struct file_operations last_boot_fops = {
+	.open		= tracing_open_generic_tr,
+	.read		= tracing_last_boot_read,
+	.llseek		= generic_file_llseek,
+	.release	= tracing_release_generic_tr,
+};
+
 #ifdef CONFIG_TRACER_SNAPSHOT
 static const struct file_operations snapshot_fops = {
 	.open		= tracing_snapshot_open,
@@ -9242,6 +9281,9 @@ allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int size
 		buf->buffer = ring_buffer_alloc_range(size, rb_flags, 0,
 						      tr->range_addr_start,
 						      tr->range_addr_size);
+
+		ring_buffer_last_boot_delta(buf->buffer,
+					    &tr->text_delta, &tr->data_delta);
 		/*
 		 * This is basically the same as a mapped buffer,
 		 * with the same restrictions.
@@ -9751,7 +9793,10 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
 		MEM_FAIL(1, "Could not allocate function filter files");
 
 #ifdef CONFIG_TRACER_SNAPSHOT
-	if (!tr->range_addr_start) {
+	if (tr->range_addr_start) {
+		trace_create_file("last_boot_info", TRACE_MODE_READ, d_tracer,
+				  tr, &last_boot_fops);
+	} else {
 		trace_create_file("snapshot", TRACE_MODE_WRITE, d_tracer,
 				  tr, &snapshot_fops);
 	}
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 2efa4cccdd3b..611be17fdc70 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -347,6 +347,8 @@ struct trace_array {
 	/* The below is for memory mapped ring buffer */
 	unsigned long		range_addr_start;
 	unsigned long		range_addr_size;
+	long			text_delta;
+	long			data_delta;
 
 	struct trace_pid_list	__rcu *filtered_pids;
 	struct trace_pid_list	__rcu *filtered_no_pids;
-- 
2.43.0