[sheepdog] [PATCH 1/4] trace: fix negative index for ret stack array

[Liu Yuan]

From: Liu Yuan <tailai.ly at taobao.com>

In some unusual corner cases, pop_return_trace() will be called first, to
avoid negative index, we start at the middle of array. On the buffer reader
side, we can minus TRACE_RET_STACK_LEN / 2 to identify those negative index
which are actually uselss because we don't store their entry time.

Signed-off-by: Liu Yuan <tailai.ly at taobao.com>
---
 collie/debug.c      |  8 +++++++-
 include/sheep.h     |  2 ++
 sheep/trace/graph.c | 11 +++++++++--
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/collie/debug.c b/collie/debug.c
index 250a131..c40d164 100644
--- a/collie/debug.c
+++ b/collie/debug.c
@@ -53,6 +53,11 @@ static inline void print_finale(struct trace_graph_item *item)
 
 static void print_trace_item(struct trace_graph_item *item)
 {
+	item->depth -= TRACE_RET_STACK_LEN / 2;
+	/* Ignore the item that doesn't have entry time stored */
+	if (item->depth < 0)
+		return;
+
 	print_thread_name(item);
 	print_time(item);
 	print_finale(item);
@@ -180,7 +185,8 @@ static int trace_cat(int argc, char **argv)
 		return EXIT_SYSFAIL;
 	}
 
-	map = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	map = mmap(NULL, st.st_size, PROT_READ | PROT_WRITE,
+		   MAP_PRIVATE, fd, 0);
 	close(fd);
 	if (map == MAP_FAILED) {
 		fprintf(stderr, "%m\n");
diff --git a/include/sheep.h b/include/sheep.h
index a2d0cd9..36de58b 100644
--- a/include/sheep.h
+++ b/include/sheep.h
@@ -47,6 +47,8 @@ struct vdi_copy {
 #define TRACE_FNAME_LEN    36
 #define TRACE_THREAD_LEN   20
 
+#define TRACE_RET_STACK_LEN 100
+
 struct trace_graph_item {
 	char tname[TRACE_THREAD_LEN];
 	int type;
diff --git a/sheep/trace/graph.c b/sheep/trace/graph.c
index ab3a6c3..e39b801 100644
--- a/sheep/trace/graph.c
+++ b/sheep/trace/graph.c
@@ -19,12 +19,19 @@
 #include "logger.h"
 #include "util.h"
 
-static __thread int ret_stack_index;
+/*
+ * In some unusual corner cases, pop_return_trace() will be called first, to
+ * avoid negative index, we start at the middle of array. On the buffer reader
+ * side, we can minus TRACE_RET_STACK_LEN / 2 to identify those negative index
+ * which are actually uselss because we don't store their entry time.
+ */
+static __thread int ret_stack_index = TRACE_RET_STACK_LEN / 2;
+
 static __thread struct trace_ret_stack {
 	unsigned long ret;
 	unsigned long func;
 	unsigned long long entry_time;
-} trace_ret_stack[100]; /* FIXME: consider stack overrun */
+} trace_ret_stack[TRACE_RET_STACK_LEN]; /* FIXME: consider stack overrun */
 
 static void push_return_trace(unsigned long ret, unsigned long long etime,
 		unsigned long func, int *depth)
-- 
1.7.12.84.gefa6462