[PATCH] trace-cmd: add trace_hash_find_reverse

[Josef Bacik <jbacik@fb.com>]

Sometimes we want to FIFO identical entries in the hash table, so add
trace_hash_find_reverse, which will cycle through the hash list in reverse.
This is helpful in our case where we are monitoring block request issues to
match with their corresponding completes, if we issue multiple times to the same
block we want to be able to match them with the correct completes (more or less
anyway).  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
---
 list.h       |  5 +++++
 trace-hash.c | 22 ++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/list.h b/list.h
index 9817871..93c64f5 100644
--- a/list.h
+++ b/list.h
@@ -79,4 +79,9 @@ static inline int list_empty(struct list_head *list)
 	     &(p)->field != list;					\
 	     p = n, n = container_of((p)->field.next, typeof(*p), field))
 
+#define list_for_each_entry_reverse(p, list, field)			\
+	for (p = container_of((list)->prev, typeof(*p), field);		\
+	     &p->field != list;						\
+	     p = container_of((p)->field.prev, typeof(*p), field))
+
 #endif /* __LIST_H */
diff --git a/trace-hash.c b/trace-hash.c
index 5ffe61c..0dc4f73 100644
--- a/trace-hash.c
+++ b/trace-hash.c
@@ -94,3 +94,25 @@ trace_hash_find(struct trace_hash *hash, unsigned long long key,
 
 	return NULL;
 }
+
+struct trace_hash_item *
+trace_hash_find_reverse(struct trace_hash *hash, unsigned long long key,
+			trace_hash_func match, void *data)
+{
+	struct trace_hash_item *item;
+	struct list_head *bucket;
+	int bucket_nr = hash->power ? key & hash->power :
+		key % hash->nr_buckets;
+
+	bucket = hash->buckets + bucket_nr;
+	list_for_each_entry_reverse(item, bucket, list) {
+		if (item->key == key) {
+			if (!match)
+				return item;
+			if (match(item, data))
+				return item;
+		}
+	}
+
+	return NULL;
+}
-- 
2.5.0