[PATCH 2/6 v3][RFC] Btrfs: add helper function to test if we can merge state

[Liu Bo <liubo2009@cn.fujitsu.com>]

This is a helper function to test if two states are adjacent.

It is used for applying rwlock for extent state.

Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
---
 fs/btrfs/extent_io.c |   27 +++++++++++++++++++++++++++
 1 files changed, 27 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 1858d86..4c6dd85 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -473,6 +473,33 @@ void extent_io_tree_panic(struct extent_io_tree *tree, int err)
 		    "thread while locked.");
 }
 
+static int test_merge_state(struct extent_io_tree *tree,
+			    struct extent_state *state)
+{
+	struct extent_state *other;
+	struct rb_node *other_node;
+
+	if (state->state & (EXTENT_IOBITS | EXTENT_BOUNDARY))
+		return 0;
+
+	other_node = rb_prev(&state->rb_node);
+	if (other_node) {
+		other = rb_entry(other_node, struct extent_state, rb_node);
+		if (other->end == state->start - 1 &&
+		    other->state == state->state)
+			return 1;
+	}
+	other_node = rb_next(&state->rb_node);
+	if (other_node) {
+		other = rb_entry(other_node, struct extent_state, rb_node);
+		if (other->start == state->end + 1 &&
+		    other->state == state->state)
+			return 1;
+	}
+
+	return 0;
+}
+
 /*
  * clear some bits on a range in the tree.  This may require splitting
  * or inserting elements in the tree, so the gfp mask is used to
-- 
1.6.5.2