[PATCH v5 4/6] Btrfs: heuristic add detection of zeroed sample

[Timofey Titovets <nefelim4ag@gmail.com>]

Use memcmp for check sample data to zeroes.

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
---
 fs/btrfs/heuristic.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/fs/btrfs/heuristic.c b/fs/btrfs/heuristic.c
index 5336638a3b7c..4557ea1db373 100644
--- a/fs/btrfs/heuristic.c
+++ b/fs/btrfs/heuristic.c
@@ -73,6 +73,21 @@ static struct list_head *heuristic_alloc_workspace(void)
 	return ERR_PTR(-ENOMEM);
 }

+static bool sample_zeroed(struct workspace *workspace)
+{
+	u32 i;
+	u8 zero[READ_SIZE];
+
+	memset(&zero, 0, sizeof(zero));
+
+	for (i = 0; i < workspace->sample_size; i += sizeof(zero)) {
+		if (memcmp(&workspace->sample[i], &zero, sizeof(zero)))
+			return false;
+	}
+
+	return true;
+}
+
 static int heuristic(struct list_head *ws, struct inode *inode,
 		     u64 start, u64 end)
 {
@@ -110,6 +125,9 @@ static int heuristic(struct list_head *ws, struct inode *inode,

 	workspace->sample_size = b;

+	if (sample_zeroed(workspace))
+		return 1;
+
 	memset(workspace->bucket, 0, sizeof(*workspace->bucket)*BUCKET_SIZE);

 	for (a = 0; a < workspace->sample_size; a++) {
--
2.14.1