[PATCH 2/3] ocfs2: add ocfs2_overwrite_io function

[Gang He]

Add ocfs2_overwrite_io function, which is used to judge if
overwrite allocated blocks, otherwise, the write will bring extra
block allocation overhead.

Signed-off-by: Gang He <ghe@xxxxxxxx>
---
 fs/ocfs2/extent_map.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/ocfs2/extent_map.h |  3 +++
 2 files changed, 70 insertions(+)

diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
index e4719e0..98bf325 100644
--- a/fs/ocfs2/extent_map.c
+++ b/fs/ocfs2/extent_map.c
@@ -832,6 +832,73 @@ int ocfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 	return ret;
 }
 
+/* Is IO overwriting allocated blocks? */
+int ocfs2_overwrite_io(struct inode *inode, u64 map_start, u64 map_len,
+		       int wait)
+{
+	int ret = 0, is_last;
+	u32 mapping_end, cpos;
+	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
+	struct buffer_head *di_bh = NULL;
+	struct ocfs2_extent_rec rec;
+
+	if (wait)
+		ret = ocfs2_inode_lock(inode, &di_bh, 0);
+	else
+		ret = ocfs2_try_inode_lock(inode, &di_bh, 0);
+	if (ret)
+		goto out;
+
+	if (wait)
+		down_read(&OCFS2_I(inode)->ip_alloc_sem);
+	else {
+		if (!down_read_trylock(&OCFS2_I(inode)->ip_alloc_sem)) {
+			ret = -EAGAIN;
+			goto out_unlock1;
+		}
+	}
+
+	if ((OCFS2_I(inode)->ip_dyn_features & OCFS2_INLINE_DATA_FL) &&
+	   ((map_start + map_len) <= i_size_read(inode)))
+		goto out_unlock2;
+
+	cpos = map_start >> osb->s_clustersize_bits;
+	mapping_end = ocfs2_clusters_for_bytes(inode->i_sb,
+					       map_start + map_len);
+	is_last = 0;
+	while (cpos < mapping_end && !is_last) {
+		ret = ocfs2_get_clusters_nocache(inode, di_bh, cpos,
+						 NULL, &rec, &is_last);
+		if (ret) {
+			mlog_errno(ret);
+			goto out_unlock2;
+		}
+
+		if (rec.e_blkno == 0ULL)
+			break;
+
+		if (rec.e_flags & OCFS2_EXT_REFCOUNTED)
+			break;
+
+		cpos = le32_to_cpu(rec.e_cpos) +
+			le16_to_cpu(rec.e_leaf_clusters);
+	}
+
+	if (cpos < mapping_end)
+		ret = 1;
+
+out_unlock2:
+	brelse(di_bh);
+
+	up_read(&OCFS2_I(inode)->ip_alloc_sem);
+
+out_unlock1:
+	ocfs2_inode_unlock(inode, 0);
+
+out:
+	return (ret ? 0 : 1);
+}
+
 int ocfs2_seek_data_hole_offset(struct file *file, loff_t *offset, int whence)
 {
 	struct inode *inode = file->f_mapping->host;
diff --git a/fs/ocfs2/extent_map.h b/fs/ocfs2/extent_map.h
index 67ea57d..fd9e86a 100644
--- a/fs/ocfs2/extent_map.h
+++ b/fs/ocfs2/extent_map.h
@@ -53,6 +53,9 @@ int ocfs2_extent_map_get_blocks(struct inode *inode, u64 v_blkno, u64 *p_blkno,
 int ocfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		 u64 map_start, u64 map_len);
 
+int ocfs2_overwrite_io(struct inode *inode, u64 map_start, u64 map_len,
+		       int wait);
+
 int ocfs2_seek_data_hole_offset(struct file *file, loff_t *offset, int origin);
 
 int ocfs2_xattr_get_clusters(struct inode *inode, u32 v_cluster,
-- 
1.8.5.6