ocfs2: teach extend/truncate about sparse files

For ocfs2_truncate_file(), we eliminate the "simple" truncate case which no
longer exists since i_size is not tied to i_clusters. In
ocfs2_extend_file(), we skip the allocation / page zeroing code for file
systems which understand sparse files.

The core truncate code is changed to do a bottom up tree traversal. This
gets abstracted out into it's own function. To make things more readable,
most of the special case handling for in-inode extents from
ocfs2_do_truncate() is also removed.

Though write support for sparse files comes in a later patch, we at least
update ocfs2_prepare_inode_for_write() to skip allocation for sparse files.
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

fs/ocfs2/file.c

@@ -344,18 +344,6 @@ static int ocfs2_truncate_file(struct inode *inode,
 	}
 	ocfs2_data_unlock(inode, 1);
 
-	if (le32_to_cpu(fe->i_clusters) ==
-	    ocfs2_clusters_for_bytes(osb->sb, new_i_size)) {
-		mlog(0, "fe->i_clusters = %u, so we do a simple truncate\n",
-		     fe->i_clusters);
-		/* No allocation change is required, so lets fast path
-		 * this truncate. */
-		status = ocfs2_simple_size_update(inode, di_bh, new_i_size);
-		if (status < 0)
-			mlog_errno(status);
-		goto bail;
-	}
-
 	/* alright, we're going to need to do a full blown alloc size
 	 * change. Orphan the inode so that recovery can complete the
 	 * truncate if necessary. This does the task of marking
@@ -785,7 +773,7 @@ static int ocfs2_extend_file(struct inode *inode,
 			     size_t tail_to_skip)
 {
 	int ret = 0;
-	u32 clusters_to_add;
+	u32 clusters_to_add = 0;
 
 	BUG_ON(!tail_to_skip && !di_bh);
 
@@ -797,6 +785,11 @@ static int ocfs2_extend_file(struct inode *inode,
   		goto out;
 	BUG_ON(new_i_size < i_size_read(inode));
 
+	if (ocfs2_sparse_alloc(OCFS2_SB(inode->i_sb))) {
+		BUG_ON(tail_to_skip != 0);
+		goto out_update_size;
+	}
+
 	clusters_to_add = ocfs2_clusters_for_bytes(inode->i_sb, new_i_size) - 
 		OCFS2_I(inode)->ip_clusters;
 
@@ -832,6 +825,7 @@ static int ocfs2_extend_file(struct inode *inode,
 		goto out_unlock;
 	}
 
+out_update_size:
 	if (!tail_to_skip) {
 		/* We're being called from ocfs2_setattr() which wants
 		 * us to update i_size */
@@ -841,6 +835,7 @@ static int ocfs2_extend_file(struct inode *inode,
 	}
 
 out_unlock:
+	if (!ocfs2_sparse_alloc(OCFS2_SB(inode->i_sb)))
 		ocfs2_data_unlock(inode, 1);
 
 out:
@@ -1097,6 +1092,14 @@ static int ocfs2_prepare_inode_for_write(struct dentry *dentry,
 		} else {
 			saved_pos = *ppos;
 		}
+
+		/*
+		 * The rest of this loop is concerned with legacy file
+		 * systems which don't support sparse files.
+		 */
+		if (ocfs2_sparse_alloc(OCFS2_SB(inode->i_sb)))
+			break;
+
 		newsize = count + saved_pos;
 
 		mlog(0, "pos=%lld newsize=%lld cursize=%lld\n",

fs/ocfs2/inode.c

@@ -487,7 +487,6 @@ static int ocfs2_truncate_for_delete(struct ocfs2_super *osb,
 				     struct buffer_head *fe_bh)
 {
 	int status = 0;
-	handle_t *handle = NULL;
 	struct ocfs2_truncate_context *tc = NULL;
 	struct ocfs2_dinode *fe;
 
@@ -495,41 +494,20 @@ static int ocfs2_truncate_for_delete(struct ocfs2_super *osb,
 
 	fe = (struct ocfs2_dinode *) fe_bh->b_data;
 
-	/* zero allocation, zero truncate :) */
-	if (!fe->i_clusters)
-		goto bail;
-
-	handle = ocfs2_start_trans(osb, OCFS2_INODE_UPDATE_CREDITS);
-	if (IS_ERR(handle)) {
-		status = PTR_ERR(handle);
-		handle = NULL;
-		mlog_errno(status);
-		goto bail;
-	}
-
-	status = ocfs2_set_inode_size(handle, inode, fe_bh, 0ULL);
-	if (status < 0) {
-		mlog_errno(status);
-		goto bail;
-	}
-
-	ocfs2_commit_trans(osb, handle);
-	handle = NULL;
-
+	if (fe->i_clusters) {
 		status = ocfs2_prepare_truncate(osb, inode, fe_bh, &tc);
 		if (status < 0) {
 			mlog_errno(status);
-		goto bail;
+			goto out;
 		}
 
 		status = ocfs2_commit_truncate(osb, inode, fe_bh, tc);
 		if (status < 0) {
 			mlog_errno(status);
-		goto bail;
+			goto out;
 		}
-bail:
-	if (handle)
-		ocfs2_commit_trans(osb, handle);
+	}
+out:
 
 	mlog_exit(status);
 	return status;