ocfs2: abstract out allocation locking

Right now, file allocation for ocfs2 is done within ocfs2_extend_file(),
which is either called from ->setattr() (for an i_size change), or at the
top of ocfs2_file_aio_write().

Inodes on file systems with sparse file support will want to do their
allocation during the actual write call.

In either case the cluster locking decisions are the same. We abstract out
that code into a new function, ocfs2_lock_allocators() which will be used by
a later patch to enable writing to sparse files.

This also provides a nice cleanup of ocfs2_extend_allocation().

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

fs/ocfs2/file.c

@@ -480,13 +480,86 @@ leave:
 	return status;
 }
 
+/*
+ * For a given allocation, determine which allocators will need to be
+ * accessed, and lock them, reserving the appropriate number of bits.
+ *
+ * Called from ocfs2_extend_allocation() for file systems which don't
+ * support holes, and from ocfs2_prepare_write() for file systems
+ * which understand sparse inodes.
+ */
+static int ocfs2_lock_allocators(struct inode *inode, struct ocfs2_dinode *di,
+				 u32 clusters_to_add,
+				 struct ocfs2_alloc_context **data_ac,
+				 struct ocfs2_alloc_context **meta_ac)
+{
+	int ret, num_free_extents;
+	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
+
+	*meta_ac = NULL;
+	*data_ac = NULL;
+
+	mlog(0, "extend inode %llu, i_size = %lld, di->i_clusters = %u, "
+	     "clusters_to_add = %u\n",
+	     (unsigned long long)OCFS2_I(inode)->ip_blkno, i_size_read(inode),
+	     le32_to_cpu(di->i_clusters), clusters_to_add);
+
+	num_free_extents = ocfs2_num_free_extents(osb, inode, di);
+	if (num_free_extents < 0) {
+		ret = num_free_extents;
+		mlog_errno(ret);
+		goto out;
+	}
+
+	/*
+	 * Sparse allocation file systems need to be more conservative
+	 * with reserving room for expansion - the actual allocation
+	 * happens while we've got a journal handle open so re-taking
+	 * a cluster lock (because we ran out of room for another
+	 * extent) will violate ordering rules.
+	 *
+	 * Most of the time we'll only be seeing this 1 page at a time
+	 * anyway.
+	 */
+	if (!num_free_extents ||
+	    (ocfs2_sparse_alloc(osb) && num_free_extents < clusters_to_add)) {
+		ret = ocfs2_reserve_new_metadata(osb, di, meta_ac);
+		if (ret < 0) {
+			if (ret != -ENOSPC)
+				mlog_errno(ret);
+			goto out;
+		}
+	}
+
+	ret = ocfs2_reserve_clusters(osb, clusters_to_add, data_ac);
+	if (ret < 0) {
+		if (ret != -ENOSPC)
+			mlog_errno(ret);
+		goto out;
+	}
+
+out:
+	if (ret) {
+		if (*meta_ac) {
+			ocfs2_free_alloc_context(*meta_ac);
+			*meta_ac = NULL;
+		}
+
+		/*
+		 * We cannot have an error and a non null *data_ac.
+		 */
+	}
+
+	return ret;
+}
+
 static int ocfs2_extend_allocation(struct inode *inode,
 				   u32 clusters_to_add)
 {
 	int status = 0;
 	int restart_func = 0;
 	int drop_alloc_sem = 0;
-	int credits, num_free_extents;
+	int credits;
 	u32 prev_clusters, logical_start;
 	struct buffer_head *bh = NULL;
 	struct ocfs2_dinode *fe = NULL;
@@ -523,36 +596,13 @@ static int ocfs2_extend_allocation(struct inode *inode,
 restart_all:
 	BUG_ON(le32_to_cpu(fe->i_clusters) != OCFS2_I(inode)->ip_clusters);
 
-	mlog(0, "extend inode %llu, i_size = %lld, fe->i_clusters = %u, "
-	     "clusters_to_add = %u\n",
-	     (unsigned long long)OCFS2_I(inode)->ip_blkno, i_size_read(inode),
-	     fe->i_clusters, clusters_to_add);
-
-	num_free_extents = ocfs2_num_free_extents(osb,
-						  inode,
-						  fe);
-	if (num_free_extents < 0) {
-		status = num_free_extents;
+	status = ocfs2_lock_allocators(inode, fe, clusters_to_add, &data_ac,
+				       &meta_ac);
+	if (status) {
 		mlog_errno(status);
 		goto leave;
 	}
 
-	if (!num_free_extents) {
-		status = ocfs2_reserve_new_metadata(osb, fe, &meta_ac);
-		if (status < 0) {
-			if (status != -ENOSPC)
-				mlog_errno(status);
-			goto leave;
-		}
-	}
-
-	status = ocfs2_reserve_clusters(osb, clusters_to_add, &data_ac);
-	if (status < 0) {
-		if (status != -ENOSPC)
-			mlog_errno(status);
-		goto leave;
-	}
-
 	/* blocks peope in read/write from reading our allocation
 	 * until we're done changing it. We depend on i_mutex to block
 	 * other extend/truncate calls while we're here. Ordering wrt