--- linux-2.6.9-22.EL/include/linux/fs.h	2005-12-07 12:43:55.000000000 -0500
+++ linux.truncate/include/linux/fs.h	2005-12-02 00:25:22.000000000 -0500
@@ -1509,7 +1509,8 @@ ssize_t __blockdev_direct_IO(int rw, str
 	int lock_type);
 
 enum {
-	DIO_LOCKING = 1, /* need locking between buffered and direct access */
+	DIO_CLUSTER_LOCKING = 0, /* allow (cluster) fs handle its own locking */
+	DIO_LOCKING,     /* need locking between buffered and direct access */
 	DIO_NO_LOCKING,  /* bdev; no locking at all between buffered/direct */
 	DIO_OWN_LOCKING, /* filesystem locks buffered and direct internally */
 };
@@ -1541,6 +1542,15 @@ static inline ssize_t blockdev_direct_IO
 				nr_segs, get_blocks, end_io, DIO_OWN_LOCKING);
 }
 
+static inline ssize_t blockdev_direct_IO_cluster_locking(int rw, struct kiocb *iocb,
+	struct inode *inode, struct block_device *bdev, const struct iovec *iov,
+	loff_t offset, unsigned long nr_segs, get_blocks_t get_blocks,
+	dio_iodone_t end_io)
+{
+	return __blockdev_direct_IO(rw, iocb, inode, bdev, iov, offset,
+			nr_segs, get_blocks, end_io, DIO_CLUSTER_LOCKING);
+}
+
 extern struct file_operations generic_ro_fops;
 
 #define special_file(m) (S_ISCHR(m)||S_ISBLK(m)||S_ISFIFO(m)||S_ISSOCK(m))
--- linux-2.6.9-22.EL/fs/direct-io.c	2005-11-09 17:26:02.000000000 -0500
+++ linux.truncate/fs/direct-io.c	2005-12-07 12:27:17.000000000 -0500
@@ -515,7 +515,7 @@ static int get_more_blocks(struct dio *d
 			fs_count++;
 
 		create = dio->rw == WRITE;
-		if (dio->lock_type == DIO_LOCKING) {
+		if ((dio->lock_type == DIO_LOCKING) || (dio->lock_type == DIO_CLUSTER_LOCKING)) {
 			if (dio->block_in_file < (i_size_read(dio->inode) >>
 							dio->blkbits))
 				create = 0;
@@ -1183,9 +1183,16 @@ __blockdev_direct_IO(int rw, struct kioc
 	 * For regular files using DIO_OWN_LOCKING,
 	 *	neither readers nor writers take any locks here
 	 *	(i_sem is already held and release for writers here)
+	 * The DIO_CLUSTER_LOCKING allows (cluster) filesystem manages its own
+	 *	locking (bypassing i_sem and i_alloc_sem handling within
+	 *	__blockdev_direct_IO()).
 	 */
+
 	dio->lock_type = dio_lock_type;
-	if (dio_lock_type != DIO_NO_LOCKING) {
+	if (dio_lock_type == DIO_CLUSTER_LOCKING)
+		goto cluster_skip_locking;
+
+	if (dio_lock_type != DIO_NO_LOCKING) { 
 		if (rw == READ) {
 			struct address_space *mapping;
 
@@ -1205,6 +1212,9 @@ __blockdev_direct_IO(int rw, struct kioc
 		if (dio_lock_type == DIO_LOCKING)
 			down_read(&inode->i_alloc_sem);
 	}
+
+cluster_skip_locking:
+
 	/*
 	 * For file extending writes updating i_size before data
 	 * writeouts complete can expose uninitialized blocks. So