---
 fs/ext4/ext4.h  |    3 ++
 fs/ext4/inode.c |   68 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+)

--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1838,6 +1838,9 @@ extern int ext4_page_mkwrite(struct vm_a
 extern qsize_t *ext4_get_reserved_space(struct inode *inode);
 extern void ext4_da_update_reserve_space(struct inode *inode,
 					int used, int quota_claim);
+extern int ext4_map_inode_page(struct inode *inode, struct page *page,
+			       unsigned long *blocks, int created);
+
 /* ioctl.c */
 extern long ext4_ioctl(struct file *, unsigned int, unsigned long);
 extern long ext4_compat_ioctl(struct file *, unsigned int, unsigned long);
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5968,3 +5968,65 @@ out_unlock:
 	up_read(&inode->i_alloc_sem);
 	return ret;
 }
+
+int ext4_map_inode_page(struct inode *inode, struct page *page,
+			unsigned long *blocks, int create)
+{
+	unsigned int blocksize, blocks_per_page;
+	unsigned long iblock;
+	struct ext4_map_blocks map;
+	void *handle;
+	int i, rc = 0, failed = 0, needed_blocks;
+
+	blocksize = inode->i_sb->s_blocksize;
+	blocks_per_page = PAGE_SIZE >> inode->i_sb->s_blocksize_bits;
+	iblock = page->index * blocks_per_page;
+
+	for (i = 0; i < blocks_per_page; i++, iblock++) {
+		blocks[i] = ext4_bmap(inode->i_mapping, iblock);
+		if (blocks[i] == 0) {
+			failed++;
+		}
+	}
+
+	if (failed == 0 || create == 0)
+		return 0;
+
+	needed_blocks = ext4_writepage_trans_blocks(inode);
+	handle = ext4_journal_start(inode, needed_blocks);
+	if (IS_ERR(handle))
+		return PTR_ERR(handle);
+
+	iblock = page->index * blocks_per_page;
+	for (i = 0; i < blocks_per_page; i++, iblock++) {
+		if (blocks[i] != 0)
+			continue;
+
+		map.m_lblk = iblock;
+		map.m_len = 1;
+		map.m_flags = 0;
+		rc = ext4_ind_map_blocks(handle, inode, &map,
+					 EXT4_GET_BLOCKS_CREATE);
+		if (rc < 0) {
+			printk(KERN_INFO "ext4_map_inode_page: error reading "
+					"block %ld\n", iblock);
+			goto out;
+		} else {
+			if (rc > 1)
+				WARN_ON(1);
+			rc = 0;
+		}
+		/* Unmap any metadata buffers from the block mapping, to avoid
+		 * data corruption due to direct-write from Lustre being
+		 * clobbered by a later flush of the blockdev metadata buffer.*/
+		if (map.m_flags & EXT4_MAP_NEW)
+			unmap_underlying_metadata(inode->i_sb->s_bdev,
+					map.m_pblk);
+		blocks[i] = map.m_pblk;
+	}
+
+out:
+	ext4_journal_stop(handle);
+	return rc;
+}
+EXPORT_SYMBOL(ext4_map_inode_page);