1 files changed, 61 insertions, 0 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c5d506dce8c5..034fc544aa66 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3564,3 +3564,64 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
 
         return err;
 }
+
+static int ext4_bh_unmapped(handle_t *handle, struct buffer_head *bh)
+{
+        return !buffer_mapped(bh);
+}
+
+int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+{
+        loff_t size;
+        unsigned long len;
+        int ret = -EINVAL;
+        struct file *file = vma->vm_file;
+        struct inode *inode = file->f_path.dentry->d_inode;
+        struct address_space *mapping = inode->i_mapping;
+
+        /*
+         * Get i_alloc_sem to stop truncates messing with the inode. We cannot
+         * get i_mutex because we are already holding mmap_sem.
+         */
+        down_read(&inode->i_alloc_sem);
+        size = i_size_read(inode);
+        if (page->mapping != mapping || size <= page_offset(page)
+            || !PageUptodate(page)) {
+                /* page got truncated from under us? */
+                goto out_unlock;
+        }
+        ret = 0;
+        if (PageMappedToDisk(page))
+                goto out_unlock;
+
+        if (page->index == size >> PAGE_CACHE_SHIFT)
+                len = size & ~PAGE_CACHE_MASK;
+        else
+                len = PAGE_CACHE_SIZE;
+
+        if (page_has_buffers(page)) {
+                /* return if we have all the buffers mapped */
+                if (!walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
+                                       ext4_bh_unmapped))
+                        goto out_unlock;
+        }
+        /*
+         * OK, we need to fill the hole... Do write_begin write_end
+         * to do block allocation/reservation.We are not holding
+         * inode.i__mutex here. That allow * parallel write_begin,
+         * write_end call. lock_page prevent this from happening
+         * on the same page though
+         */
+        ret = mapping->a_ops->write_begin(file, mapping, page_offset(page),
+                        len, AOP_FLAG_UNINTERRUPTIBLE, &page, NULL);
+        if (ret < 0)
+                goto out_unlock;
+        ret = mapping->a_ops->write_end(file, mapping, page_offset(page),
+                        len, len, page, NULL);
+        if (ret < 0)
+                goto out_unlock;
+        ret = 0;
+out_unlock:
+        up_read(&inode->i_alloc_sem);
+        return ret;
+}