3 files changed, 80 insertions, 1 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 64edb09c481e..98760d14e2cd 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1068,6 +1068,7 @@ extern void ext4_set_aops(struct inode *inode);
 extern int ext4_writepage_trans_blocks(struct inode *);
 extern int ext4_block_truncate_page(handle_t *handle, struct page *page,
                 struct address_space *mapping, loff_t from);
+extern int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page);
 
 /* ioctl.c */
 extern long ext4_ioctl(struct file *, unsigned int, unsigned long);
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 4159be6366ab..b9510ba66a2d 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -123,6 +123,23 @@ force_commit:
         return ret;
 }
 
+static struct vm_operations_struct ext4_file_vm_ops = {
+        .fault          = filemap_fault,
+        .page_mkwrite   = ext4_page_mkwrite,
+};
+
+static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
+{
+        struct address_space *mapping = file->f_mapping;
+
+        if (!mapping->a_ops->readpage)
+                return -ENOEXEC;
+        file_accessed(file);
+        vma->vm_ops = &ext4_file_vm_ops;
+        vma->vm_flags |= VM_CAN_NONLINEAR;
+        return 0;
+}
+
 const struct file_operations ext4_file_operations = {
         .llseek         = generic_file_llseek,
         .read           = do_sync_read,
@@ -133,7 +150,7 @@ const struct file_operations ext4_file_operations = {
 #ifdef CONFIG_COMPAT
         .compat_ioctl   = ext4_compat_ioctl,
 #endif
-        .mmap           = generic_file_mmap,
+        .mmap           = ext4_file_mmap,
         .open           = generic_file_open,
         .release        = ext4_release_file,
         .fsync          = ext4_sync_file,
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;
+}