Programming

int myNewfs_write_begin(struct file *file, struct address_space *mapping,
                             loff_t pos, unsigned len, unsigned flags,
                             struct page **pagep, void **fsdata) {

         struct inode *inode = mapping->host;
         int ret, error, retStatus;
         int retries = 0;
         struct page *page;
         pgoff_t index;
         unsigned from, to;
         int needed_blocks = ext3_writepage_trans_blocks(inode) + 1;
         ret = 0;
         error = 0;
         retries = 0;
         index = pos >> PAGE_CACHE_SHIFT;
         from = pos & (PAGE_CACHE_SIZE - 1);
         to = from + len;
   
    findpage:
             page=NULL;
             page = grab_cache_page_write_begin(mapping, index, flags);
             if (!page) {
                  return -ENOMEM;
             }
              /*
              ** Calling the original _My_OldFS_prepare_write.
              ** The call ensures the same old handling of
              ** the filesystem wraped with the new VFS APIs.
              */
              *pagep = page;
              retStatus = _My_OldFS_prepare_write(file, page, from, to);
    return retStatus;
}

//Similarly,

int _myNewfs_write_end(struct file *file, struct address_space *mapping, loff_t pos, unsigned len, unsigned copied,
                     struct page *page, void *fsdata) {

         unsigned start, ret;
         start = pos & (PAGE_CACHE_SIZE - 1);
         struct inode *inode = mapping->host;
         /* This could be a short (even 0-length) commit */
         ret = 0;
         /*
         ** Calling OLD Commit Write.
         */
         ret = _myOldFS_commit_write(file, page, start, start+copied);
         /*
         ** Update the radix page ref count.
         */
         //mapping->nrpages--;
         /*
         ** Unlock the page, locked from the write_begin.
         */
          unlock_page(page);
         /*
         ** Release the page.
         */
         //flush_dcache_page(page);
         page_cache_release(page);
         return ret? ret : copied;
}