generic_file_write_iter — write data to a file
| ssize_t generic_file_write_iter ( | struct kiocb * iocb, | 
| struct iov_iter * from ); | 
   This is a wrapper around __generic_file_write_iter to be used by most
   filesystems. It takes care of syncing the file in case of O_SYNC file
   and acquires i_mutex as needed.