p9_client_write
len = p9_client_write(fid, subreq->start, &subreq->io_iter, &err);
p9_client_write(fid, 0, &from, &retval);
int p9_client_write(struct p9_fid *fid, u64 offset, struct iov_iter *from, int *err);
EXPORT_SYMBOL(p9_client_write);