PerlIOBase_read(pTHX_ PerlIO *f, void *vbuf, Size_t count)
{
    STDCHAR *buf = (STDCHAR *) vbuf;
    if (f) {
        if (!(PerlIOBase(f)->flags & PERLIO_F_CANREAD)) {
            PerlIOBase(f)->flags |= PERLIO_F_ERROR;
            SETERRNO(EBADF, SS_IVCHAN);
            return 0;
        }
        ...