[Xen-devel] Re: [patch 16/20] XEN-paravirt: Add the Xen virtual console driver.

[Alan <alan@xxxxxxxxxxxxxxxxxxx>]

> +#endif
> +             tty_insert_flip_char(xencons_tty, buf[i], 0);

Please use the defines like TTY_NORMAL not just 0. 

> +             if ((xencons_tty->flags & (1 << TTY_DO_WRITE_WAKEUP)) &&
> +                 (xencons_tty->ldisc.write_wakeup != NULL))
> +                     (xencons_tty->ldisc.write_wakeup)(xencons_tty);
> +     }

You are't allowed to derefence and call ldisc methods without
holding the lock. You can replace that chunk with a call to the helper
function tty_wakeup(tty). Small but real race condition otherwise as you
xencons_tty->ldisc may be changing as you call it.

> +static inline int __xencons_put_char(int ch)
> +{
> +     char _ch = (char)ch;
> +     if ((wp - wc) == wbuf_size)
> +             return 0;
> +     wbuf[WBUF_MASK(wp++)] = _ch;
> +     return 1;
> +}

A lot of very confusing sign stuff here - you turn an int into a char and
put it into a uchar array

> +     for (i = 0; i < count; i++)
> +             if (!__xencons_put_char(buf[i]))
> +                     break;

The int coming from a uchar array

Don't think its wrong - just acutely weird and perhaps could be tidier

> +static void xencons_close(struct tty_struct *tty, struct file *filp)
> +{
> +     unsigned long flags;
> +
> +     mutex_lock(&tty_mutex);

It would be good in future if you could avoid using tty_mutex and use a
private lock. At the moment vt "borrows" it and there are a couple of
incestuous spots but the plan is to eventually fix them and make it
private to tty_io.


Andrew: No objection to this tty stuff being merged provided the bugs
noted above (not worried about the sign stuff) are fixed before it goes
on to Linus.

Alan

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