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

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: [patch 16/20] XEN-paravirt: Add the Xen virtual console driver.
From: Alan <alan@xxxxxxxxxxxxxxxxxxx>
Date: 2007年1月14日 00:37:52 +0000
Cc: Andrew Morton <akpm@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Ian Pratt <ian.pratt@xxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
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> +#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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