linux-kernel - Re: [PATCH v3 5/5] tty: Use flow-control char function on closing path

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Date:   Mon, 11 Apr 2022 14:28:44 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     linux-serial@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-kernel@...r.kernel.org,
        Gilles Buloz <gilles.buloz@...tron.com>,
        Johan Hovold <johan@...nel.org>
Subject: Re: [PATCH v3 5/5] tty: Use flow-control char function on closing
 path

On Mon, Apr 11, 2022 at 12:48:59PM +0300, Ilpo Järvinen wrote:
> Use n_tty_receive_char_flow_ctrl also on the closing path. This makes
> the code cleaner and consistent.
> 
> However, there a small change of regression!
> 
> The earlier closing path has a small difference compared with the
> normal receive path. If START_CHAR and STOP_CHAR are equal, their
> precedence is different depending on which path a character is
> processed. I don't know whether this difference was intentional or
> not, and if equal START_CHAR and STOP_CHAR is actually used anywhere.
> But it feels not so useful corner case.
> 
> While this change would logically belong to those earlier changes,
> having a separate patch for this is useful. If this regresses, bisect
> can pinpoint this change rather than the large patch. Also, this
> change is not necessary to minimal fix for the issue addressed in
> the previous patch.

This is nice, if it flies!
FWIW,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> ---
>  drivers/tty/n_tty.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
> index fede29ed8daf..e6f47858f98f 100644
> --- a/drivers/tty/n_tty.c
> +++ b/drivers/tty/n_tty.c
> @@ -1414,15 +1414,10 @@ static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c,
>  		c = tolower(c);
>  
>  	if (I_IXON(tty)) {
> -		if (c == STOP_CHAR(tty)) {
> -			if (!lookahead_done)
> -				stop_tty(tty);
> -		} else if (c == START_CHAR(tty) && lookahead_done) {
> -			return;
> -		} else if (c == START_CHAR(tty) ||
> -			 (tty->flow.stopped && !tty->flow.tco_stopped && I_IXANY(tty) &&
> -			  c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) &&
> -			  c != SUSP_CHAR(tty))) {
> +		if (!n_tty_receive_char_flow_ctrl(tty, c, lookahead_done) &&
> +		    tty->flow.stopped && !tty->flow.tco_stopped && I_IXANY(tty) &&
> +		    c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) &&
> +		    c != SUSP_CHAR(tty)) {
>  			start_tty(tty);
>  			process_echoes(tty);
>  		}
> -- 
> 2.30.2
> 

-- 
With Best Regards,
Andy Shevchenko