linux-kernel - Re: [PATCH v2 5/5] kdb: Tweak escape handling for vi users

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Message-ID: <CAD=FV=US8y=JrcQy3mB9MqFCaMd-N8FS2=JDe2zGWZhyHtTZtw@mail.gmail.com>
Date:   Tue, 8 Oct 2019 15:21:28 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Jason Wessel <jason.wessel@...driver.com>,
        kgdb-bugreport@...ts.sourceforge.net,
        LKML <linux-kernel@...r.kernel.org>,
        Patch Tracking <patches@...aro.org>
Subject: Re: [PATCH v2 5/5] kdb: Tweak escape handling for vi users

Hi,

On Tue, Oct 8, 2019 at 6:21 AM Daniel Thompson
<daniel.thompson@...aro.org> wrote:
>
> Currently if sequences such as "\ehelp\r" are delivered to the console then
> the h gets eaten by the escape handling code. Since pressing escape
> becomes something of a nervous twitch for vi users (and that escape doesn't
> have much effect at a shell prompt) it is more helpful to emit the 'h' than
> the '\e'.

I have no objection to this change.


> We don't simply choose to emit the final character for all escape sequences
> since that will do odd things for unsupported escape sequences (in
> other words we retain the existing behaviour once we see '\e[').

It's not like it handles unsupported escape sequences terribly well
anyway, of course.  As soon as if finds something it doesn't recognize
then it stops processing the escape sequence and will just interpret
the rest of it verbatim.  Like if I press Ctrl-Home on my keyboard I
see "5H" spit out, for instance.


> Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
> ---
>  kernel/debug/kdb/kdb_io.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
> index 288dd1babf90..b3fb88b1ee34 100644
> --- a/kernel/debug/kdb/kdb_io.c
> +++ b/kernel/debug/kdb/kdb_io.c
> @@ -158,8 +158,8 @@ static int kdb_getchar(void)
>
>                 *pbuf++ = key;
>                 key = kdb_read_handle_escape(buf, pbuf - buf);
> -               if (key < 0) /* no escape sequence; return first character */
> -                       return buf[0];
> +               if (key < 0) /* no escape sequence; return best character */
> +                       return buf[pbuf - buf != 2 ? 0 : 1];

optional nit: for me the inverse is easier to conceptualize, AKA:

buf[pbuf - buf == 2 ? 1 : 0];

-Doug