linux-kernel - Re: [PATCH] kdb: Fix incorrect naming of history arrow keys in code

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Message-ID: <20241101183418.GB752705@aspen.lan>
Date: Fri, 1 Nov 2024 18:34:18 +0000
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Doug Anderson <dianders@...omium.org>
Cc: Nir Lichtman <nir@...htman.org>, jason.wessel@...driver.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kdb: Fix incorrect naming of history arrow keys in code

On Fri, Nov 01, 2024 at 08:29:39AM -0700, Doug Anderson wrote:
> Hi,
>
> On Thu, Oct 31, 2024 at 5:26 PM Nir Lichtman <nir@...htman.org> wrote:
> >
> > On Thu, Oct 31, 2024 at 04:06:03PM -0700, Doug Anderson wrote:
> > > >
> > > > kdb doesn't react to ctrl p and n, and following the code flow with GDB
> > > > reveals that these values map to the up and down arrows.
> > >
> > > Really? kdb reacts to "ctrl-P" and "ctrl-N" for me. It also reacts to
> > > "ctrl-F" and "ctrl-B".
> > >
> >
> > Interesting, how do you run kdb? I use the kgdboc=kbd kernel boot param.
> > I haven't checked with serial as the console since I work with the keyboard,
> > but if serial does go through this using ctrl+p/n then the code in the
> > current state is misleading since the keys change depending on the I/O method.
>
> Wow, I've never used the keyboard method since I've never run kdb on a
> machine that supports it. :-P
>
>
> > Evidence in the code for usage of arrow keys in the case of keyboard can
> > be seen by examining kdb_read in kernel/debug/kdb/kdb_io.c, in the /* Down */
> > and /* Up */ cases the values 14 and 16 can be seen.
>
> Right. Essentially the logic is converting the Up and Down sequences
> to the characters Ctrl-P and Ctrl-N. ...so by the time we get to
> handle_ctrl_cmd() the characters really are Ctrl commands, not arrow
> commands. Thus handle_ctrl_cmd() is correct as is.

Those comments, which I'm pretty sure I added, are arguably more a
reminder about how the input systems map up/down (which on serial are
multi-byte escape sequences) into single character control codes.


> > Do you suggest to keep as is or to work on a patch with a more generic name that
> > would fit both?
>
> IMO it's a bug that the keyboard code isn't properly reporting Ctrl-N
> and Ctrl-P. Does it handle other Ctrl characters? Ctrl-A should go to
> the start of the line and Ctrl-E the end. Maybe you can track down why
> this isn't happening?

I'm with Doug on this one. What values does the kdb code generate
Ctrl-<letter>? IMHO it should be generating 14 for ctrl-N and 16 for
ctrl-P.

BTW ctrl-N and ctrl-P are very common keystrokes for command line
history (try them in any readline program such as bash).


Daniel.