linux-kernel - Re: [PATCH v2 1/5] kdb: Tidy up code to handle escape sequences

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Date:   Tue, 8 Oct 2019 15:20:30 -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 1/5] kdb: Tidy up code to handle escape sequences

Hi,

On Tue, Oct 8, 2019 at 6:21 AM Daniel Thompson
<daniel.thompson@...aro.org> wrote:
>
> kdb_read_get_key() has extremely complex break/continue control flow
> managed by state variables and is very hard to review or modify. In
> particular the way the escape sequence handling interacts with the
> general control flow is hard to follow. Separate out the escape key
> handling, without changing the control flow. This makes the main body of
> the code easier to review.
>
> Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
> ---
>  kernel/debug/kdb/kdb_io.c | 127 ++++++++++++++++++++------------------
>  1 file changed, 66 insertions(+), 61 deletions(-)
>
> diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
> index 3a5184eb6977..68e2c29f14f5 100644
> --- a/kernel/debug/kdb/kdb_io.c
> +++ b/kernel/debug/kdb/kdb_io.c
> @@ -49,6 +49,63 @@ static int kgdb_transition_check(char *buffer)
>         return 0;
>  }
>
> +/*
> + * kdb_read_handle_escape
> + *
> + * Run a validity check on an accumulated escape sequence.
> + *
> + * Returns -1 if the escape sequence is unwanted, 0 if it is incomplete,
> + * otherwise it returns a mapped key value to pass to the upper layers.
> + */
> +static int kdb_read_handle_escape(char *buf, size_t sz)
> +{
> +       char *lastkey = buf + sz - 1;
> +
> +       switch (sz) {
> +       case 1:
> +               if (*lastkey == '\e')
> +                       return 0;

Technically the "if" here isn't needed, at least not until a later
patch in the series.  The only way we could get here is if *lastkey ==
'\e'...

...but I suppose it's fine to keep it here in preparation for the last patch.

Reviewed-by: Douglas Anderson <dianders@...omium.org>