linux-kernel - Re: [PATCH 3/4] auxdisplay: charlcd: fix x/y address commands

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Date:   Mon, 26 Feb 2018 23:29:14 +0100
From:   Robert Abel <rabel@...ertabel.eu>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Willy Tarreau <w@....eu>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH 3/4] auxdisplay: charlcd: fix x/y address commands

Hi Geert,

On 26 Feb 2018 09:46, Geert Uytterhoeven wrote:
>> +
>> +               nxt_cmd = *esc++;
>> +               nxt_esc = esc;
>> +
>> +               while ('\0' != *esc) {
>> +
>> +                       cmd = nxt_cmd;
>> +                       esc = nxt_esc;
>> +                       nxt_esc = strpbrk(esc, "xy;");
>> +                       if (NULL != nxt_esc) {
>> +                               nxt_cmd = *nxt_esc;
>> +                               /* terminate current sequence with NUL */
>> +                               *nxt_esc++ = '\0';
>> +                       }
> 
> So if none of "x", "y", or ";" is found, nxt_cmd will still contain
> the current command?
> Shouldn't it be reset to '\0' or so?

I originally had a comment there, but it then felt kinda silly.
Since one of the conditions of the code is that a semicolon ';' is
detected at the end of the stream, the situation you describe never
occurs until the end of the command string.

nxt_esc == NULL only when cmd == ';' and *esc == NULL. Since there is
nothing to terminate and the code won't run again (due to while (*esc)),
I didn't reset nxt_cmd. Other than that, I also don't know that there is
a sensible reset value.

Regards,

Robert