linux-kernel - Re: [PATCH 2/2] kconfig: echo stdin to stdout if either is redirected

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Date:   Thu, 8 Feb 2018 08:05:39 +0100
From:   Ulf Magnusson <ulfalizer@...il.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Marc Herbert <marc.herbert@...el.com>
Subject: Re: [PATCH 2/2] kconfig: echo stdin to stdout if either is redirected

On Thu, Feb 8, 2018 at 7:51 AM, Ulf Magnusson <ulfalizer@...il.com> wrote:
> On Thu, Feb 8, 2018 at 7:35 AM, Ulf Magnusson <ulfalizer@...il.com> wrote:
>> On Thu, Feb 8, 2018 at 6:56 AM, Masahiro Yamada
>> <yamada.masahiro@...ionext.com> wrote:
>>> If stdio is not tty, conf_askvalue() puts additional new line to
>>> prevent prompts are all concatenated into a single line.  This care
>>> is missing in conf_choice(), so a 'choice' prompt and the next prompt
>>> are shown in the same line.
>>>
>>> Move the code into xfgets() to take care of all cases.  To improve
>>> this more, echo stdin to stdout.  This clarifies what keys were input
>>> from stdio and the stdout looks like as if it were from tty.
>>>
>>> I removed the isatty(2) check since stderr is unrelated here.
>>>
>>> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>>> ---
>>>
>>>  scripts/kconfig/conf.c | 7 ++++---
>>>  1 file changed, 4 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/scripts/kconfig/conf.c b/scripts/kconfig/conf.c
>>> index 358e2e4..c5318d3 100644
>>> --- a/scripts/kconfig/conf.c
>>> +++ b/scripts/kconfig/conf.c
>>> @@ -76,6 +76,9 @@ static void xfgets(char *str, int size, FILE *in)
>>>  {
>>>         if (!fgets(str, size, in))
>>>                 fprintf(stderr, "\nError in reading or end of file.\n");
>>> +
>>> +       if (!tty_stdio)
>>> +               printf("%s", str);
>>>  }
>>>
>>>  static int conf_askvalue(struct symbol *sym, const char *def)
>>> @@ -106,8 +109,6 @@ static int conf_askvalue(struct symbol *sym, const char *def)
>>>         case oldaskconfig:
>>>                 fflush(stdout);
>>>                 xfgets(line, sizeof(line), stdin);
>>> -               if (!tty_stdio)
>>> -                       printf("\n");
>>>                 return 1;
>>>         default:
>>>                 break;
>>> @@ -495,7 +496,7 @@ int main(int ac, char **av)
>>>         bindtextdomain(PACKAGE, LOCALEDIR);
>>>         textdomain(PACKAGE);
>>>
>>> -       tty_stdio = isatty(0) && isatty(1) && isatty(2);
>>> +       tty_stdio = isatty(0) && isatty(1);
>>>
>>>         while ((opt = getopt_long(ac, av, "s", long_opts, NULL)) != -1) {
>>>                 if (opt == 's') {
>>> --
>>> 2.7.4
>>>
>>
>> Reviewed-by: Ulf Magnusson <ulfalizer@...il.com>
>>
>> Might be some case I'm not thinking of, but wouldn't it make sense to
>> just check isatty(1) as well? If stdout is a regular file, it seems
>> it'd be nice to have the input appear there, regardless of where stdin
>> is from.
>>
>> Maybe the tty_stdio variable could be removed then as well, replaced
>> with just 'if (!isatty(1))'.
>>
>> Cheers,
>> Ulf
>
> Hmm... if stdout is a tty and stdin isn't, this would prevent the
> input from showing up on the terminal though, so I guess it makes
> sense. That case seems more important than the weird
> stdin=tty/stdout=file case.
>
> Tricky stuff. :)
>
> Cheers,
> Ulf

Oh... and that one's already taken care of too, reading closer.

stdin | stdout | wants stdin written to stdout
------+--------+-------------------------------------
tty   | tty    | no (already echoed by tty)
tty   | file   | yes (echoed by tty, written to file)
file  | tty    | yes (not echoed by tty)
file  | file   | yes

So !(tty(0) && tty(1)) makes sense. Excuse the rambling...

Cheers,
Ulf