Re: [PATCH 4/7] xfuncs: Handle missing non-POSIX termios constants

[James Clarke <jrtc27@jrtc27.com>]

[Dropping debian-hurd@lists.debian.org as the Hurd defines all of them]

On 8 Oct 2017, at 12:18, Kang-Che Sung <explorer09@gmail.com> wrote:
> 2017年10月8日 18:50，"James Clarke" <jrtc27@jrtc27.com>寫道：
>> On 8 Oct 2017, at 02:34, Kang-Che Sung <explorer09@gmail.com> wrote:
>> > On Sun, Oct 8, 2017 at 1:53 AM, James Clarke <jrtc27@jrtc27.com> wrote:
>> >> diff --git a/libbb/xfuncs.c b/libbb/xfuncs.c
>> >> index 9cbfb2836..95dac656a 100644
>> >> --- a/libbb/xfuncs.c
>> >> +++ b/libbb/xfuncs.c
>> >> @@ -22,6 +22,16 @@
>> >>  */
>> >> #include "libbb.h"
>> >>
>> >> +#ifndef IMAXBEL
>> >> +# define IMAXBEL 0
>> >> +#endif
>> >> +#ifndef IUCLC
>> >> +# define IUCLC 0
>> >> +#endif
>> >> +#ifndef IXANY
>> >> +# define IXANY 0
>> >> +#endif
>> >> +
>> >
>> > I wonder, how do these break, and why does defining them as 0 solve the problem?
>> 
>> FreeBSD (well, GNU/kFreeBSD at least) does not define IUCLC. They are only used
>> in the line:
>> 
>> > newterm.c_iflag &= ~(BRKINT|INLCR|ICRNL|IXON|IXOFF|IUCLC|IXANY|IMAXBEL);
>> 
>> Thus, by defining them as 0 when not present, it is as if they were omitted
>> from that list, without needing a bunch of confusing #ifdef's in the expression
>> itself. While IMAXBEL and IXANY are defined everywhere Debian cares about, they
>> are still non-standard, so I did the same for them in case there is a platform
>> out there without them.
>> 
>> Regards,
>> James
> 
> 
> Why not just fix that usage line so that the bitwise OR's are all enclosed in #ifdef lines? I think it's better than defining the macros to a value that may cause further problems when reused.
> 
> Analogy: You probably won't define an unsupported signal, say SIGUSR3, to a zero value anyway. They are undefined for a reason. Hope you understand.

I can understand your reasoning; the only reason I did it that way was because
coreutils/stty.c has a whole load of instances of this, including for IMAXBEL,
IUCLC and IXANY, but looking at it more closely I now see that all uses of them
are in fact guarded by whether they are non-zero, so I'm not sure whether
there's really much point even for that file. I shall therefore change it to
use #ifdef's for the OR just like you said to avoid potential confusion.

Regards,
James