Re: interix 3.5 select bug

[Jim Meyering]

Bruno Haible wrote:
> Simon Josefsson wrote:
>> > It seems that another solution would be to
>> > detect this problem, and to replace select if the system's select
>> > doesn't work.
>
> Good point. Using 0 as nfd argument is common; try searching for
> " = select (0, " on http://www.google.com/codesearch/.
>
>> I haven't studied the spec enough to say
>
> That's easy to do:
> <http://www.opengroup.org/onlinepubs/9699919799/functions/select.html>
> says:
>   "The nfds argument specifies the range of descriptors to be tested.
>    The first nfds descriptors shall be checked in each set; that is,
>    the descriptors from zero through nfds-1 in the descriptor sets shall
>    be examined."
> In other words, there is no requirement that nfds be > 0. nfds = 0 is valid.
>
>> However, technically the configure-time test would have
>> to be one that runs a binary, to determine if select fails
>> like that.  and that's ugly...
>
> Sure it will be a test with AC_TRY_RUN. What is ugly about it? For
> cross-compiling we can use AC_CANONICAL_HOST and dispatch on that,
> as usual.
>
> Here is a series of two proposed patches to provide a workaround.
> Simon, is that OK to commit?
>
>
> 2009-03-12  Bruno Haible  <address@hidden>
>
>       * lib/select.c: Renamed from lib/winsock-select.c.
>       * modules/select (Files): Add lib/select.c, remove
>       lib/winsock-select.c.
>       (configure.ac): Update.

Thanks for doing the work!
Only one question:

> --- lib/select.c.orig 2009-03-12 11:36:40.000000000 +0100
...
> +int
> +rpl_select (int nfds, fd_set *rfds, fd_set *wfds, fd_set *xfds,
> +            struct timeval *timeout)
> +{
> +  /* Interix 3.5 has a bug: it does not support nfds == 0.  */
> +  if (nfds == 0)
> +    {
> +      nfds = 1;
> +      rfds = NULL;
> +      wfds = NULL;
> +      xfds = NULL;
> +    }

Did you consider doing the above only when all three input pointers
are NULL?  I have a slight preference not to map the suspicious
combination of nfds==0 and one or more non-NULL pointer arg.
to arguments that provoke no diagnostic on that system.