Re: RLIMIT_NOFILE fallback

> Jeff King <peff@peff.net> writes:
>
>> That is, does sysconf actually work on such a system (or does it need a
>> similar run-time fallback)? And either way, we should try falling back
>> to OPEN_MAX rather than 1 if we have it.
>
> Interesting.
>
>> As far as the warning, I am not sure I see a point. The user does not
>> have any useful recourse, and git should continue to operate as normal.
>> Having every single git invocation print "by the way, RLIMIT_NOFILE does
>> not work on your system" seems like it would get annoying.
>
> Very true.  That makes the resulting function look like this:
>
>
> -------------------------------- 8< ------------------------------
>
> static unsigned int get_max_fd_limit(void)
> {
> #ifdef RLIMIT_NOFILE
> 	struct rlimit lim;
>
> 	if (!getrlimit(RLIMIT_NOFILE, &lim))
> 		return lim.rlim_cur;
> #endif
>
> #if defined(_SC_OPEN_MAX)
> 	{
> 		long sc_open_max = sysconf(_SC_OPEN_MAX);
> 		if (0 < sc_open_max)
> 			return sc_open_max;
> 	}

>
> #if defined(OPEN_MAX)
> 	return OPEN_MAX;
> #else
> 	return 1; /* see the caller ;-) */
> #endif
> }
>
> -------------------------------- >8 ------------------------------
>
>
> But the sysconf part makes me wonder; here is what we see in
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/sysconf.html
>
>     If name is an invalid value, sysconf() shall return -1 and set errno
>     to indicate the error. If the variable corresponding to name is
>     described in <limits.h> as a maximum or minimum value and the
>     variable has no limit, sysconf() shall return -1 without changing
>     the value of errno. Note that indefinite limits do not imply
>     infinite limits; see <limits.h>.
>
> For a broken system (like RLIMIT_NOFILE defined for the compiler,
> but the actual call returns a bogus error), the compiler may see the
> _SC_OPEN_MAX defined, while sysconf() may say "I've never heard of
> such a name" and return -1, or the system, whether broken or not,
> may want to say "Unlimited" and return -1.  The caller takes
> anything unreasonable as a positive value capped to 25 or something,
> so there isn't a real harm if we returned a bogus value from here,
> but I am not sure what the safe default behaviour of this function
> should be to help such a broken system while not harming systems
> that are functioning correctly.