Re: [PATCH] ntdll: Use the true maximum open FDs to set the limit on Mac.

[Brendan Shanks]

Hi Chip,
> On Apr 14, 2022, at 11:29 AM, Chip Davis  wrote:
>
> The actual upper limit is stored in the sysctl(3)
> "kern.maxfilesperproc". This value may be higher than the value of the
> OPEN_MAX constant.
>
> Using sysconf(3) with _SC_OPEN_MAX just returns the current value of
> RLIMIT_NOFILE, so that won't work here.
> Signed-off-by: Chip Davis
> Fixing this in the place it *actually* needs to be fixed this time...
>
> dlls/ntdll/unix/loader.c | 28 ++++++++++++++++++++++------
> 1 file changed, 22 insertions(+), 6 deletions(-)
>
> diff --git a/dlls/ntdll/unix/loader.c b/dlls/ntdll/unix/loader.c
> index d5867e4aa754..dc54a54a225f 100644
> --- a/dlls/ntdll/unix/loader.c
> +++ b/dlls/ntdll/unix/loader.c
> @@ -452,13 +452,29 @@ static void set_max_limit( int limit )
>         rlimit.rlim_cur = rlimit.rlim_max;
>         if (setrlimit( limit, &rlimit ) != 0)
>         {
> -#if defined(__APPLE__) && defined(RLIMIT_NOFILE) && defined(OPEN_MAX)
> -
>        /* On Leopard, setrlimit(RLIMIT_NOFILE, ...) fails on attempts to set
> -
>         * rlim_cur above OPEN_MAX (even if rlim_max > OPEN_MAX). */
> -
>        if (limit == RLIMIT_NOFILE && rlimit.rlim_cur > OPEN_MAX)
>
> +#if defined(__APPLE__) && defined(RLIMIT_NOFILE) && (defined(OPEN_MAX) || defined(KERN_MAXFILESPERPROC))

Are the OPEN_MAX/KERN_MAXFILESPERPROC ifdefs (and fallback to INT_MAX) necessary? KERN_MAXFILESPERPROC seems to have been present since 10.0 (https://github.com/apple-oss-distributions/xnu/blob/c1dac77fcd1f9be7193cad54...), and OPEN_MAX at least since 10.5 (https://github.com/apple-oss-distributions/xnu/blame/cc9a63552421e7db025ad77...).

Also, I tested this on macOS 12.4 on M1, and the initial setrlimit(RLIMIT_NOFILE, …) call actually succeeds, even though rlim_max is LONG_MAX, way larger than kern.maxfilesperproc. setrlimit() does fail on 10.13 though.
> -
>        if (limit == RLIMIT_NOFILE)
>       {
> -
>            rlimit.rlim_cur = OPEN_MAX;
> -
>            setrlimit( limit, &rlimit );
> -
>            /* On Leopard, setrlimit(RLIMIT_NOFILE, ...) fails on attempts to set
> -
>             * rlim_cur above OPEN_MAX (even if rlim_max > OPEN_MAX). */
> -
>            int open_max = INT_MAX;
>
> +#ifdef KERN_MAXFILESPERPROC
> -
>            /* This is the true OPEN_MAX; it may be greater than the constant.
> -
>             * sysconf(_SC_OPEN_MAX) won't work here: it just returns getrlimit(RLIMIT_NOFILE). */
> -
>            static int maxfilesperproc_oid[] = { CTL_KERN, KERN_MAXFILESPERPROC };
> -
>            size_t len = sizeof(open_max);
> -
>            if (sysctl(maxfilesperproc_oid, ARRAY_SIZE(maxfilesperproc_oid), &open_max, &len, NULL, 0) != 0)

Style nitpick: spaces around arguments.
> -
>                open_max = INT_MAX;
>
> +#endif
> +#ifdef OPEN_MAX
> -
>            if (open_max == INT_MAX)
> -
>                open_max = OPEN_MAX;
>
> +#endif
> -
>            if (rlimit.rlim_cur > open_max)
> -
>            {
> -
>                rlimit.rlim_cur = open_max;
> -
>                setrlimit( limit, &rlimit );
> -
>            }
>       }
>
> #endif
>         }
> -- 
> 2.34.1

Brendan