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Date: Mon, 23 Mar 2009 00:39:37 -0400
From: David Schultz <das@FreeBSD.ORG>
To: Boris Kochergin <spawk@acm.poly.edu>
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Cc: freebsd-hackers@FreeBSD.ORG
Subject: Re: Doing away with NGROUPS_MAX in src/sys/sys/syslimits.h?
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On Sun, Mar 22, 2009, Boris Kochergin wrote:
> Ahoy. I got bitten by this today--a system I administer for someone had 
> users in more than 16 groups, so I had to bump the value, recompile the 
> kernel, and reboot. It seems desirable to (at the very least) make this 
> a read-only tunable that can be set using /boot/loader.conf, so as to 
> avoid source modification and kernel recompilation. I had a look around, 
> and noticed that NGROUPS_MAX is used to construct static arrays in a 
> couple of locations ("ibcs2_gid_t iset[NGROUPS_MAX];"). It seems that 
> malloc(9)/MALLOC(9) can be used to allocate memory for the array 
> instead, and panic() (or something) can be called if the allocation 
> fails, no? Is that about the gist of it? If I'm not overlooking 
> something major, I'd like to take a stab at it.

There's already a kern.ngroups sysctl, but there are many places
where `ngroups' needs to be used in preference to NGROUPS in the
kernel. In userland, sysconf(_SC_NGROUPS_MAX) needs to be used in
preference to NGROUPS_MAX.