All,

Here is a set of patches (against a recent-ish 2.5 BK) that removes the 
arbitrary limit of 32 groups.

The first patch creates generic qsort() and bsearch() routines (I have 
another patch to conver XFS to use it, as discussed with Christoph a 
while back).

The second patch converts task->groups[] into a dynamic, refcounted, CoW 
array.  It does the needed bits for i386 (minor) but not the other 
architectures.  I have (not included here for brevity) patches that 
convert other arch trees to do the right thing (I think) and convert 
other usages of NGROUPS and task->groups and task->ngroups.  There are 
still a few issues I am working out with those.

I wanted to post this (and CC: people who have mailed me about it) and 
see if there are any complaints about the approach.  The patches are 
simple, and have been in use in our own 2.4.x systems or some time.  I 
did make some changes in forward porting, but they are tested on at 
least one 2.5.x box here :)

This has the side effect of reducing the size of struct task_struct by a 
bit, too. :)

This should run on any glibc, without mods.  Glibc will need to return a 
different value instead of NGROUPS (32), to be fully correct, though.  I 
suggest INT_MAX :)

We've found a couple apps that needed to be fixed up in the event of >32 
groups being used, and when this goes mainline, we'll pop out those 
patches, too.  Another issue:  this changes /proc/pid/status to only 
show 32 groups - not sure what better solution is preferred.

Comments, read-overs, and flames requested.  Ideally I'd like to see 
this go into 2.5.x real soon now. :)

Tim
-- 
Tim Hockin
Systems Software Engineer
Sun Microsystems, Linux Kernel Engineering
thockin@sun.com