[Mauiusers] something wrong in class node features code

Garrick Staples garrick at usc.edu
Mon Oct 27 19:24:20 MDT 2008

I've been highly dependant on Maui's "neednodes" feature with torque classes
for many years.  We have lots of queues that divide up nearly 2700 nodes.
Recently, when I added a new queue, maui started doing the Wrong Thing.

It started adding random node features to class' configs, ie:
$ showconfig | grep CLASS

Where "X4100" isn't supposed to be there.  I was really baffled.  I've been
doing this for years, only making adjustments here and there as we added more
nodes and queues.

After walking the code a bit, I came across this bit that initially made me
suspect a 64bit problem, but I just get more confused the more I look at it:

MClass.c:MClassSetAttr() calls 
     (DefFBM is an array of ints)

MUtil.c:MUGetMAttr(...,int *AttrMap, int MapSize) calls
  MUBMClear(AttrMap,(MapSize << 3));

And MUBMClear is a define:
  #define MUBMClear(M,S) memset(M,0,sizeof(int) * ((S >> 5) + 1))

Why is the passed size of the array messed with so much?  I don't understand
what is happening.  A perfectly respectable 'sizeof(C->DefFBM)' turns into this
monstrosity by the time it gets to memset():
  sizeof(int) * ((((sizeof(C->DefFBM)) << 3) >> 5) + 1)

As it turns out, a 32bit build doesn't show the problem.  I'm now using a 32bit
on my 64bit server as a work-around.   I don't actually think this is a 64bit
problem, or if it is even my problem; but this code does seem wrong.

Now that I think about it, I think just the '+1' is messing it up (as long as
the assumption that sizeof(int)==4 holds up).

Oh, and this is the latest snapshot: maui-3.2.6p20-snap.1223069659.

Garrick Staples, GNU/Linux HPCC SysAdmin
University of Southern California

Please avoid sending me Word or PowerPoint attachments.
See http://www.gnu.org/philosophy/no-word-attachments.html
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