Description of problem:
irqbalance uses the topology information from /sys/devices/system/cpu.  I
noticed that when reading the hierarchy irqbalance tries to open nonsense files like

  /sys/devices/system/cpu/cpuidle/online

This is due to an incomplete check when reading the directory
/sys/devices/system/cpu.  The code only checks for a substring "cpu" to be
available.

Once I fixed that I noticed that irqbalance doesn't access these files after the
startup anymore.  This is probably due to the fact that recognizing "cpuidle" as
a real CPU the CPU count is thrown off.  I haven't investigated this further. 
But this little inefficiency is in fact a real bug.

While I was at it I rewrote a large amount of inefficient code.  openat() saves
creating path strings and reduces the lookup times.  Not creating a new string
for each getline call saves overhead related to memory handling.


Version-Release number of selected component (if applicable):
irqbalance-0.55-4.fc8.x86_64

How reproducible:
always (I guess)

Steps to Reproduce:
1.start irqbalance
2.attach to it using strace or use a systemtap script monitoring open calls
3.
  
Actual results:
Lots of reloading the /sys/devices/system/cpu/ hierarchy and looking for
/sys/devices/system/cpu/cpuidle/online etc.

Expected results:
Infrequent (none after startup?) parsing of the hierarchy.  Don't look into
/sys/devices/system/cpu/cpuidle/ at all.

Additional info:

This patch should probably also be added to RHEL5 and F7.