[PATCH] Add locking to iir(4): test or the driver will be removed

[John Baldwin]

This patch fixes various issues in the iir(4) driver and adds locking to make 
it MPSAFE.  The patch is against HEAD though I expect it probably applies to 
9 and 10 as well.  Please test with INVARIANTS enabled.

http://www.FreeBSD.org/~jhb/patches/iir_locking.patch

Note that this driver is using a deprecated API that will be removed in 11.  
If no one tests updates to this driver then it is not feasible to continue 
maintaining it in the tree.  In that case, it will be removed from HEAD one 
month from today.

-- 
John Baldwin