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

[John Baldwin]

This patch adds locking to mcd(4) and marks it MPSAFE.  This patch is against 
HEAD but probably applies to 9 and 10 as well.  Please enable INVARIANTS while 
testing.

http://www.FreeBSD.org/~jhb/patches/mcd_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