wait_on_bit — wait for a bit to be cleared
| int wait_on_bit ( | void * word, | 
| int bit, | |
| unsigned mode ); | 
wordthe word being waited on, a kernel virtual address
bitthe bit of the word being waited on
modethe task state to sleep in
   There is a standard hashed waitqueue table for generic use. This
   is the part of the hashtable's accessor API that waits on a bit.
   For instance, if one were to have waiters on a bitflag, one would
   call wait_on_bit in threads waiting for the bit to clear.
   One uses wait_on_bit where one is waiting for the bit to clear,
   but has no intention of setting it.
   Returned value will be zero if the bit was cleared, or non-zero
   if the process received a signal and the mode permitted wakeup
   on that signal.