If the entry is found in name cache, cache_lookup() does all the
necessary locking now, simplifying the interface and making the
code easier to follow and maintain.
The code now also removes the entry from cache when it's either invalid
(vget() fails) or the vnode has been recycled while waiting for the lock.
In that case, unlock/relock of the directory vnode has been eliminated too.
Both changes could lead to sligh performace improvement in same cases.
Furthermore, obscure bug has been found and eliminated for ISDOTDOT in the
lockparent && ISLASTCN case: if the vget() succeded and the re-lock
of the directory vnode not, we returned the error with the '..' vnode still
locked.
For simplicity, cache_lookup() now returns 0 if the positive entry was found
in cache, -1 if not found and ENOENT or error returned by the locking
functions in any other case.
Many thanks to Bill Studenmund and especially Charles Hannum
for invaluable advices and code to get this right.
Tested by: jdolecek
Rewieved by: wrstuden, mycroft
026b142488