staging/lustre/clio: cl_lock simplification

staging/lustre/clio: cl_lock simplification

In this patch, the cl_lock cache is eliminated. cl_lock is turned
into a cacheless data container for the requirements of locks to
complete the IO. cl_lock is created before I/O starts and destroyed
when the I/O is complete.

cl_lock depends on LDLM lock to fulfill lock semantics. LDLM lock
is attached to cl_lock at OSC layer. LDLM lock is still cacheable.

Two major methods are supported for cl_lock: clo_enqueue and
clo_cancel.  A cl_lock is enqueued by cl_lock_request(), which will
call clo_enqueue() methods for each layer to enqueue the lock.
At the LOV layer, if a cl_lock consists of multiple sub cl_locks,
each sub locks will be enqueued correspondingly. At OSC layer, the
lock enqueue request will tend to reuse cached LDLM lock; otherwise
a new LDLM lock will have to be requested from OST side.

cl_lock_cancel() must be called to release a cl_lock after use.
clo_cancel() method will be called for each layer to release the
resource held by this lock. At OSC layer, the reference count of LDLM
lock, which is held at clo_enqueue time, is released.

LDLM lock can only be canceled if there is no cl_lock using it.

Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-on: http://review.whamcloud.com/10858
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3259
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>