• David Howells's avatar
    FS-Cache: Fix object state machine to have separate work and wait states · caaef690
    David Howells authored
    Fix object state machine to have separate work and wait states as that makes
    it easier to envision.
    
    There are now three kinds of state:
    
     (1) Work state.  This is an execution state.  No event processing is performed
         by a work state.  The function attached to a work state returns a pointer
         indicating the next state to which the OSM should transition.  Returning
         NO_TRANSIT repeats the current state, but goes back to the scheduler
         first.
    
     (2) Wait state.  This is an event processing state.  No execution is
         performed by a wait state.  Wait states are just tables of "if event X
         occurs, clear it and transition to state Y".  The dispatcher returns to
         the scheduler if none of the events in which the wait state has an
         interest are currently pending.
    
     (3) Out-of-band state.  This is a special work state.  Transitions to normal
         states can be overridden when an unexpected event occurs (eg. I/O error).
         Instead the dispatcher disables and clears the OOB event and transits to
         the specified work state.  This then acts as an ordinary work state,
         though object->state points to the overridden destination.  Returning
         NO_TRANSIT resumes the overridden transition.
    
    In addition, the states have names in their definitions, so there's no need for
    tables of state names.  Further, the EV_REQUEUE event is no longer necessary as
    that is automatic for work states.
    
    Since the states are now separate structs rather than values in an enum, it's
    not possible to use comparisons other than (non-)equality between them, so use
    some object->flags to indicate what phase an object is in.
    
    The EV_RELEASE, EV_RETIRE and EV_WITHDRAW events have been squished into one
    (EV_KILL).  An object flag now carries the information about retirement.
    
    Similarly, the RELEASING, RECYCLING and WITHDRAWING states have been merged
    into an KILL_OBJECT state and additional states have been added for handling
    waiting dependent objects (JUMPSTART_DEPS and KILL_DEPENDENTS).
    
    A state has also been added for synchronising with parent object initialisation
    (WAIT_FOR_PARENT) and another for initiating look up (PARENT_READY).
    Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
    Tested-By: default avatarMilosz Tanski <milosz@adfin.com>
    Acked-by: default avatarJeff Layton <jlayton@redhat.com>
    caaef690
object-list.c 11.9 KB