FS-Cache: Fix object state machine to have separate work and wait states

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: David Howells <dhowells@redhat.com>
Tested-By: Milosz Tanski <milosz@adfin.com>
Acked-by: Jeff Layton <jlayton@redhat.com>

1 files changed, 31 insertions, 35 deletions

diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index c5f92347cbf8..9ff516b1b9a0 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -328,11 +328,9 @@ struct fscache_cookie {
 #define FSCACHE_COOKIE_LOOKING_UP	0	/* T if non-index cookie being looked up still */
 #define FSCACHE_COOKIE_CREATING		1	/* T if non-index object being created still */
 #define FSCACHE_COOKIE_NO_DATA_YET	2	/* T if new object with no cached data yet */
-#define FSCACHE_COOKIE_PENDING_FILL	3	/* T if pending initial fill on object */
-#define FSCACHE_COOKIE_FILLING		4	/* T if filling object incrementally */
-#define FSCACHE_COOKIE_UNAVAILABLE	5	/* T if cookie is unavailable (error, etc) */
-#define FSCACHE_COOKIE_WAITING_ON_READS	6	/* T if cookie is waiting on reads */
-#define FSCACHE_COOKIE_INVALIDATING	7	/* T if cookie is being invalidated */
+#define FSCACHE_COOKIE_UNAVAILABLE	3	/* T if cookie is unavailable (error, etc) */
+#define FSCACHE_COOKIE_WAITING_ON_READS	4	/* T if cookie is waiting on reads */
+#define FSCACHE_COOKIE_INVALIDATING	5	/* T if cookie is being invalidated */
 };
 
 extern struct fscache_cookie fscache_fsdef_index;
@@ -341,45 +339,40 @@ extern struct fscache_cookie fscache_fsdef_index;
  * Event list for fscache_object::{event_mask,events}
  */
 enum {
-	FSCACHE_OBJECT_EV_REQUEUE,	/* T if object should be requeued */
+	FSCACHE_OBJECT_EV_NEW_CHILD,	/* T if object has a new child */
+	FSCACHE_OBJECT_EV_PARENT_READY,	/* T if object's parent is ready */
 	FSCACHE_OBJECT_EV_UPDATE,	/* T if object should be updated */
 	FSCACHE_OBJECT_EV_INVALIDATE,	/* T if cache requested object invalidation */
 	FSCACHE_OBJECT_EV_CLEARED,	/* T if accessors all gone */
 	FSCACHE_OBJECT_EV_ERROR,	/* T if fatal error occurred during processing */
-	FSCACHE_OBJECT_EV_RELEASE,	/* T if netfs requested object release */
-	FSCACHE_OBJECT_EV_RETIRE,	/* T if netfs requested object retirement */
-	FSCACHE_OBJECT_EV_WITHDRAW,	/* T if cache requested object withdrawal */
+	FSCACHE_OBJECT_EV_KILL,		/* T if netfs relinquished or cache withdrew object */
 	NR_FSCACHE_OBJECT_EVENTS
 };
 
 #define FSCACHE_OBJECT_EVENTS_MASK ((1UL << NR_FSCACHE_OBJECT_EVENTS) - 1)
 
 /*
+ * States for object state machine.
+ */
+struct fscache_transition {
+	unsigned long events;
+	const struct fscache_state *transit_to;
+};
+
+struct fscache_state {
+	char name[24];
+	char short_name[8];
+	const struct fscache_state *(*work)(struct fscache_object *object,
+					    int event);
+	const struct fscache_transition transitions[];
+};
+
+/*
  * on-disk cache file or index handle
  */
 struct fscache_object {
-	enum fscache_object_state {
-		FSCACHE_OBJECT_INIT,		/* object in initial unbound state */
-		FSCACHE_OBJECT_LOOKING_UP,	/* looking up object */
-		FSCACHE_OBJECT_CREATING,	/* creating object */
-
-		/* active states */
-		FSCACHE_OBJECT_AVAILABLE,	/* cleaning up object after creation */
-		FSCACHE_OBJECT_ACTIVE,		/* object is usable */
-		FSCACHE_OBJECT_INVALIDATING,	/* object is invalidating */
-		FSCACHE_OBJECT_UPDATING,	/* object is updating */
-
-		/* terminal states */
-		FSCACHE_OBJECT_DYING,		/* object waiting for accessors to finish */
-		FSCACHE_OBJECT_LC_DYING,	/* object cleaning up after lookup/create */
-		FSCACHE_OBJECT_ABORT_INIT,	/* abort the init state */
-		FSCACHE_OBJECT_RELEASING,	/* releasing object */
-		FSCACHE_OBJECT_RECYCLING,	/* retiring object */
-		FSCACHE_OBJECT_WITHDRAWING,	/* withdrawing object */
-		FSCACHE_OBJECT_DEAD,		/* object is now dead */
-		FSCACHE_OBJECT__NSTATES
-	} state;
-
+	const struct fscache_state *state;	/* Object state machine state */
+	const struct fscache_transition *oob_table; /* OOB state transition table */
 	int			debug_id;	/* debugging ID */
 	int			n_children;	/* number of child objects */
 	int			n_ops;		/* number of extant ops on object */
@@ -390,6 +383,7 @@ struct fscache_object {
 	spinlock_t		lock;		/* state and operations lock */
 
 	unsigned long		lookup_jif;	/* time at which lookup started */
+	unsigned long		oob_event_mask;	/* OOB events this object is interested in */
 	unsigned long		event_mask;	/* events this object is interested in */
 	unsigned long		events;		/* events to be processed by this object
 						 * (order is important - using fls) */
@@ -398,6 +392,10 @@ struct fscache_object {
 #define FSCACHE_OBJECT_LOCK		0	/* T if object is busy being processed */
 #define FSCACHE_OBJECT_PENDING_WRITE	1	/* T if object has pending write */
 #define FSCACHE_OBJECT_WAITING		2	/* T if object is waiting on its parent */
+#define FSCACHE_OBJECT_RETIRE		3	/* T if object should be retired */
+#define FSCACHE_OBJECT_IS_LIVE		4	/* T if object is not withdrawn or relinquished */
+#define FSCACHE_OBJECT_IS_LOOKED_UP	5	/* T if object has been looked up */
+#define FSCACHE_OBJECT_IS_AVAILABLE	6	/* T if object has become active */
 
 	struct list_head	cache_link;	/* link in cache->object_list */
 	struct hlist_node	cookie_link;	/* link in cookie->backing_objects */
@@ -415,8 +413,6 @@ struct fscache_object {
 	loff_t			store_limit_l;	/* current storage limit */
 };
 
-extern const char *fscache_object_states[];
-
 extern void fscache_object_init(struct fscache_object *, struct fscache_cookie *,
 				struct fscache_cache *);
 
@@ -431,7 +427,7 @@ extern void fscache_object_destroy(struct fscache_object *object);
 
 static inline bool fscache_object_is_live(struct fscache_object *object)
 {
-	return object->state < FSCACHE_OBJECT_DYING;
+	return test_bit(FSCACHE_OBJECT_IS_LIVE, &object->flags);
 }
 
 static inline bool fscache_object_is_dying(struct fscache_object *object)
@@ -441,7 +437,7 @@ static inline bool fscache_object_is_dying(struct fscache_object *object)
 
 static inline bool fscache_object_is_available(struct fscache_object *object)
 {
-	return object->state >= FSCACHE_OBJECT_AVAILABLE;
+	return test_bit(FSCACHE_OBJECT_IS_AVAILABLE, &object->flags);
 }
 
 static inline bool fscache_object_is_active(struct fscache_object *object)