/* FS-Cache worker operation management routines
   *
   * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   *
   * See Documentation/filesystems/caching/operations.txt
   */
  
  #define FSCACHE_DEBUG_LEVEL OPERATION
  #include <linux/module.h>

  #include <linux/seq_file.h>

  #include <linux/slab.h>

  #include "internal.h"
  
  atomic_t fscache_op_debug_id;
  EXPORT_SYMBOL(fscache_op_debug_id);
  
  /**
   * fscache_enqueue_operation - Enqueue an operation for processing
   * @op: The operation to enqueue
   *
   * Enqueue an operation for processing by the FS-Cache thread pool.
   *
   * This will get its own ref on the object.
   */
  void fscache_enqueue_operation(struct fscache_operation *op)
  {
  	_enter("{OBJ%x OP%x,%u}",
  	       op->object->debug_id, op->debug_id, atomic_read(&op->usage));

  	ASSERT(list_empty(&op->pend_link));

  	ASSERT(op->processor != NULL);
  	ASSERTCMP(op->object->state, >=, FSCACHE_OBJECT_AVAILABLE);
  	ASSERTCMP(atomic_read(&op->usage), >, 0);

  	fscache_stat(&fscache_n_op_enqueue);
  	switch (op->flags & FSCACHE_OP_TYPE) {

  	case FSCACHE_OP_ASYNC:
  		_debug("queue async");

  		atomic_inc(&op->usage);

  		if (!queue_work(fscache_op_wq, &op->work))

  			fscache_put_operation(op);
  		break;

  	case FSCACHE_OP_MYTHREAD:
  		_debug("queue for caller's attention");
  		break;
  	default:
  		printk(KERN_ERR "FS-Cache: Unexpected op type %lx",
  		       op->flags);
  		BUG();
  		break;

  	}
  }
  EXPORT_SYMBOL(fscache_enqueue_operation);
  
  /*
   * start an op running
   */
  static void fscache_run_op(struct fscache_object *object,
  			   struct fscache_operation *op)
  {
  	object->n_in_progress++;
  	if (test_and_clear_bit(FSCACHE_OP_WAITING, &op->flags))
  		wake_up_bit(&op->flags, FSCACHE_OP_WAITING);
  	if (op->processor)
  		fscache_enqueue_operation(op);
  	fscache_stat(&fscache_n_op_run);
  }
  
  /*
   * submit an exclusive operation for an object
   * - other ops are excluded from running simultaneously with this one
   * - this gets any extra refs it needs on an op
   */
  int fscache_submit_exclusive_op(struct fscache_object *object,
  				struct fscache_operation *op)
  {
  	int ret;
  
  	_enter("{OBJ%x OP%x},", object->debug_id, op->debug_id);
  
  	spin_lock(&object->lock);
  	ASSERTCMP(object->n_ops, >=, object->n_in_progress);
  	ASSERTCMP(object->n_ops, >=, object->n_exclusive);

  	ASSERT(list_empty(&op->pend_link));

  
  	ret = -ENOBUFS;
  	if (fscache_object_is_active(object)) {
  		op->object = object;
  		object->n_ops++;
  		object->n_exclusive++;	/* reads and writes must wait */

  		if (object->n_ops > 1) {

  			atomic_inc(&op->usage);
  			list_add_tail(&op->pend_link, &object->pending_ops);
  			fscache_stat(&fscache_n_op_pend);
  		} else if (!list_empty(&object->pending_ops)) {
  			atomic_inc(&op->usage);
  			list_add_tail(&op->pend_link, &object->pending_ops);
  			fscache_stat(&fscache_n_op_pend);
  			fscache_start_operations(object);
  		} else {
  			ASSERTCMP(object->n_in_progress, ==, 0);
  			fscache_run_op(object, op);
  		}
  
  		/* need to issue a new write op after this */
  		clear_bit(FSCACHE_OBJECT_PENDING_WRITE, &object->flags);
  		ret = 0;
  	} else if (object->state == FSCACHE_OBJECT_CREATING) {
  		op->object = object;
  		object->n_ops++;
  		object->n_exclusive++;	/* reads and writes must wait */
  		atomic_inc(&op->usage);
  		list_add_tail(&op->pend_link, &object->pending_ops);
  		fscache_stat(&fscache_n_op_pend);
  		ret = 0;
  	} else {
  		/* not allowed to submit ops in any other state */
  		BUG();
  	}
  
  	spin_unlock(&object->lock);
  	return ret;
  }
  
  /*
   * report an unexpected submission
   */
  static void fscache_report_unexpected_submission(struct fscache_object *object,
  						 struct fscache_operation *op,
  						 unsigned long ostate)
  {
  	static bool once_only;
  	struct fscache_operation *p;
  	unsigned n;
  
  	if (once_only)
  		return;
  	once_only = true;
  
  	kdebug("unexpected submission OP%x [OBJ%x %s]",
  	       op->debug_id, object->debug_id,
  	       fscache_object_states[object->state]);
  	kdebug("objstate=%s [%s]",
  	       fscache_object_states[object->state],
  	       fscache_object_states[ostate]);
  	kdebug("objflags=%lx", object->flags);
  	kdebug("objevent=%lx [%lx]", object->events, object->event_mask);
  	kdebug("ops=%u inp=%u exc=%u",
  	       object->n_ops, object->n_in_progress, object->n_exclusive);
  
  	if (!list_empty(&object->pending_ops)) {
  		n = 0;
  		list_for_each_entry(p, &object->pending_ops, pend_link) {
  			ASSERTCMP(p->object, ==, object);
  			kdebug("%p %p", op->processor, op->release);
  			n++;
  		}
  
  		kdebug("n=%u", n);
  	}
  
  	dump_stack();
  }
  
  /*
   * submit an operation for an object
   * - objects may be submitted only in the following states:
   *   - during object creation (write ops may be submitted)
   *   - whilst the object is active
   *   - after an I/O error incurred in one of the two above states (op rejected)
   * - this gets any extra refs it needs on an op
   */
  int fscache_submit_op(struct fscache_object *object,
  		      struct fscache_operation *op)
  {
  	unsigned long ostate;
  	int ret;
  
  	_enter("{OBJ%x OP%x},{%u}",
  	       object->debug_id, op->debug_id, atomic_read(&op->usage));
  
  	ASSERTCMP(atomic_read(&op->usage), >, 0);
  
  	spin_lock(&object->lock);
  	ASSERTCMP(object->n_ops, >=, object->n_in_progress);
  	ASSERTCMP(object->n_ops, >=, object->n_exclusive);

  	ASSERT(list_empty(&op->pend_link));

  
  	ostate = object->state;
  	smp_rmb();
  
  	if (fscache_object_is_active(object)) {
  		op->object = object;
  		object->n_ops++;
  
  		if (object->n_exclusive > 0) {
  			atomic_inc(&op->usage);
  			list_add_tail(&op->pend_link, &object->pending_ops);
  			fscache_stat(&fscache_n_op_pend);
  		} else if (!list_empty(&object->pending_ops)) {
  			atomic_inc(&op->usage);
  			list_add_tail(&op->pend_link, &object->pending_ops);
  			fscache_stat(&fscache_n_op_pend);
  			fscache_start_operations(object);
  		} else {
  			ASSERTCMP(object->n_exclusive, ==, 0);
  			fscache_run_op(object, op);
  		}
  		ret = 0;
  	} else if (object->state == FSCACHE_OBJECT_CREATING) {
  		op->object = object;
  		object->n_ops++;
  		atomic_inc(&op->usage);
  		list_add_tail(&op->pend_link, &object->pending_ops);
  		fscache_stat(&fscache_n_op_pend);
  		ret = 0;

  	} else if (object->state == FSCACHE_OBJECT_DYING ||
  		   object->state == FSCACHE_OBJECT_LC_DYING ||
  		   object->state == FSCACHE_OBJECT_WITHDRAWING) {
  		fscache_stat(&fscache_n_op_rejected);
  		ret = -ENOBUFS;

  	} else if (!test_bit(FSCACHE_IOERROR, &object->cache->flags)) {
  		fscache_report_unexpected_submission(object, op, ostate);
  		ASSERT(!fscache_object_is_active(object));
  		ret = -ENOBUFS;
  	} else {
  		ret = -ENOBUFS;
  	}
  
  	spin_unlock(&object->lock);
  	return ret;
  }
  
  /*
   * queue an object for withdrawal on error, aborting all following asynchronous
   * operations
   */
  void fscache_abort_object(struct fscache_object *object)
  {
  	_enter("{OBJ%x}", object->debug_id);
  
  	fscache_raise_event(object, FSCACHE_OBJECT_EV_ERROR);
  }
  
  /*
   * jump start the operation processing on an object
   * - caller must hold object->lock
   */
  void fscache_start_operations(struct fscache_object *object)
  {
  	struct fscache_operation *op;
  	bool stop = false;
  
  	while (!list_empty(&object->pending_ops) && !stop) {
  		op = list_entry(object->pending_ops.next,
  				struct fscache_operation, pend_link);
  
  		if (test_bit(FSCACHE_OP_EXCLUSIVE, &op->flags)) {
  			if (object->n_in_progress > 0)
  				break;
  			stop = true;
  		}
  		list_del_init(&op->pend_link);

  		fscache_run_op(object, op);

  
  		/* the pending queue was holding a ref on the object */
  		fscache_put_operation(op);
  	}
  
  	ASSERTCMP(object->n_in_progress, <=, object->n_ops);
  
  	_debug("woke %d ops on OBJ%x",
  	       object->n_in_progress, object->debug_id);
  }
  
  /*

   * cancel an operation that's pending on an object
   */
  int fscache_cancel_op(struct fscache_operation *op)
  {
  	struct fscache_object *object = op->object;
  	int ret;
  
  	_enter("OBJ%x OP%x}", op->object->debug_id, op->debug_id);
  
  	spin_lock(&object->lock);
  
  	ret = -EBUSY;
  	if (!list_empty(&op->pend_link)) {
  		fscache_stat(&fscache_n_op_cancelled);
  		list_del_init(&op->pend_link);
  		object->n_ops--;
  		if (test_bit(FSCACHE_OP_EXCLUSIVE, &op->flags))
  			object->n_exclusive--;
  		if (test_and_clear_bit(FSCACHE_OP_WAITING, &op->flags))
  			wake_up_bit(&op->flags, FSCACHE_OP_WAITING);
  		fscache_put_operation(op);
  		ret = 0;
  	}
  
  	spin_unlock(&object->lock);
  	_leave(" = %d", ret);
  	return ret;
  }
  
  /*

   * release an operation
   * - queues pending ops if this is the last in-progress op
   */
  void fscache_put_operation(struct fscache_operation *op)
  {
  	struct fscache_object *object;
  	struct fscache_cache *cache;
  
  	_enter("{OBJ%x OP%x,%d}",
  	       op->object->debug_id, op->debug_id, atomic_read(&op->usage));
  
  	ASSERTCMP(atomic_read(&op->usage), >, 0);
  
  	if (!atomic_dec_and_test(&op->usage))
  		return;
  
  	_debug("PUT OP");
  	if (test_and_set_bit(FSCACHE_OP_DEAD, &op->flags))
  		BUG();
  
  	fscache_stat(&fscache_n_op_release);
  
  	if (op->release) {
  		op->release(op);
  		op->release = NULL;
  	}
  
  	object = op->object;

  	if (test_bit(FSCACHE_OP_DEC_READ_CNT, &op->flags))
  		atomic_dec(&object->n_reads);

  	/* now... we may get called with the object spinlock held, so we
  	 * complete the cleanup here only if we can immediately acquire the
  	 * lock, and defer it otherwise */
  	if (!spin_trylock(&object->lock)) {
  		_debug("defer put");
  		fscache_stat(&fscache_n_op_deferred_release);
  
  		cache = object->cache;
  		spin_lock(&cache->op_gc_list_lock);
  		list_add_tail(&op->pend_link, &cache->op_gc_list);
  		spin_unlock(&cache->op_gc_list_lock);
  		schedule_work(&cache->op_gc);
  		_leave(" [defer]");
  		return;
  	}
  
  	if (test_bit(FSCACHE_OP_EXCLUSIVE, &op->flags)) {
  		ASSERTCMP(object->n_exclusive, >, 0);
  		object->n_exclusive--;
  	}
  
  	ASSERTCMP(object->n_in_progress, >, 0);
  	object->n_in_progress--;
  	if (object->n_in_progress == 0)
  		fscache_start_operations(object);
  
  	ASSERTCMP(object->n_ops, >, 0);
  	object->n_ops--;
  	if (object->n_ops == 0)
  		fscache_raise_event(object, FSCACHE_OBJECT_EV_CLEARED);
  
  	spin_unlock(&object->lock);
  
  	kfree(op);
  	_leave(" [done]");
  }
  EXPORT_SYMBOL(fscache_put_operation);
  
  /*
   * garbage collect operations that have had their release deferred
   */
  void fscache_operation_gc(struct work_struct *work)
  {
  	struct fscache_operation *op;
  	struct fscache_object *object;
  	struct fscache_cache *cache =
  		container_of(work, struct fscache_cache, op_gc);
  	int count = 0;
  
  	_enter("");
  
  	do {
  		spin_lock(&cache->op_gc_list_lock);
  		if (list_empty(&cache->op_gc_list)) {
  			spin_unlock(&cache->op_gc_list_lock);
  			break;
  		}
  
  		op = list_entry(cache->op_gc_list.next,
  				struct fscache_operation, pend_link);
  		list_del(&op->pend_link);
  		spin_unlock(&cache->op_gc_list_lock);
  
  		object = op->object;
  
  		_debug("GC DEFERRED REL OBJ%x OP%x",
  		       object->debug_id, op->debug_id);
  		fscache_stat(&fscache_n_op_gc);
  
  		ASSERTCMP(atomic_read(&op->usage), ==, 0);
  
  		spin_lock(&object->lock);
  		if (test_bit(FSCACHE_OP_EXCLUSIVE, &op->flags)) {
  			ASSERTCMP(object->n_exclusive, >, 0);
  			object->n_exclusive--;
  		}
  
  		ASSERTCMP(object->n_in_progress, >, 0);
  		object->n_in_progress--;
  		if (object->n_in_progress == 0)
  			fscache_start_operations(object);
  
  		ASSERTCMP(object->n_ops, >, 0);
  		object->n_ops--;
  		if (object->n_ops == 0)
  			fscache_raise_event(object, FSCACHE_OBJECT_EV_CLEARED);
  
  		spin_unlock(&object->lock);
  
  	} while (count++ < 20);
  
  	if (!list_empty(&cache->op_gc_list))
  		schedule_work(&cache->op_gc);
  
  	_leave("");
  }
  
  /*

   * execute an operation using fs_op_wq to provide processing context -
   * the caller holds a ref to this object, so we don't need to hold one

   */

  void fscache_op_work_func(struct work_struct *work)

  {
  	struct fscache_operation *op =

  		container_of(work, struct fscache_operation, work);

  	unsigned long start;
  
  	_enter("{OBJ%x OP%x,%d}",
  	       op->object->debug_id, op->debug_id, atomic_read(&op->usage));
  
  	ASSERT(op->processor != NULL);
  	start = jiffies;
  	op->processor(op);
  	fscache_hist(fscache_ops_histogram, start);

  	fscache_put_operation(op);

  
  	_leave("");
  }