/* 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 "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));

        fscache_set_op_state(op, "EnQ");

        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_FAST:
                _debug("queue fast");
                atomic_inc(&op->usage);
                if (!schedule_work(&op->fast_work))
                        fscache_put_operation(op);
                break;
        case FSCACHE_OP_SLOW:
                _debug("queue slow");
                slow_work_enqueue(&op->slow_work);
                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)
{
        fscache_set_op_state(op, "Run");

        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);

        fscache_set_op_state(op, "SubmitX");

        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 > 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_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);

        fscache_set_op_state(op, "Submit");

        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;

        fscache_set_op_state(op, "Put");

        _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("");
}

/*
 * allow the slow work item processor to get a ref on an operation
 */
static int fscache_op_get_ref(struct slow_work *work)
{
        struct fscache_operation *op =
                container_of(work, struct fscache_operation, slow_work);

        atomic_inc(&op->usage);
        return 0;
}

/*
 * allow the slow work item processor to discard a ref on an operation
 */
static void fscache_op_put_ref(struct slow_work *work)
{
        struct fscache_operation *op =
                container_of(work, struct fscache_operation, slow_work);

        fscache_put_operation(op);
}

/*
 * execute an operation using the slow thread pool to provide processing context
 * - the caller holds a ref to this object, so we don't need to hold one
 */
static void fscache_op_execute(struct slow_work *work)
{
        struct fscache_operation *op =
                container_of(work, struct fscache_operation, slow_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);

        _leave("");
}

/*
 * describe an operation for slow-work debugging
 */
#ifdef CONFIG_SLOW_WORK_PROC
static void fscache_op_desc(struct slow_work *work, struct seq_file *m)
{
        struct fscache_operation *op =
                container_of(work, struct fscache_operation, slow_work);

        seq_printf(m, "FSC: OBJ%x OP%x: %s/%s fl=%lx",
                   op->object->debug_id, op->debug_id,
                   op->name, op->state, op->flags);
}
#endif

const struct slow_work_ops fscache_op_slow_work_ops = {
        .owner          = THIS_MODULE,
        .get_ref        = fscache_op_get_ref,
        .put_ref        = fscache_op_put_ref,
        .execute        = fscache_op_execute,
#ifdef CONFIG_SLOW_WORK_PROC
        .desc           = fscache_op_desc,
#endif
};