/*
 * Functions related to softirq rq completions
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/interrupt.h>
#include <linux/cpu.h>
#include <linux/sched.h>

#include "blk.h"

static DEFINE_PER_CPU(struct list_head, blk_cpu_done);

/*
 * Softirq action handler - move entries to local list and loop over them
 * while passing them to the queue registered handler.
 */
static void blk_done_softirq(struct softirq_action *h)
{
        struct list_head *cpu_list, local_list;

        local_irq_disable();
        cpu_list = this_cpu_ptr(&blk_cpu_done);
        list_replace_init(cpu_list, &local_list);
        local_irq_enable();

        while (!list_empty(&local_list)) {
                struct request *rq;

                rq = list_entry(local_list.next, struct request, ipi_list);
                list_del_init(&rq->ipi_list);
                rq->q->softirq_done_fn(rq);
        }
}

#ifdef CONFIG_SMP
static void trigger_softirq(void *data)
{
        struct request *rq = data;
        unsigned long flags;
        struct list_head *list;

        local_irq_save(flags);
        list = this_cpu_ptr(&blk_cpu_done);
        list_add_tail(&rq->ipi_list, list);

        if (list->next == &rq->ipi_list)
                raise_softirq_irqoff(BLOCK_SOFTIRQ);

        local_irq_restore(flags);
}

/*
 * Setup and invoke a run of 'trigger_softirq' on the given cpu.
 */
static int raise_blk_irq(int cpu, struct request *rq)
{
        if (cpu_online(cpu)) {
                struct call_single_data *data = &rq->csd;

                data->func = trigger_softirq;
                data->info = rq;
                data->flags = 0;

                smp_call_function_single_async(cpu, data);
                return 0;
        }

        return 1;
}
#else /* CONFIG_SMP */
static int raise_blk_irq(int cpu, struct request *rq)
{
        return 1;
}
#endif

static int blk_cpu_notify(struct notifier_block *self, unsigned long action,
                          void *hcpu)
{
        /*
         * If a CPU goes away, splice its entries to the current CPU
         * and trigger a run of the softirq
         */
        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
                int cpu = (unsigned long) hcpu;

                local_irq_disable();
                list_splice_init(&per_cpu(blk_cpu_done, cpu),
                                 this_cpu_ptr(&blk_cpu_done));
                raise_softirq_irqoff(BLOCK_SOFTIRQ);
                local_irq_enable();
        }

        return NOTIFY_OK;
}

static struct notifier_block blk_cpu_notifier = {
        .notifier_call  = blk_cpu_notify,
};

void __blk_complete_request(struct request *req)
{
        int ccpu, cpu;
        struct request_queue *q = req->q;
        unsigned long flags;
        bool shared = false;

        BUG_ON(!q->softirq_done_fn);

        local_irq_save(flags);
        cpu = smp_processor_id();

        /*
         * Select completion CPU
         */
        if (req->cpu != -1) {
                ccpu = req->cpu;
                if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
                        shared = cpus_share_cache(cpu, ccpu);
        } else
                ccpu = cpu;

        /*
         * If current CPU and requested CPU share a cache, run the softirq on
         * the current CPU. One might concern this is just like
         * QUEUE_FLAG_SAME_FORCE, but actually not. blk_complete_request() is
         * running in interrupt handler, and currently I/O controller doesn't
         * support multiple interrupts, so current CPU is unique actually. This
         * avoids IPI sending from current CPU to the first CPU of a group.
         */
        if (ccpu == cpu || shared) {
                struct list_head *list;
do_local:
                list = this_cpu_ptr(&blk_cpu_done);
                list_add_tail(&req->ipi_list, list);

                /*
                 * if the list only contains our just added request,
                 * signal a raise of the softirq. If there are already
                 * entries there, someone already raised the irq but it
                 * hasn't run yet.
                 */
                if (list->next == &req->ipi_list)
                        raise_softirq_irqoff(BLOCK_SOFTIRQ);
        } else if (raise_blk_irq(ccpu, req))
                goto do_local;

        local_irq_restore(flags);
}

/**
 * blk_complete_request - end I/O on a request
 * @req:      the request being processed
 *
 * Description:
 *     Ends all I/O on a request. It does not handle partial completions,
 *     unless the driver actually implements this in its completion callback
 *     through requeueing. The actual completion happens out-of-order,
 *     through a softirq handler. The user must have registered a completion
 *     callback through blk_queue_softirq_done().
 **/
void blk_complete_request(struct request *req)
{
        if (unlikely(blk_should_fake_timeout(req->q)))
                return;
        if (!blk_mark_rq_complete(req))
                __blk_complete_request(req);
}
EXPORT_SYMBOL(blk_complete_request);

static __init int blk_softirq_init(void)
{
        int i;

        for_each_possible_cpu(i)
                INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));

        open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
        register_hotcpu_notifier(&blk_cpu_notifier);
        return 0;
}
subsys_initcall(blk_softirq_init);