/*
 * VFIO generic eventfd code for IRQFD support.
 * Derived from drivers/vfio/pci/vfio_pci_intrs.c
 *
 * Copyright (C) 2012 Red Hat, Inc.  All rights reserved.
 *     Author: Alex Williamson <alex.williamson@redhat.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/vfio.h>
#include <linux/eventfd.h>
#include <linux/file.h>
#include <linux/module.h>
#include <linux/slab.h>

#define DRIVER_VERSION  "0.1"
#define DRIVER_AUTHOR   "Alex Williamson <alex.williamson@redhat.com>"
#define DRIVER_DESC     "IRQFD support for VFIO bus drivers"

static struct workqueue_struct *vfio_irqfd_cleanup_wq;
static DEFINE_SPINLOCK(virqfd_lock);

static int __init vfio_virqfd_init(void)
{
        vfio_irqfd_cleanup_wq =
                create_singlethread_workqueue("vfio-irqfd-cleanup");
        if (!vfio_irqfd_cleanup_wq)
                return -ENOMEM;

        return 0;
}

static void __exit vfio_virqfd_exit(void)
{
        destroy_workqueue(vfio_irqfd_cleanup_wq);
}

static void virqfd_deactivate(struct virqfd *virqfd)
{
        queue_work(vfio_irqfd_cleanup_wq, &virqfd->shutdown);
}

static int virqfd_wakeup(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
{
        struct virqfd *virqfd = container_of(wait, struct virqfd, wait);
        __poll_t flags = key_to_poll(key);

        if (flags & EPOLLIN) {
                /* An event has been signaled, call function */
                if ((!virqfd->handler ||
                     virqfd->handler(virqfd->opaque, virqfd->data)) &&
                    virqfd->thread)
                        schedule_work(&virqfd->inject);
        }

        if (flags & EPOLLHUP) {
                unsigned long flags;
                spin_lock_irqsave(&virqfd_lock, flags);

                /*
                 * The eventfd is closing, if the virqfd has not yet been
                 * queued for release, as determined by testing whether the
                 * virqfd pointer to it is still valid, queue it now.  As
                 * with kvm irqfds, we know we won't race against the virqfd
                 * going away because we hold the lock to get here.
                 */
                if (*(virqfd->pvirqfd) == virqfd) {
                        *(virqfd->pvirqfd) = NULL;
                        virqfd_deactivate(virqfd);
                }

                spin_unlock_irqrestore(&virqfd_lock, flags);
        }

        return 0;
}

static void virqfd_ptable_queue_proc(struct file *file,
                                     wait_queue_head_t *wqh, poll_table *pt)
{
        struct virqfd *virqfd = container_of(pt, struct virqfd, pt);
        add_wait_queue(wqh, &virqfd->wait);
}

static void virqfd_shutdown(struct work_struct *work)
{
        struct virqfd *virqfd = container_of(work, struct virqfd, shutdown);
        u64 cnt;

        eventfd_ctx_remove_wait_queue(virqfd->eventfd, &virqfd->wait, &cnt);
        flush_work(&virqfd->inject);
        eventfd_ctx_put(virqfd->eventfd);

        kfree(virqfd);
}

static void virqfd_inject(struct work_struct *work)
{
        struct virqfd *virqfd = container_of(work, struct virqfd, inject);
        if (virqfd->thread)
                virqfd->thread(virqfd->opaque, virqfd->data);
}

int vfio_virqfd_enable(void *opaque,
                       int (*handler)(void *, void *),
                       void (*thread)(void *, void *),
                       void *data, struct virqfd **pvirqfd, int fd)
{
        struct fd irqfd;
        struct eventfd_ctx *ctx;
        struct virqfd *virqfd;
        int ret = 0;
        __poll_t events;

        virqfd = kzalloc(sizeof(*virqfd), GFP_KERNEL);
        if (!virqfd)
                return -ENOMEM;

        virqfd->pvirqfd = pvirqfd;
        virqfd->opaque = opaque;
        virqfd->handler = handler;
        virqfd->thread = thread;
        virqfd->data = data;

        INIT_WORK(&virqfd->shutdown, virqfd_shutdown);
        INIT_WORK(&virqfd->inject, virqfd_inject);

        irqfd = fdget(fd);
        if (!irqfd.file) {
                ret = -EBADF;
                goto err_fd;
        }

        ctx = eventfd_ctx_fileget(irqfd.file);
        if (IS_ERR(ctx)) {
                ret = PTR_ERR(ctx);
                goto err_ctx;
        }

        virqfd->eventfd = ctx;

        /*
         * virqfds can be released by closing the eventfd or directly
         * through ioctl.  These are both done through a workqueue, so
         * we update the pointer to the virqfd under lock to avoid
         * pushing multiple jobs to release the same virqfd.
         */
        spin_lock_irq(&virqfd_lock);

        if (*pvirqfd) {
                spin_unlock_irq(&virqfd_lock);
                ret = -EBUSY;
                goto err_busy;
        }
        *pvirqfd = virqfd;

        spin_unlock_irq(&virqfd_lock);

        /*
         * Install our own custom wake-up handling so we are notified via
         * a callback whenever someone signals the underlying eventfd.
         */
        init_waitqueue_func_entry(&virqfd->wait, virqfd_wakeup);
        init_poll_funcptr(&virqfd->pt, virqfd_ptable_queue_proc);

        events = irqfd.file->f_op->poll(irqfd.file, &virqfd->pt);

        /*
         * Check if there was an event already pending on the eventfd
         * before we registered and trigger it as if we didn't miss it.
         */
        if (events & EPOLLIN) {
                if ((!handler || handler(opaque, data)) && thread)
                        schedule_work(&virqfd->inject);
        }

        /*
         * Do not drop the file until the irqfd is fully initialized,
         * otherwise we might race against the EPOLLHUP.
         */
        fdput(irqfd);

        return 0;
err_busy:
        eventfd_ctx_put(ctx);
err_ctx:
        fdput(irqfd);
err_fd:
        kfree(virqfd);

        return ret;
}
EXPORT_SYMBOL_GPL(vfio_virqfd_enable);

void vfio_virqfd_disable(struct virqfd **pvirqfd)
{
        unsigned long flags;

        spin_lock_irqsave(&virqfd_lock, flags);

        if (*pvirqfd) {
                virqfd_deactivate(*pvirqfd);
                *pvirqfd = NULL;
        }

        spin_unlock_irqrestore(&virqfd_lock, flags);

        /*
         * Block until we know all outstanding shutdown jobs have completed.
         * Even if we don't queue the job, flush the wq to be sure it's
         * been released.
         */
        flush_workqueue(vfio_irqfd_cleanup_wq);
}
EXPORT_SYMBOL_GPL(vfio_virqfd_disable);

module_init(vfio_virqfd_init);
module_exit(vfio_virqfd_exit);

MODULE_VERSION(DRIVER_VERSION);
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR(DRIVER_AUTHOR);
MODULE_DESCRIPTION(DRIVER_DESC);