/* Virtio balloon implementation, inspired by Dor Loar and Marcelo
 * Tosatti's implementations.
 *
 *  Copyright 2008 Rusty Russell IBM Corporation
 *
 *  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.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
//#define DEBUG
#include <linux/virtio.h>
#include <linux/virtio_balloon.h>
#include <linux/swap.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/delay.h>

struct virtio_balloon
{
        struct virtio_device *vdev;
        struct virtqueue *inflate_vq, *deflate_vq;

        /* Where the ballooning thread waits for config to change. */
        wait_queue_head_t config_change;

        /* The thread servicing the balloon. */
        struct task_struct *thread;

        /* Waiting for host to ack the pages we released. */
        struct completion acked;

        /* Do we have to tell Host *before* we reuse pages? */
        bool tell_host_first;

        /* The pages we've told the Host we're not using. */
        unsigned int num_pages;
        struct list_head pages;

        /* The array of pfns we tell the Host about. */
        unsigned int num_pfns;
        u32 pfns[256];
};

static struct virtio_device_id id_table[] = {
        { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
        { 0 },
};

static u32 page_to_balloon_pfn(struct page *page)
{
        unsigned long pfn = page_to_pfn(page);

        BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
        /* Convert pfn from Linux page size to balloon page size. */
        return pfn >> (PAGE_SHIFT - VIRTIO_BALLOON_PFN_SHIFT);
}

static void balloon_ack(struct virtqueue *vq)
{
        struct virtio_balloon *vb;
        unsigned int len;

        vb = vq->vq_ops->get_buf(vq, &len);
        if (vb)
                complete(&vb->acked);
}

static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
{
        struct scatterlist sg;

        sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);

        init_completion(&vb->acked);

        /* We should always be able to add one buffer to an empty queue. */
        if (vq->vq_ops->add_buf(vq, &sg, 1, 0, vb) < 0)
                BUG();
        vq->vq_ops->kick(vq);

        /* When host has read buffer, this completes via balloon_ack */
        wait_for_completion(&vb->acked);
}

static void fill_balloon(struct virtio_balloon *vb, size_t num)
{
        /* We can only do one array worth at a time. */
        num = min(num, ARRAY_SIZE(vb->pfns));

        for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
                struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY);
                if (!page) {
                        if (printk_ratelimit())
                                dev_printk(KERN_INFO, &vb->vdev->dev,
                                           "Out of puff! Can't get %zu pages\n",
                                           num);
                        /* Sleep for at least 1/5 of a second before retry. */
                        msleep(200);
                        break;
                }
                vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
                totalram_pages--;
                vb->num_pages++;
                list_add(&page->lru, &vb->pages);
        }

        /* Didn't get any?  Oh well. */
        if (vb->num_pfns == 0)
                return;

        tell_host(vb, vb->inflate_vq);
}

static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
{
        unsigned int i;

        for (i = 0; i < num; i++) {
                __free_page(pfn_to_page(pfns[i]));
                totalram_pages++;
        }
}

static void leak_balloon(struct virtio_balloon *vb, size_t num)
{
        struct page *page;

        /* We can only do one array worth at a time. */
        num = min(num, ARRAY_SIZE(vb->pfns));

        for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
                page = list_first_entry(&vb->pages, struct page, lru);
                list_del(&page->lru);
                vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
                vb->num_pages--;
        }

        if (vb->tell_host_first) {
                tell_host(vb, vb->deflate_vq);
                release_pages_by_pfn(vb->pfns, vb->num_pfns);
        } else {
                release_pages_by_pfn(vb->pfns, vb->num_pfns);
                tell_host(vb, vb->deflate_vq);
        }
}

static void virtballoon_changed(struct virtio_device *vdev)
{
        struct virtio_balloon *vb = vdev->priv;

        wake_up(&vb->config_change);
}

static inline s64 towards_target(struct virtio_balloon *vb)
{
        u32 v;
        vb->vdev->config->get(vb->vdev,
                              offsetof(struct virtio_balloon_config, num_pages),
                              &v, sizeof(v));
        return (s64)v - vb->num_pages;
}

static void update_balloon_size(struct virtio_balloon *vb)
{
        __le32 actual = cpu_to_le32(vb->num_pages);

        vb->vdev->config->set(vb->vdev,
                              offsetof(struct virtio_balloon_config, actual),
                              &actual, sizeof(actual));
}

static int balloon(void *_vballoon)
{
        struct virtio_balloon *vb = _vballoon;

        set_freezable();
        while (!kthread_should_stop()) {
                s64 diff;

                try_to_freeze();
                wait_event_interruptible(vb->config_change,
                                         (diff = towards_target(vb)) != 0
                                         || kthread_should_stop()
                                         || freezing(current));
                if (diff > 0)
                        fill_balloon(vb, diff);
                else if (diff < 0)
                        leak_balloon(vb, -diff);
                update_balloon_size(vb);
        }
        return 0;
}

static int virtballoon_probe(struct virtio_device *vdev)
{
        struct virtio_balloon *vb;
        struct virtqueue *vqs[2];
        vq_callback_t *callbacks[] = { balloon_ack, balloon_ack };
        const char *names[] = { "inflate", "deflate" };
        int err;

        vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
        if (!vb) {
                err = -ENOMEM;
                goto out;
        }

        INIT_LIST_HEAD(&vb->pages);
        vb->num_pages = 0;
        init_waitqueue_head(&vb->config_change);
        vb->vdev = vdev;

        /* We expect two virtqueues. */
        err = vdev->config->find_vqs(vdev, 2, vqs, callbacks, names);
        if (err)
                goto out_free_vb;

        vb->inflate_vq = vqs[0];
        vb->deflate_vq = vqs[1];

        vb->thread = kthread_run(balloon, vb, "vballoon");
        if (IS_ERR(vb->thread)) {
                err = PTR_ERR(vb->thread);
                goto out_del_vqs;
        }

        vb->tell_host_first
                = virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);

        return 0;

out_del_vqs:
        vdev->config->del_vqs(vdev);
out_free_vb:
        kfree(vb);
out:
        return err;
}

static void __devexit virtballoon_remove(struct virtio_device *vdev)
{
        struct virtio_balloon *vb = vdev->priv;

        kthread_stop(vb->thread);

        /* There might be pages left in the balloon: free them. */
        while (vb->num_pages)
                leak_balloon(vb, vb->num_pages);

        /* Now we reset the device so we can clean up the queues. */
        vdev->config->reset(vdev);

        vdev->config->del_vqs(vdev);
        kfree(vb);
}

static unsigned int features[] = { VIRTIO_BALLOON_F_MUST_TELL_HOST };

static struct virtio_driver virtio_balloon = {
        .feature_table = features,
        .feature_table_size = ARRAY_SIZE(features),
        .driver.name =  KBUILD_MODNAME,
        .driver.owner = THIS_MODULE,
        .id_table =     id_table,
        .probe =        virtballoon_probe,
        .remove =       __devexit_p(virtballoon_remove),
        .config_changed = virtballoon_changed,
};

static int __init init(void)
{
        return register_virtio_driver(&virtio_balloon);
}

static void __exit fini(void)
{
        unregister_virtio_driver(&virtio_balloon);
}
module_init(init);
module_exit(fini);

MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio balloon driver");
MODULE_LICENSE("GPL");