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/* Virtio balloon implementation, inspired by Dor Loar and Marcelo
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* Tosatti's implementations.
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* Copyright 2008 Rusty Russell IBM Corporation
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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#include <linux/virtio.h>
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#include <linux/virtio_balloon.h>
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#include <linux/swap.h>
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#include <linux/kthread.h>
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#include <linux/freezer.h>
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#include <linux/delay.h>
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#include <linux/slab.h>
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#include <linux/module.h>
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struct virtio_device *vdev;
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struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
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/* Where the ballooning thread waits for config to change. */
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wait_queue_head_t config_change;
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/* The thread servicing the balloon. */
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struct task_struct *thread;
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/* Waiting for host to ack the pages we released. */
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struct completion acked;
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/* The pages we've told the Host we're not using. */
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unsigned int num_pages;
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struct list_head pages;
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/* The array of pfns we tell the Host about. */
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unsigned int num_pfns;
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/* Memory statistics */
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int need_stats_update;
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struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
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static struct virtio_device_id id_table[] = {
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{ VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
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static u32 page_to_balloon_pfn(struct page *page)
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unsigned long pfn = page_to_pfn(page);
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BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
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/* Convert pfn from Linux page size to balloon page size. */
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return pfn >> (PAGE_SHIFT - VIRTIO_BALLOON_PFN_SHIFT);
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static void balloon_ack(struct virtqueue *vq)
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struct virtio_balloon *vb;
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vb = virtqueue_get_buf(vq, &len);
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static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
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struct scatterlist sg;
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sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
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init_completion(&vb->acked);
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/* We should always be able to add one buffer to an empty queue. */
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if (virtqueue_add_buf(vq, &sg, 1, 0, vb) < 0)
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/* When host has read buffer, this completes via balloon_ack */
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wait_for_completion(&vb->acked);
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static void fill_balloon(struct virtio_balloon *vb, size_t num)
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/* We can only do one array worth at a time. */
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num = min(num, ARRAY_SIZE(vb->pfns));
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for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
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struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
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__GFP_NOMEMALLOC | __GFP_NOWARN);
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if (printk_ratelimit())
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dev_printk(KERN_INFO, &vb->vdev->dev,
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"Out of puff! Can't get %zu pages\n",
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/* Sleep for at least 1/5 of a second before retry. */
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vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
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list_add(&page->lru, &vb->pages);
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/* Didn't get any? Oh well. */
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if (vb->num_pfns == 0)
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tell_host(vb, vb->inflate_vq);
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static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
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for (i = 0; i < num; i++) {
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__free_page(pfn_to_page(pfns[i]));
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static void leak_balloon(struct virtio_balloon *vb, size_t num)
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/* We can only do one array worth at a time. */
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num = min(num, ARRAY_SIZE(vb->pfns));
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for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
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page = list_first_entry(&vb->pages, struct page, lru);
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list_del(&page->lru);
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vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
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* virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
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* is true, we *have* to do it in this order
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tell_host(vb, vb->deflate_vq);
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release_pages_by_pfn(vb->pfns, vb->num_pfns);
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static inline void update_stat(struct virtio_balloon *vb, int idx,
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BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
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vb->stats[idx].tag = tag;
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vb->stats[idx].val = val;
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#define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
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static void update_balloon_stats(struct virtio_balloon *vb)
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unsigned long events[NR_VM_EVENT_ITEMS];
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all_vm_events(events);
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update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
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pages_to_bytes(events[PSWPIN]));
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update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
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pages_to_bytes(events[PSWPOUT]));
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update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
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update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
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update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
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pages_to_bytes(i.freeram));
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update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
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pages_to_bytes(i.totalram));
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* While most virtqueues communicate guest-initiated requests to the hypervisor,
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* the stats queue operates in reverse. The driver initializes the virtqueue
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* with a single buffer. From that point forward, all conversations consist of
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* a hypervisor request (a call to this function) which directs us to refill
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* the virtqueue with a fresh stats buffer. Since stats collection can sleep,
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* we notify our kthread which does the actual work via stats_handle_request().
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static void stats_request(struct virtqueue *vq)
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struct virtio_balloon *vb;
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vb = virtqueue_get_buf(vq, &len);
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vb->need_stats_update = 1;
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wake_up(&vb->config_change);
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static void stats_handle_request(struct virtio_balloon *vb)
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struct virtqueue *vq;
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struct scatterlist sg;
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vb->need_stats_update = 0;
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update_balloon_stats(vb);
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sg_init_one(&sg, vb->stats, sizeof(vb->stats));
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if (virtqueue_add_buf(vq, &sg, 1, 0, vb) < 0)
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static void virtballoon_changed(struct virtio_device *vdev)
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struct virtio_balloon *vb = vdev->priv;
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wake_up(&vb->config_change);
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static inline s64 towards_target(struct virtio_balloon *vb)
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vb->vdev->config->get(vb->vdev,
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offsetof(struct virtio_balloon_config, num_pages),
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return (s64)v - vb->num_pages;
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static void update_balloon_size(struct virtio_balloon *vb)
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__le32 actual = cpu_to_le32(vb->num_pages);
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vb->vdev->config->set(vb->vdev,
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offsetof(struct virtio_balloon_config, actual),
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&actual, sizeof(actual));
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static int balloon(void *_vballoon)
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struct virtio_balloon *vb = _vballoon;
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while (!kthread_should_stop()) {
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wait_event_interruptible(vb->config_change,
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(diff = towards_target(vb)) != 0
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|| vb->need_stats_update
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|| kthread_should_stop()
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|| freezing(current));
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if (vb->need_stats_update)
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stats_handle_request(vb);
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fill_balloon(vb, diff);
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leak_balloon(vb, -diff);
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update_balloon_size(vb);
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static int virtballoon_probe(struct virtio_device *vdev)
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struct virtio_balloon *vb;
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struct virtqueue *vqs[3];
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vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
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const char *names[] = { "inflate", "deflate", "stats" };
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vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
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INIT_LIST_HEAD(&vb->pages);
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init_waitqueue_head(&vb->config_change);
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vb->need_stats_update = 0;
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/* We expect two virtqueues: inflate and deflate,
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* and optionally stat. */
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nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
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err = vdev->config->find_vqs(vdev, nvqs, vqs, callbacks, names);
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vb->inflate_vq = vqs[0];
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vb->deflate_vq = vqs[1];
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if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
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struct scatterlist sg;
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vb->stats_vq = vqs[2];
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* Prime this virtqueue with one buffer so the hypervisor can
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* use it to signal us later.
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sg_init_one(&sg, vb->stats, sizeof vb->stats);
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if (virtqueue_add_buf(vb->stats_vq, &sg, 1, 0, vb) < 0)
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virtqueue_kick(vb->stats_vq);
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vb->thread = kthread_run(balloon, vb, "vballoon");
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if (IS_ERR(vb->thread)) {
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err = PTR_ERR(vb->thread);
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vdev->config->del_vqs(vdev);
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static void __devexit virtballoon_remove(struct virtio_device *vdev)
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struct virtio_balloon *vb = vdev->priv;
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kthread_stop(vb->thread);
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/* There might be pages left in the balloon: free them. */
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while (vb->num_pages)
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leak_balloon(vb, vb->num_pages);
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/* Now we reset the device so we can clean up the queues. */
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vdev->config->reset(vdev);
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vdev->config->del_vqs(vdev);
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static unsigned int features[] = {
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VIRTIO_BALLOON_F_MUST_TELL_HOST,
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VIRTIO_BALLOON_F_STATS_VQ,
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static struct virtio_driver virtio_balloon_driver = {
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.feature_table = features,
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.feature_table_size = ARRAY_SIZE(features),
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.driver.name = KBUILD_MODNAME,
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.driver.owner = THIS_MODULE,
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.id_table = id_table,
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.probe = virtballoon_probe,
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.remove = __devexit_p(virtballoon_remove),
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.config_changed = virtballoon_changed,
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static int __init init(void)
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return register_virtio_driver(&virtio_balloon_driver);
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static void __exit fini(void)
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unregister_virtio_driver(&virtio_balloon_driver);
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MODULE_DEVICE_TABLE(virtio, id_table);
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MODULE_DESCRIPTION("Virtio balloon driver");
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MODULE_LICENSE("GPL");