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From f7d6a76475d29e0edb5456e62492117b87f4bc41 Mon Sep 17 00:00:00 2001
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From: Ladi Prosek <lprosek@redhat.com>
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Date: Thu, 10 Nov 2016 23:00:50 +0100
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Subject: [PATCH 7/8] virtio: add virtqueue_rewind()
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RH-Author: Ladi Prosek <lprosek@redhat.com>
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Message-id: <1478797251-10302-1-git-send-email-lprosek@redhat.com>
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Patchwork-id: 72818
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O-Subject: [PATCH v2 7/6] virtio: add virtqueue_rewind()
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Bugzilla: 1393484
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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From: Stefan Hajnoczi <stefanha@redhat.com>
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virtqueue_discard() requires a VirtQueueElement but virtio-balloon does
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not migrate its in-use element. Introduce a new function that is
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similar to virtqueue_discard() but doesn't require a VirtQueueElement.
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This will allow virtio-balloon to access element again after migration
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with the usual proviso that the guest may have modified the vring since
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last time.
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Cc: Michael S. Tsirkin <mst@redhat.com>
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Cc: Roman Kagan <rkagan@virtuozzo.com>
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Cc: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Ladi Prosek <lprosek@redhat.com>
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Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
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Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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(cherry picked from commit 297a75e6c55d91db2704a3d6e4029d99c7df51fd)
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Signed-off-by: Ladi Prosek <lprosek@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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hw/virtio/virtio.c | 22 ++++++++++++++++++++++
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include/hw/virtio/virtio.h | 1 +
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2 files changed, 23 insertions(+)
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diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
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index cdb21b1..fe6b032 100644
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--- a/hw/virtio/virtio.c
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+++ b/hw/virtio/virtio.c
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@@ -259,6 +259,28 @@ void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem,
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virtqueue_unmap_sg(vq, elem, len);
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}
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+/* virtqueue_rewind:
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+ * @vq: The #VirtQueue
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+ * @num: Number of elements to push back
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+ *
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+ * Pretend that elements weren't popped from the virtqueue. The next
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+ * virtqueue_pop() will refetch the oldest element.
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+ *
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+ * Use virtqueue_discard() instead if you have a VirtQueueElement.
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+ *
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+ * Returns: true on success, false if @num is greater than the number of in use
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+ * elements.
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+ */
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+bool virtqueue_rewind(VirtQueue *vq, unsigned int num)
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+{
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+ if (num > vq->inuse) {
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+ return false;
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+ }
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+ vq->last_avail_idx -= num;
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+ vq->inuse -= num;
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+ return true;
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+}
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+
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void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
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unsigned int len, unsigned int idx)
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{
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diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
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index de32425..d9bfe4c 100644
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--- a/include/hw/virtio/virtio.h
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+++ b/include/hw/virtio/virtio.h
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@@ -167,6 +167,7 @@ void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem,
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void virtqueue_flush(VirtQueue *vq, unsigned int count);
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void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem,
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unsigned int len);
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+bool virtqueue_rewind(VirtQueue *vq, unsigned int num);
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void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
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unsigned int len, unsigned int idx);
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--
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1.8.3.1
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