[Xen-changelog] [qemu-xen stable-4.10] virtio: Add queue interface to restore avail index from vring used index

[patchbot@xxxxxxx]

commit 059422ddbc9e3b7fbe54a6d87b9ac0b329bb16b9
Author:     Maxime Coquelin <maxime.coquelin@xxxxxxxxxx>
AuthorDate: Thu Nov 16 19:48:34 2017 +0100
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Wed Dec 6 09:55:16 2017 -0600

    virtio: Add queue interface to restore avail index from vring used index
    
    In case of backend crash, it is not possible to restore internal
    avail index from the backend value as vhost_get_vring_base
    callback fails.
    
    This patch provides a new interface to restore internal avail index
    from the vring used index, as done by some vhost-user backend on
    reconnection.
    
    Signed-off-by: Maxime Coquelin <maxime.coquelin@xxxxxxxxxx>
    Reviewed-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
    Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
    (cherry picked from commit 2d4ba6cc741df15df6fbb4feaa706a02e103083a)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 hw/virtio/virtio.c         | 10 ++++++++++
 include/hw/virtio/virtio.h |  1 +
 2 files changed, 11 insertions(+)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 464947f..15cf602 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2311,6 +2311,16 @@ void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, 
int n, uint16_t idx)
     vdev->vq[n].shadow_avail_idx = idx;
 }
 
+void virtio_queue_restore_last_avail_idx(VirtIODevice *vdev, int n)
+{
+    rcu_read_lock();
+    if (vdev->vq[n].vring.desc) {
+        vdev->vq[n].last_avail_idx = vring_used_idx(&vdev->vq[n]);
+        vdev->vq[n].shadow_avail_idx = vdev->vq[n].last_avail_idx;
+    }
+    rcu_read_unlock();
+}
+
 void virtio_queue_update_used_idx(VirtIODevice *vdev, int n)
 {
     rcu_read_lock();
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 80c45c3..3d5c84e 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -272,6 +272,7 @@ hwaddr virtio_queue_get_avail_size(VirtIODevice *vdev, int 
n);
 hwaddr virtio_queue_get_used_size(VirtIODevice *vdev, int n);
 uint16_t virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n);
 void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, uint16_t idx);
+void virtio_queue_restore_last_avail_idx(VirtIODevice *vdev, int n);
 void virtio_queue_invalidate_signalled_used(VirtIODevice *vdev, int n);
 void virtio_queue_update_used_idx(VirtIODevice *vdev, int n);
 VirtQueue *virtio_get_queue(VirtIODevice *vdev, int n);
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#stable-4.10

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