From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Mon, 27 Jan 2020 19:00:36 +0000
Subject: [PATCH] virtio-fs: fix MSI-X nvectors calculation

The following MSI-X vectors are required:
 * VIRTIO Configuration Change
 * hiprio virtqueue
 * requests virtqueues

Fix the calculation to reserve enough MSI-X vectors.  Otherwise guest
drivers fall back to a sub-optional configuration where all virtqueues
share a single vector.

This change does not break live migration compatibility since
vhost-user-fs-pci devices are not migratable yet.

Reported-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20191209110759.35227-1-stefanha@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
(cherry picked from commit 366844f3d1329c6423dd752891a28ccb3ee8fddd)
---
 hw/virtio/vhost-user-fs-pci.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-user-fs-pci.c b/hw/virtio/vhost-user-fs-pci.c
index 933a3f265b..e3a649d4a6 100644
--- a/hw/virtio/vhost-user-fs-pci.c
+++ b/hw/virtio/vhost-user-fs-pci.c
@@ -40,7 +40,8 @@ static void vhost_user_fs_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
     DeviceState *vdev = DEVICE(&dev->vdev);
 
     if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
-        vpci_dev->nvectors = dev->vdev.conf.num_request_queues + 1;
+        /* Also reserve config change and hiprio queue vectors */
+        vpci_dev->nvectors = dev->vdev.conf.num_request_queues + 2;
     }
 
     qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));