virtio-scsi: introduce a constant for fixed virtqueues

The event and control virtqueues are always present, regardless of the
multi-queue configuration.  Define a constant so that virtqueue number
calculations are easier to read.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Message-Id: <20200818143348.310613-5-stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/scsi/vhost-user-scsi.c

@@ -114,7 +114,7 @@ static void vhost_user_scsi_realize(DeviceState *dev, Error **errp)
         goto free_virtio;
     }
 
-    vsc->dev.nvqs = 2 + vs->conf.num_queues;
+    vsc->dev.nvqs = VIRTIO_SCSI_VQ_NUM_FIXED + vs->conf.num_queues;
     vsc->dev.vqs = g_new0(struct vhost_virtqueue, vsc->dev.nvqs);
     vsc->dev.vq_index = 0;
     vsc->dev.backend_features = 0;

hw/scsi/virtio-scsi.c

@@ -191,7 +191,7 @@ static void virtio_scsi_save_request(QEMUFile *f, SCSIRequest *sreq)
     VirtIOSCSIReq *req = sreq->hba_private;
     VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(req->dev);
     VirtIODevice *vdev = VIRTIO_DEVICE(req->dev);
-    uint32_t n = virtio_get_queue_index(req->vq) - 2;
+    uint32_t n = virtio_get_queue_index(req->vq) - VIRTIO_SCSI_VQ_NUM_FIXED;
 
     assert(n < vs->conf.num_queues);
     qemu_put_be32s(f, &n);
@@ -892,10 +892,11 @@ void virtio_scsi_common_realize(DeviceState *dev,
                 sizeof(VirtIOSCSIConfig));
 
     if (s->conf.num_queues == 0 ||
-            s->conf.num_queues > VIRTIO_QUEUE_MAX - 2) {
+            s->conf.num_queues > VIRTIO_QUEUE_MAX - VIRTIO_SCSI_VQ_NUM_FIXED) {
         error_setg(errp, "Invalid number of queues (= %" PRIu32 "), "
                          "must be a positive integer less than %d.",
-                   s->conf.num_queues, VIRTIO_QUEUE_MAX - 2);
+                   s->conf.num_queues,
+                   VIRTIO_QUEUE_MAX - VIRTIO_SCSI_VQ_NUM_FIXED);
         virtio_cleanup(vdev);
         return;
     }

hw/virtio/vhost-scsi-pci.c

@@ -50,7 +50,8 @@ static void vhost_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
     VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(vdev);
 
     if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
-        vpci_dev->nvectors = vs->conf.num_queues + 3;
+        vpci_dev->nvectors = vs->conf.num_queues +
+                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
     }
 
     qdev_realize(vdev, BUS(&vpci_dev->bus), errp);

hw/virtio/vhost-user-scsi-pci.c

@@ -56,7 +56,8 @@ static void vhost_user_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
     VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(vdev);
 
     if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
-        vpci_dev->nvectors = vs->conf.num_queues + 3;
+        vpci_dev->nvectors = vs->conf.num_queues +
+                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
     }
 
     qdev_realize(vdev, BUS(&vpci_dev->bus), errp);

hw/virtio/virtio-scsi-pci.c

@@ -51,7 +51,8 @@ static void virtio_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
     char *bus_name;
 
     if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
-        vpci_dev->nvectors = vs->conf.num_queues + 3;
+        vpci_dev->nvectors = vs->conf.num_queues +
+                             VIRTIO_SCSI_VQ_NUM_FIXED + 1;
     }
 
     /*

include/hw/virtio/virtio-scsi.h

@@ -36,6 +36,9 @@
 #define VIRTIO_SCSI_MAX_TARGET  255
 #define VIRTIO_SCSI_MAX_LUN     16383
 
+/* Number of virtqueues that are always present */
+#define VIRTIO_SCSI_VQ_NUM_FIXED    2
+
 typedef struct virtio_scsi_cmd_req VirtIOSCSICmdReq;
 typedef struct virtio_scsi_cmd_resp VirtIOSCSICmdResp;
 typedef struct virtio_scsi_ctrl_tmf_req VirtIOSCSICtrlTMFReq;