[RFC-v2 4/6] virtio-scsi: Add start/stop functionality for vhost-scsi

["Nicholas A. Bellinger" <nab@linux-iscsi.org>]

From: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

This patch starts and stops vhost as the virtio device transitions
through its status phases.  Vhost can only be started once the guest
reports its driver has successfully initialized, which means the
virtqueues have been set up by the guest.

v2: - Squash virtio-scsi: use the vhost-scsi host device from stefan (nab)
    - Fix up virtio_scsi_properties[] conflict w/ upstream qemu (nab)
    - Drop usage of to_virtio_scsi() in virtio_scsi_set_status()
      (reported by paolo)
    - Use modern VirtIOSCSIConf define in virtio-scsi.h (reported by paolo)
    - Use s->conf->vhost_scsi instead of proxyconf->vhost_scsi in
      virtio_scsi_init() (reported by paolo)
    - Only register QEMU SCSI bus is vhost-scsi is not active (reported
      by paolo)

Cc: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Cc: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
---
 hw/virtio-pci.c  |    1 +
 hw/virtio-scsi.c |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
 hw/virtio-scsi.h |    1 +
 3 files changed, 50 insertions(+), 0 deletions(-)

diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index 125eded..b29fc3b 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -1036,6 +1036,7 @@ static void virtio_scsi_exit_pci(PCIDevice *pci_dev)
 }
 
 static Property virtio_scsi_properties[] = {
+    DEFINE_PROP_VHOST_SCSI("vhost-scsi", VirtIOPCIProxy, scsi.vhost_scsi),
     DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags, VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
     DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, DEV_NVECTORS_UNSPECIFIED),
     DEFINE_VIRTIO_SCSI_PROPERTIES(VirtIOPCIProxy, host_features, scsi),
diff --git a/hw/virtio-scsi.c b/hw/virtio-scsi.c
index 5f737ac..8130956 100644
--- a/hw/virtio-scsi.c
+++ b/hw/virtio-scsi.c
@@ -13,9 +13,13 @@
  *
  */
 
+#include "qemu-common.h"
+#include "qemu-error.h"
+#include "vhost-scsi.h"
 #include "virtio-scsi.h"
 #include <hw/scsi.h>
 #include <hw/scsi-defs.h>
+#include "vhost.h"
 
 #define VIRTIO_SCSI_VQ_SIZE     128
 #define VIRTIO_SCSI_CDB_SIZE    32
@@ -147,6 +151,9 @@ typedef struct {
     VirtQueue *ctrl_vq;
     VirtQueue *event_vq;
     VirtQueue *cmd_vqs[0];
+
+    bool vhost_started;
+    VHostSCSI *vhost_scsi;
 } VirtIOSCSI;
 
 typedef struct VirtIOSCSIReq {
@@ -699,6 +706,38 @@ static struct SCSIBusInfo virtio_scsi_scsi_info = {
     .load_request = virtio_scsi_load_request,
 };
 
+static bool virtio_scsi_started(VirtIOSCSI *s, uint8_t val)
+{
+    return (val & VIRTIO_CONFIG_S_DRIVER_OK) && s->vdev.vm_running;
+}
+
+static void virtio_scsi_set_status(VirtIODevice *vdev, uint8_t val)
+{
+    VirtIOSCSI *s = (VirtIOSCSI *)vdev;
+    bool start = virtio_scsi_started(s, val);
+
+    if (s->vhost_started == start) {
+        return;
+    }
+
+    if (start) {
+        int ret;
+
+        ret = vhost_scsi_start(s->vhost_scsi, vdev);
+        if (ret < 0) {
+            error_report("virtio-scsi: unable to start vhost: %s\n",
+                         strerror(-ret));
+
+            /* There is no userspace virtio-scsi fallback so exit */
+            exit(1);
+        }
+    } else {
+        vhost_scsi_stop(s->vhost_scsi, vdev);
+    }
+
+    s->vhost_started = start;
+}
+
 VirtIODevice *virtio_scsi_init(DeviceState *dev, VirtIOSCSIConf *proxyconf)
 {
     VirtIOSCSI *s;
@@ -712,12 +751,17 @@ VirtIODevice *virtio_scsi_init(DeviceState *dev, VirtIOSCSIConf *proxyconf)
 
     s->qdev = dev;
     s->conf = proxyconf;
+    s->vhost_started = false;
+    s->vhost_scsi = s->conf->vhost_scsi;
 
     /* TODO set up vdev function pointers */
     s->vdev.get_config = virtio_scsi_get_config;
     s->vdev.set_config = virtio_scsi_set_config;
     s->vdev.get_features = virtio_scsi_get_features;
     s->vdev.reset = virtio_scsi_reset;
+    if (s->vhost_scsi) {
+        s->vdev.set_status = virtio_scsi_set_status;
+    }
 
     s->ctrl_vq = virtio_add_queue(&s->vdev, VIRTIO_SCSI_VQ_SIZE,
                                    virtio_scsi_handle_ctrl);
@@ -743,5 +787,9 @@ void virtio_scsi_exit(VirtIODevice *vdev)
 {
     VirtIOSCSI *s = (VirtIOSCSI *)vdev;
     unregister_savevm(s->qdev, "virtio-scsi", s);
+
+    /* This will stop vhost backend if appropriate. */
+    virtio_scsi_set_status(vdev, 0);
+
     virtio_cleanup(vdev);
 }
diff --git a/hw/virtio-scsi.h b/hw/virtio-scsi.h
index 4bc889d..74e9422 100644
--- a/hw/virtio-scsi.h
+++ b/hw/virtio-scsi.h
@@ -22,6 +22,7 @@
 #define VIRTIO_ID_SCSI  8
 
 struct VirtIOSCSIConf {
+    VHostSCSI *vhost_scsi;
     uint32_t num_queues;
     uint32_t max_sectors;
     uint32_t cmd_per_lun;
-- 
1.7.2.5