hw/virtio: move vhd->started check into helper and add FIXME

The `started` field is manipulated internally within the vhost code
except for one place, vhost-user-blk via f5b22d06fb (vhost: recheck
dev state in the vhost_migration_log routine). Mark that as a FIXME
because it introduces a potential race. I think the referenced fix
should be tracking its state locally.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220802095010.3330793-12-alex.bennee@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Raphael Norwitz <raphael.norwittz@nutanix.com>

hw/block/vhost-user-blk.c

@@ -229,7 +229,7 @@ static void vhost_user_blk_set_status(VirtIODevice *vdev, uint8_t status)
         return;
     }
 
-    if (s->dev.started == should_start) {
+    if (vhost_dev_is_started(&s->dev) == should_start) {
         return;
     }
 
@@ -286,7 +286,7 @@ static void vhost_user_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
         return;
     }
 
-    if (s->dev.started) {
+    if (vhost_dev_is_started(&s->dev)) {
         return;
     }
 
@@ -415,6 +415,12 @@ static void vhost_user_blk_event(void *opaque, QEMUChrEvent event)
              * the vhost migration code. If disconnect was caught there is an
              * option for the general vhost code to get the dev state without
              * knowing its type (in this case vhost-user).
+             *
+             * FIXME: this is sketchy to be reaching into vhost_dev
+             * now because we are forcing something that implies we
+             * have executed vhost_dev_stop() but that won't happen
+             * until vhost_user_blk_stop() gets called from the bh.
+             * Really this state check should be tracked locally.
              */
             s->dev.started = false;
         }

hw/scsi/vhost-scsi.c

@@ -120,7 +120,7 @@ static void vhost_scsi_set_status(VirtIODevice *vdev, uint8_t val)
         start = false;
     }
 
-    if (vsc->dev.started == start) {
+    if (vhost_dev_is_started(&vsc->dev) == start) {
         return;
     }
 
@@ -147,7 +147,7 @@ static int vhost_scsi_pre_save(void *opaque)
 
     /* At this point, backend must be stopped, otherwise
      * it might keep writing to memory. */
-    assert(!vsc->dev.started);
+    assert(!vhost_dev_is_started(&vsc->dev));
 
     return 0;
 }

hw/scsi/vhost-user-scsi.c

@@ -49,7 +49,7 @@ static void vhost_user_scsi_set_status(VirtIODevice *vdev, uint8_t status)
     VHostSCSICommon *vsc = VHOST_SCSI_COMMON(s);
     bool start = (status & VIRTIO_CONFIG_S_DRIVER_OK) && vdev->vm_running;
 
-    if (vsc->dev.started == start) {
+    if (vhost_dev_is_started(&vsc->dev) == start) {
         return;
     }
 

hw/virtio/vhost-user-fs.c

@@ -20,6 +20,7 @@
 #include "hw/virtio/virtio-bus.h"
 #include "hw/virtio/virtio-access.h"
 #include "qemu/error-report.h"
+#include "hw/virtio/vhost.h"
 #include "hw/virtio/vhost-user-fs.h"
 #include "monitor/monitor.h"
 #include "sysemu/sysemu.h"
@@ -124,7 +125,7 @@ static void vuf_set_status(VirtIODevice *vdev, uint8_t status)
     VHostUserFS *fs = VHOST_USER_FS(vdev);
     bool should_start = virtio_device_started(vdev, status);
 
-    if (fs->vhost_dev.started == should_start) {
+    if (vhost_dev_is_started(&fs->vhost_dev) == should_start) {
         return;
     }
 

hw/virtio/vhost-user-i2c.c

@@ -95,7 +95,7 @@ static void vu_i2c_set_status(VirtIODevice *vdev, uint8_t status)
     VHostUserI2C *i2c = VHOST_USER_I2C(vdev);
     bool should_start = virtio_device_started(vdev, status);
 
-    if (i2c->vhost_dev.started == should_start) {
+    if (vhost_dev_is_started(&i2c->vhost_dev) == should_start) {
         return;
     }
 
@@ -174,7 +174,7 @@ static void vu_i2c_disconnect(DeviceState *dev)
     }
     i2c->connected = false;
 
-    if (i2c->vhost_dev.started) {
+    if (vhost_dev_is_started(&i2c->vhost_dev)) {
         vu_i2c_stop(vdev);
     }
 }

hw/virtio/vhost-user-rng.c

@@ -92,7 +92,7 @@ static void vu_rng_set_status(VirtIODevice *vdev, uint8_t status)
     VHostUserRNG *rng = VHOST_USER_RNG(vdev);
     bool should_start = virtio_device_started(vdev, status);
 
-    if (rng->vhost_dev.started == should_start) {
+    if (vhost_dev_is_started(&rng->vhost_dev) == should_start) {
         return;
     }
 
@@ -160,7 +160,7 @@ static void vu_rng_disconnect(DeviceState *dev)
 
     rng->connected = false;
 
-    if (rng->vhost_dev.started) {
+    if (vhost_dev_is_started(&rng->vhost_dev)) {
         vu_rng_stop(vdev);
     }
 }

hw/virtio/vhost-user-vsock.c

@@ -57,7 +57,7 @@ static void vuv_set_status(VirtIODevice *vdev, uint8_t status)
     VHostVSockCommon *vvc = VHOST_VSOCK_COMMON(vdev);
     bool should_start = virtio_device_started(vdev, status);
 
-    if (vvc->vhost_dev.started == should_start) {
+    if (vhost_dev_is_started(&vvc->vhost_dev) == should_start) {
         return;
     }
 

hw/virtio/vhost-vsock-common.c

@@ -14,6 +14,7 @@
 #include "hw/virtio/virtio-access.h"
 #include "qemu/error-report.h"
 #include "hw/qdev-properties.h"
+#include "hw/virtio/vhost.h"
 #include "hw/virtio/vhost-vsock.h"
 #include "qemu/iov.h"
 #include "monitor/monitor.h"
@@ -199,7 +200,7 @@ int vhost_vsock_common_pre_save(void *opaque)
      * At this point, backend must be stopped, otherwise
      * it might keep writing to memory.
      */
-    assert(!vvc->vhost_dev.started);
+    assert(!vhost_dev_is_started(&vvc->vhost_dev));
 
     return 0;
 }

hw/virtio/vhost-vsock.c

@@ -73,7 +73,7 @@ static void vhost_vsock_set_status(VirtIODevice *vdev, uint8_t status)
     bool should_start = virtio_device_started(vdev, status);
     int ret;
 
-    if (vvc->vhost_dev.started == should_start) {
+    if (vhost_dev_is_started(&vvc->vhost_dev) == should_start) {
         return;
     }
 

include/hw/virtio/vhost.h

@@ -94,6 +94,7 @@ struct vhost_dev {
     uint64_t protocol_features;
     uint64_t max_queues;
     uint64_t backend_cap;
+    /* @started: is the vhost device started? */
     bool started;
     bool log_enabled;
     uint64_t log_size;
@@ -165,6 +166,17 @@ int vhost_dev_enable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev);
  */
 void vhost_dev_disable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev);
 
+/**
+ * vhost_dev_is_started() - report status of vhost device
+ * @hdev: common vhost_dev structure
+ *
+ * Return the started status of the vhost device
+ */
+static inline bool vhost_dev_is_started(struct vhost_dev *hdev)
+{
+    return hdev->started;
+}
+
 /**
  * vhost_dev_start() - start the vhost device
  * @hdev: common vhost_dev structure