[Qemu-devel] [PATCH 3/3] vhost-scsi: Allow user to enable migration

[Nir Weiner]

From: Liran Alon <address@hidden>

Originally migration was not possible with vhost-scsi because
as part of migration, the source host target SCSI device state
needs to be saved and loaded into the destination host target SCSI
device. This cannot be done by QEMU.

As this can be handled either by external orchestrator or by having
shared-storage (i.e. iSCSI), there is no reason to limit the
orchestrator from being able to explictly specify it wish to enable
migration even when VM have a vhost-scsi device.

Reviewed-by: Nir Weiner <address@hidden>
Reviewed-by: Bijan Mottahedeh <address@hidden>
Signed-off-by: Liran Alon <address@hidden>
---
 hw/scsi/vhost-scsi.c                  | 30 ++++++++++++++++++---------
 include/hw/virtio/vhost-scsi-common.h |  1 +
 2 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/hw/scsi/vhost-scsi.c b/hw/scsi/vhost-scsi.c
index eb0cf9e1312f..52d46a788e6c 100644
--- a/hw/scsi/vhost-scsi.c
+++ b/hw/scsi/vhost-scsi.c
@@ -199,13 +199,18 @@ static void vhost_scsi_realize(DeviceState *dev, Error 
**errp)
         goto close_fd;
     }
 
-    error_setg(&vsc->migration_blocker,
-               "vhost-scsi does not support migration");
-    migrate_add_blocker(vsc->migration_blocker, &err);
-    if (err) {
-        error_propagate(errp, err);
-        error_free(vsc->migration_blocker);
-        goto close_fd;
+    if (!vsc->migratable) {
+        error_setg(&vsc->migration_blocker,
+                "vhost-scsi does not support migration in all cases."
+                "When external environment is supports it (Orchestrator 
migrates"
+                "target SCSI device state or use shared storage over network),"
+                "set 'migratable' property to true to enable migration.");
+        migrate_add_blocker(vsc->migration_blocker, &err);
+        if (err) {
+            error_propagate(errp, err);
+            error_free(vsc->migration_blocker);
+            goto close_fd;
+        }
     }
 
     vsc->dev.nvqs = VHOST_SCSI_VQ_NUM_FIXED + vs->conf.num_queues;
@@ -230,7 +235,9 @@ static void vhost_scsi_realize(DeviceState *dev, Error 
**errp)
     return;
 
  free_vqs:
-    migrate_del_blocker(vsc->migration_blocker);
+    if (!vsc->migratable) {
+        migrate_del_blocker(vsc->migration_blocker);
+    }
     g_free(vsc->dev.vqs);
  close_fd:
     close(vhostfd);
@@ -243,8 +250,10 @@ static void vhost_scsi_unrealize(DeviceState *dev, Error 
**errp)
     VHostSCSICommon *vsc = VHOST_SCSI_COMMON(dev);
     struct vhost_virtqueue *vqs = vsc->dev.vqs;
 
-    migrate_del_blocker(vsc->migration_blocker);
-    error_free(vsc->migration_blocker);
+    if (!vsc->migratable) {
+        migrate_del_blocker(vsc->migration_blocker);
+        error_free(vsc->migration_blocker);
+    }
 
     /* This will stop vhost backend. */
     vhost_scsi_set_status(vdev, 0);
@@ -268,6 +277,7 @@ static Property vhost_scsi_properties[] = {
     DEFINE_PROP_BIT64("t10_pi", VHostSCSICommon, host_features,
                                                  VIRTIO_SCSI_F_T10_PI,
                                                  false),
+    DEFINE_PROP_BOOL("migratable", VHostSCSICommon, migratable, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/include/hw/virtio/vhost-scsi-common.h 
b/include/hw/virtio/vhost-scsi-common.h
index 57fb1d87b51d..4eab767ee89f 100644
--- a/include/hw/virtio/vhost-scsi-common.h
+++ b/include/hw/virtio/vhost-scsi-common.h
@@ -36,6 +36,7 @@ typedef struct VHostSCSICommon {
     int target;
     int lun;
     uint64_t host_features;
+    bool migratable;
 } VHostSCSICommon;
 
 int vhost_scsi_common_start(VHostSCSICommon *vsc);
-- 
2.17.1