[PATCH 3/3] vfio/migration: Make VFIO migration non-experimental

[Avihai Horon]

The major parts of VFIO migration are supported today in QEMU. This
includes basic VFIO migration, device dirty page tracking and precopy
support.

Thus, at this point in time, it seems appropriate to make VFIO migration
non-experimental: remove the x prefix from enable_migration property,
change it to ON_OFF_AUTO and let the default value be AUTO.

In addition, make the following adjustments:
1. Require device dirty tracking support when enable_migration is AUTO
   (i.e., not explicitly enabled). This is because device dirty tracking
   is currently the only method to do dirty page tracking, which is
   essential for migrating in a reasonable downtime. Setting
   enable_migration to ON will not require device dirty tracking.
2. Make migration blocker messages more elaborate.
3. Remove error prints in vfio_migration_query_flags().
4. Remove a redundant assignment in vfio_migration_realize().

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
---
 include/hw/vfio/vfio-common.h |  2 +-
 hw/vfio/migration.c           | 29 ++++++++++++++++-------------
 hw/vfio/pci.c                 |  4 ++--
 3 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
index b4c28f318f..387eabde60 100644
--- a/include/hw/vfio/vfio-common.h
+++ b/include/hw/vfio/vfio-common.h
@@ -139,7 +139,7 @@ typedef struct VFIODevice {
     bool needs_reset;
     bool no_mmap;
     bool ram_block_discard_allowed;
-    bool enable_migration;
+    OnOffAuto enable_migration;
     VFIODeviceOps *ops;
     unsigned int num_irqs;
     unsigned int num_regions;
diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 79eb81dfd7..d8e0848635 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -731,14 +731,6 @@ static int vfio_migration_query_flags(VFIODevice 
*vbasedev, uint64_t *mig_flags)
     feature->argsz = sizeof(buf);
     feature->flags = VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_MIGRATION;
     if (ioctl(vbasedev->fd, VFIO_DEVICE_FEATURE, feature)) {
-        if (errno == ENOTTY) {
-            error_report("%s: VFIO migration is not supported in kernel",
-                         vbasedev->name);
-        } else {
-            error_report("%s: Failed to query VFIO migration support, err: %s",
-                         vbasedev->name, strerror(errno));
-        }
-
         return -errno;
     }
 
@@ -831,14 +823,28 @@ void vfio_reset_bytes_transferred(void)
 
 int vfio_migration_realize(VFIODevice *vbasedev, Error **errp)
 {
-    int ret = -ENOTSUP;
+    int ret;
 
-    if (!vbasedev->enable_migration) {
+    if (vbasedev->enable_migration == ON_OFF_AUTO_OFF) {
+        error_setg(&vbasedev->migration_blocker,
+                   "%s: Migration is disabled for VFIO device", 
vbasedev->name);
         goto add_blocker;
     }
 
     ret = vfio_migration_init(vbasedev);
     if (ret) {
+        error_setg(&vbasedev->migration_blocker,
+                   "%s: Migration couldn't be initialized for VFIO device, "
+                   "err: %d (%s)",
+                   vbasedev->name, ret, strerror(-ret));
+        goto add_blocker;
+    }
+
+    if (vbasedev->enable_migration == ON_OFF_AUTO_AUTO &&
+        !vbasedev->dirty_pages_supported) {
+        error_setg(&vbasedev->migration_blocker,
+                   "%s: VFIO device doesn't support device dirty tracking",
+                   vbasedev->name);
         goto add_blocker;
     }
 
@@ -856,9 +862,6 @@ int vfio_migration_realize(VFIODevice *vbasedev, Error 
**errp)
     return 0;
 
 add_blocker:
-    error_setg(&vbasedev->migration_blocker,
-               "VFIO device doesn't support migration");
-
     ret = migrate_add_blocker(vbasedev->migration_blocker, errp);
     if (ret < 0) {
         error_free(vbasedev->migration_blocker);
diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 73874a94de..48584e3b01 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -3347,8 +3347,8 @@ static Property vfio_pci_dev_properties[] = {
                     VFIO_FEATURE_ENABLE_REQ_BIT, true),
     DEFINE_PROP_BIT("x-igd-opregion", VFIOPCIDevice, features,
                     VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT, false),
-    DEFINE_PROP_BOOL("x-enable-migration", VFIOPCIDevice,
-                     vbasedev.enable_migration, false),
+    DEFINE_PROP_ON_OFF_AUTO("enable-migration", VFIOPCIDevice,
+                            vbasedev.enable_migration, ON_OFF_AUTO_AUTO),
     DEFINE_PROP_BOOL("x-no-mmap", VFIOPCIDevice, vbasedev.no_mmap, false),
     DEFINE_PROP_BOOL("x-balloon-allowed", VFIOPCIDevice,
                      vbasedev.ram_block_discard_allowed, false),
-- 
2.26.3