[V1,22/26] vfio/iommufd: invariant device name

Commit Message

Steven Sistare Jan. 29, 2025, 2:43 p.m. UTC

cpr-transfer will use the device name as a key to find the value
of the device descriptor in new QEMU.  However, if the descriptor
number is specified by a command-line fd parameter, then
vfio_device_get_name creates a name that includes the fd number.
This causes a chicken-and-egg problem: new QEMU must know the fd
number to construct a name to find the fd number.

To fix, create an invariant name based on the id command-line
parameter.  If id is not defined, add a CPR blocker.

Signed-off-by: Steve Sistare <[e-mail]>
---
 hw/vfio/helpers.c             | 18 +++++++++++++++---
 hw/vfio/iommufd.c             |  2 ++
 include/hw/vfio/vfio-common.h |  1 +
 3 files changed, 18 insertions(+), 3 deletions(-)

Patch

diff --git a/hw/vfio/helpers.c b/hw/vfio/helpers.c
index 913796f..bd94b86 100644
--- a/hw/vfio/helpers.c
+++ b/hw/vfio/helpers.c
@@ -25,6 +25,8 @@ 
 #include "hw/vfio/vfio-common.h"
 #include "hw/hw.h"
 #include "trace.h"
+#include "migration/blocker.h"
+#include "migration/cpr.h"
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "qemu/units.h"
@@ -636,6 +638,7 @@  bool vfio_device_get_name(VFIODevice *vbasedev, Error **errp)
 {
     ERRP_GUARD();
     struct stat st;
+    bool ret = true;
 
     if (vbasedev->fd < 0) {
         if (stat(vbasedev->sysfsdev, &st) < 0) {
@@ -653,15 +656,24 @@  bool vfio_device_get_name(VFIODevice *vbasedev, Error **errp)
             return false;
         }
         /*
-         * Give a name with fd so any function printing out vbasedev->name
+         * Give a name so any function printing out vbasedev->name
          * will not break.
          */
         if (!vbasedev->name) {
-            vbasedev->name = g_strdup_printf("VFIO_FD%d", vbasedev->fd);
+            if (vbasedev->dev->id) {
+                vbasedev->name = g_strdup(vbasedev->dev->id);
+            } else {
+                vbasedev->name = g_strdup_printf("VFIO_FD%d", vbasedev->fd);
+                error_setg(&vbasedev->cpr_id_blocker,
+                           "vfio device with fd=%d needs an id property",
+                           vbasedev->fd);
+                ret = migrate_add_blocker_modes(&vbasedev->cpr_id_blocker, errp,
+                                                MIG_MODE_CPR_TRANSFER, -1) == 0;
+            }
         }
     }
 
-    return true;
+    return ret;
 }
 
 void vfio_device_set_fd(VFIODevice *vbasedev, const char *str, Error **errp)
diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
index 2f888e5..8308715 100644
--- a/hw/vfio/iommufd.c
+++ b/hw/vfio/iommufd.c
@@ -24,6 +24,7 @@ 
 #include "system/reset.h"
 #include "qemu/cutils.h"
 #include "qemu/chardev_open.h"
+#include "migration/blocker.h"
 #include "pci.h"
 #include "exec/ram_addr.h"
 
@@ -657,6 +658,7 @@  static void iommufd_cdev_detach(VFIODevice *vbasedev)
     iommufd_cdev_container_destroy(container);
     vfio_put_address_space(space);
 
+    migrate_del_blocker(&vbasedev->cpr_id_blocker);
     iommufd_cdev_unbind_and_disconnect(vbasedev);
     close(vbasedev->fd);
 }
diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
index ca10abc..37e7c26 100644
--- a/include/hw/vfio/vfio-common.h
+++ b/include/hw/vfio/vfio-common.h
@@ -147,6 +147,7 @@  typedef struct VFIODevice {
     VFIOMigration *migration;
     Error *migration_blocker;
     Error *cpr_mdev_blocker;
+    Error *cpr_id_blocker;
     OnOffAuto pre_copy_dirty_page_tracking;
     OnOffAuto device_dirty_page_tracking;
     bool dirty_pages_supported;