[V2,36/45] vfio/iommufd: invariant device name

Commit Message

Steven Sistare Feb. 14, 2025, 2:14 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/cpr.c              | 21 +++++++++++++++++++++
 hw/vfio/helpers.c          | 10 ++++------
 hw/vfio/iommufd.c          |  2 ++
 include/hw/vfio/vfio-cpr.h |  4 ++++
 4 files changed, 31 insertions(+), 6 deletions(-)

Patch

diff --git a/hw/vfio/cpr.c b/hw/vfio/cpr.c
index a2400ca..e3ea2bf 100644
--- a/hw/vfio/cpr.c
+++ b/hw/vfio/cpr.c
@@ -11,6 +11,7 @@ 
 #include "hw/vfio/pci.h"
 #include "hw/pci/msix.h"
 #include "hw/pci/msi.h"
+#include "migration/blocker.h"
 #include "migration/cpr.h"
 #include "qapi/error.h"
 #include "system/runstate.h"
@@ -184,3 +185,23 @@  const VMStateDescription vfio_cpr_pci_vmstate = {
         VMSTATE_END_OF_LIST()
     }
 };
+
+bool vfio_cpr_set_device_name(VFIODevice *vbasedev, Error **errp)
+{
+    if (vbasedev->dev->id) {
+        vbasedev->name = g_strdup(vbasedev->dev->id);
+        return true;
+    } else {
+        /*
+         * Assign a name so any function printing it will not break, but the
+         * fd number changes across processes, so this cannot be used as an
+         * invariant name for CPR.
+         */
+        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);
+        return migrate_add_blocker_modes(&vbasedev->cpr.id_blocker, errp,
+                                         MIG_MODE_CPR_TRANSFER, -1) == 0;
+    }
+}
diff --git a/hw/vfio/helpers.c b/hw/vfio/helpers.c
index 4b255d4..4ff794c 100644
--- a/hw/vfio/helpers.c
+++ b/hw/vfio/helpers.c
@@ -29,6 +29,7 @@ 
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "qemu/units.h"
+#include "migration/cpr.h"
 #include "monitor/monitor.h"
 
 /*
@@ -637,6 +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) {
@@ -653,16 +655,12 @@  bool vfio_device_get_name(VFIODevice *vbasedev, Error **errp)
             error_setg(errp, "Use FD passing only with iommufd backend");
             return false;
         }
-        /*
-         * Give a name with fd so any function printing out vbasedev->name
-         * will not break.
-         */
         if (!vbasedev->name) {
-            vbasedev->name = g_strdup_printf("VFIO_FD%d", vbasedev->fd);
+            ret = vfio_cpr_set_device_name(vbasedev, errp);
         }
     }
 
-    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 7c0cdd7..2de2811 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"
 
@@ -661,6 +662,7 @@  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-cpr.h b/include/hw/vfio/vfio-cpr.h
index a9f2fbe..8a30d30 100644
--- a/include/hw/vfio/vfio-cpr.h
+++ b/include/hw/vfio/vfio-cpr.h
@@ -22,12 +22,14 @@  typedef struct VFIOContainerCPR {
 typedef struct VFIODeviceCPR {
     bool reused;
     Error *mdev_blocker;
+    Error *id_blocker;
 } VFIODeviceCPR;
 
 struct VFIOContainer;
 struct VFIOGroup;
 struct VFIOContainerBase;
 struct VFIOPCIDevice;
+struct VFIODevice;
 
 int vfio_cpr_reboot_notifier(NotifierWithReturn *notifier, MigrationEvent *e,
                              Error **errp);
@@ -53,4 +55,6 @@  void vfio_cpr_delete_vector_fd(struct VFIOPCIDevice *vdev, const char *name,
                                int nr);
 
 extern const VMStateDescription vfio_cpr_pci_vmstate;
+
+bool vfio_cpr_set_device_name(struct VFIODevice *vbasedev, Error **errp);
 #endif