On Wed, Dec 15, 2021 at 10:35:30AM -0500, Jagannathan Raman wrote: > @@ -150,6 +157,38 @@ static void vfu_object_init_ctx(VfuObject *o, Error > **errp) > + o->pci_dev = PCI_DEVICE(dev); ... > @@ -190,6 +229,8 @@ static void vfu_object_finalize(Object *obj) > > o->device = NULL; > > + o->pci_dev = NULL;
We need to consider how this interacts with device_del hot unplug. o->pci_dev is a pointer and we don't hold a refcount, so I think o->pci_dev could disappear at any moment. A pair of object_ref/unref(OBJECT(o->pci_dev)) calls would not be enough because device_del will still unrealize the device that's in use by the vfio-user server. I suggest adding a check to qdev_unplug() that prevents unplug when the device is in use by the vfio-user server. That's similar to the code in that function for preventing unplug during migration. One way to do that is by adding a new API: /* * Register an Error that is raised when unplug is attempted on a * device. If another blocker has already been registered then that * Error may be raised during unplug instead. * * qdev_del_unplug_blocker() must be called to remove this blocker. */ void qdev_add_unplug_blocker(DeviceState *dev, Error *blocker); /* * Deregister an Error that was previously registered with * qdev_add_unplug_blocker(). */ void qdev_del_unplug_blocker(DeviceState *dev, Error *blocker); The vfio-user server then needs to add an Error *unplug_blocker field to VfuObject and call qdev_add/del_unplug_blocker() on the PCI device. >From a user perspective this means that device_del fails with "Device currently in use by vfio-user server '%s'". Stefan
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