* Daniel P. Berrange <berra...@redhat.com> [2010-10-21 08:29]: > On Tue, Oct 19, 2010 at 09:32:29AM -0500, Ryan Harper wrote: > > Block hot unplug is racy since the guest is required to acknowlege the ACPI > > unplug event; this may not happen synchronously with the device removal > > command > > > > This series aims to close a gap where by mgmt applications that assume the > > block resource has been removed without confirming that the guest has > > acknowledged the removal may re-assign the underlying device to a second > > guest > > leading to data leakage. > > > > This series introduces a new montor command to decouple asynchornous device > > removal from restricting guest access to a block device. We do this by > > creating > > a new monitor command drive_unplug which maps to a bdrv_unplug() command > > which > > does a qemu_aio_flush; bdrv_flush() and bdrv_close(). Once complete, > > subsequent > > IO is rejected from the device and the guest will get IO errors but > > continue to > > function. > > > > A subsequent device removal command can be issued to remove the device, to > > which > > the guest may or maynot respond, but as long as the unplugged bit is set, > > no IO > > will be sumbitted. > > The name 'drive_unplug' suggests to me that the drive object is > not being deleted/free()d ? Is that correct understanding, and if > so, what is responsible for finally free()ing the drive backend ?
It's technically the BlockDriverState Driver that we're closing. To fully release the remaining resources, a device_del is required (which of course requires guest participation with the current interface). Once QEMU issues the removal request, the guest responds and the piix4 acpi handler for pciej_write writes invokes qdev_free() on the target device. qdev_free() on the pci device will make it's way to the qdev exit handler registered for virtio-blk devices, virtio_blk_exit_pci(). virtio_blk_exit_pci() marks the drive structure for deletion. When qdev calls the properties handler, it invokes free_drive() on the disk and that calls blockdev_auto_del() which will do a bdrv_delete() which nukes the remaining objects (the acutal BlockDriverState). I think I got the whole path in there. -- Ryan Harper Software Engineer; Linux Technology Center IBM Corp., Austin, Tx ry...@us.ibm.com
