Am 21.10.2010 23:37, schrieb Ryan Harper: > * 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).
So is this basically what blockdev_del is supposed to become one day? Copying Markus to have a look at this. I'm sure he has some thoughts on it as he was planning to implement blockdev_add/del. Kevin > > 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.