Kevin Wolf <kw...@redhat.com> writes: > 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.
Yes, Ryan's drive_unplug is quite close to my blockdev_del. However, my blockdev_del is part of a more ambitious job, namely to cleanly separate host and guest part of block devices. A whole lot of preliminary cleanups have made it in so far, but not the actual commands. I'll reply in more detail to the latest version of the patch series. [...]
