Re: [Qemu-devel] [PATCH 2/2] v2 Fix Block Hotplug race with drive_unplug()

[Daniel P. Berrange]

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 ?

Regards,
Daniel
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