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

[Stefan Hajnoczi]

On Tue, Oct 19, 2010 at 3:32 PM, Ryan Harper <address@hidden> 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.
>
> Changes since v1:
> - Added qemu_aio_flush() before bdrv_flush() to wait on pending io
>
> Signed-off-by: Ryan Harper <address@hidden>
> ---
>  block.c         |    7 +++++++
>  block.h         |    1 +
>  blockdev.c      |   26 ++++++++++++++++++++++++++
>  blockdev.h      |    1 +
>  hmp-commands.hx |   15 +++++++++++++++
>  5 files changed, 50 insertions(+), 0 deletions(-)

Looks good to me.

Stefan