On Mon, Oct 18, 2010 at 11:17 PM, Ryan Harper <ry...@us.ibm.com> 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 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.
>
> Signed-off-by: Ryan Harper <ry...@us.ibm.com>
> ---
> block.c | 6 ++++++
> block.h | 1 +
> blockdev.c | 26 ++++++++++++++++++++++++++
> blockdev.h | 1 +
> hmp-commands.hx | 15 +++++++++++++++
> 5 files changed, 49 insertions(+), 0 deletions(-)
>
> diff --git a/block.c b/block.c
> index a19374d..9fedb27 100644
> --- a/block.c
> +++ b/block.c
> @@ -1328,6 +1328,12 @@ void bdrv_set_removable(BlockDriverState *bs, int
> removable)
> }
> }
>
> +void bdrv_unplug(BlockDriverState *bs)
> +{
> + bdrv_flush(bs);
> + bdrv_close(bs);
bdrv_flush() does not wait for pending aio requests to complete.
bdrv_close() does not wait either.
A VM with a qcow2 image file and pending aio requests could
bdrv_unplug() and free the qcow2 state before aio completions occur.
If a completion is handled after bdrv_close(), the qcow2 in-memory
state has been freed and we get memory corruption or a crash.
I think the solution is to use qemu_aio_flush() before bdrv_flush().
I waits until all pending aio requests have been completed.
Stefan
