On Mon, May 21, 2012 at 05:08:29PM +0800, Asias He wrote:

When user hot-unplug a disk which is busy serving I/O, __blk_run_queue
might be unable to drain all the requests. As a result, the
blk_drain_queue() would loop forever and blk_cleanup_queue would not
return. So hot-unplug will fail.

This patch adds a callback in blk_drain_queue() for low lever driver to
abort requests.

Currently, this is useful for virtio-blk to do cleanup in hot-unplug.

Why is this necessary?  virtio-blk should know that the device is gone
and fail in-flight / new commands.  That's what other drivers do.
What makes virtio-blk different?

Thanks.

-- 
tejun