Re: [Qemu-devel] [Qemu-block] [PATCH] block: check BlockDriverState object before dereference

[Kevin Wolf <kwolf@redhat.com>]

Am 01.08.2017 um 10:35 hat Paolo Bonzini geschrieben:
> On 01/08/2017 02:14, John Snow wrote:
> > I may need some nudging towards understanding what the right solution
> > here is, though. Should the blk_aio_flush assume that there always is a
> > root BDS? should it not assume that?
> 
> I think blk_aio_flush is not special.  If there is no root BDS, either
> you return -ENOMEDIUM, or you crash.  But all functions should be doing
> the same.

The intended semantics is that they return -ENOMEDIUM (or fail at
least). This is how things have always worked, and that it crashes now
because of the bdrv_inc_in_flight() was not an intentional change, but
simply a bug in the patch.

> The former makes sense, but right now blk_prwv for one are crashing if
> there is no root BDS so the minimum patch would fix the caller rather
> than blk_aio_flush.

The synchronous versions don't crash, and bdrv_aio_prwv() would fix all
cases if bdrv_inc_in_flight() were moved inside the coroutine; probably
right before blk_aio_complete(). This would be more consistent with how
the synchronous versions work, too, increasing the in-flight count only
by 1 rather than 2 for an AIO request.

Kevin