Re: [Qemu-devel] qom and debug (was: [PATCH for 2.8 02/11] virtio: convert to use DMA api)

[Michael S. Tsirkin]

On Tue, Aug 30, 2016 at 01:11:05PM +0200, Cornelia Huck wrote:
> On Tue, 30 Aug 2016 13:21:23 +0300
> "Michael S. Tsirkin" <address@hidden> wrote:
> 
> > BTW downstreams are building with --disable-qom-cast-debug which drops
> > all QOM casts on data path - one way is to say we just make this the
> > default upstream as well. Another to say that we want to distinguish
> > fast path calls from slow path, this way we will be able to bring back
> > some of the checks.
> 
> I find CONFIG_QOM_CAST_DEBUG a bit inconsistent, btw:
> 
> - for object casts, we optimize away all checks and just return the
> object for !debug
> - for class casts, we optimize away only the caching and still keep the
> checking (why would we drop the caching if this can speed up things?)
> 
> We certainly want to have debug turned on during development to avoid
> nasty surprises later (otherwise, why even bother?), but it makes sense
> to turn it off for a release. (Is there an easy way to turn it off for
> the release, normal or stable, and keep it during the development
> cycle?)

I think the assumption was class casts are not on data path.
Ideally we'd keep it on for release too for non-datapath things,
to help improve security.

-- 
MST