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

[Cornelia Huck]

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?)