On Thu, Sep 05, 2013 at 02:05:09PM +1000, Benjamin Herrenschmidt wrote: > On Tue, 2013-09-03 at 13:53 +0300, Gleb Natapov wrote: > > > Or supporting all IOMMU links (and leaving emulated stuff as is) in on > > > "device" is the last thing I have to do and then you'll ack the patch? > > > > > I am concerned more about API here. Internal implementation details I > > leave to powerpc experts :) > > So Gleb, I want to step in for a bit here. > > While I understand that the new KVM device API is all nice and shiny and that this > whole thing should probably have been KVM devices in the first place (had they > existed or had we been told back then), the point is, the API for handling > HW IOMMUs that Alexey is trying to add is an extension of an existing mechanism > used for emulated IOMMUs. > > The internal data structure is shared, and fundamentally, by forcing him to > use that new KVM device for the "new stuff", we create a oddball API with > an ioctl for one type of iommu and a KVM device for the other, which makes > the implementation a complete mess in the kernel (and you should care :-) > Is it unfixable mess? Even if Alexey will do what you suggested earlier? - Convert *both* existing TCE objects to the new KVM_CREATE_DEVICE, and have some backward compat code for the old one. The point is implementation usually can be changed, but for API it is much harder to do so. > So for something completely new, I would tend to agree with you. However, I > still think that for this specific case, we should just plonk-in the original > ioctl proposed by Alexey and be done with it. > Do you think this is the last extension to IOMMU code, or we will see more and will use same justification to continue adding ioctls? -- Gleb. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>