[RFC PATCH 17/17] KVM: PPC: Add an ioctl for userspace to select which platform to emulate

Alexander Graf agraf at suse.de
Sun Jul 3 19:09:21 EST 2011

On 03.07.2011, at 11:05, Avi Kivity wrote:

> On 07/03/2011 12:00 PM, Alexander Graf wrote:
>> >>          }
>> >>
>> >>  Otherwise we might write over data the user expected. And that logic that tells to copy_to_user how much data it actually takes to put all the information in is not there today and would have to be added. You can even verify that required_size with the ioctl passed size to make 100% sure user space is sane, but I'd claim that a feature bitmap is plenty of information to ensure that we're not doing something stupid.
>> >
>> >  I don't see why we have to caclulate something, then verify it against the correct answer.
>> Ah, I think I'm grasping your idea. You'd simply truncate the resulting struct according to the size passed by the ioctl and call it a day. Well, that works too. User space simply wouldn't be able to know if all information actually fit into the struct, but I guess that's fine :).
> Right.  The idea is that if KVM_FLAG_BLAH implies a field kvm_struct::blah, then either both are present in the headers, or none  of them.

Yup, makes sense. I like the idea :). Gets rid of all the useless paddings and reserved fields. We could even truncate the structs that already have paddings in them if we only copy min(sizeof(real_struct), ioctl_passed_size); (which we should anyways).

How long until we get a patch set? :)


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