Re: [RFC 0/5] Making KVM_GET_ONE_REG/KVM_SET_ONE_REG generic.

[Avi Kivity <avi@redhat.com>]

On 09/03/2012 03:33 PM, Rusty Russell wrote:
> Avi Kivity <avi@redhat.com> writes:
>> On 09/01/2012 03:35 PM, Rusty Russell wrote:
>>> Passing an address in a struct is pretty bad, since it involves
>>> compatibility wrappers.  
>>
>> Right, some s390 thing.
> 
> Err, no, i386 on x86-64, or ppc32 on ppc64, or arm on arm64....
> 
> Any time you put a pointer in a structure which is exposed to userspace,
> you have to deal with this.

Not is you pack the pointer in a __u64, which is what we do to preserve
padding.  Then it is only s390 which needs extra love.

>>> I don't think that is what makes the API hard
>>> to use.
>>
>> What is it then?  I forgot what the original complaints/complainers were.
> 
> I have no idea, since I didn't hear the complaints.  But any non-fixed
> size array has issues in C; there's not much we can do about it.
> 
> x86 manages this fine for msrs, and I didn't have a problem using it for
> my test programs.  That's the limit of my experience, however.

Another option is to use the size parameter from the ioctl.  It just
sits there doing nothing.

-- 
error compiling committee.c: too many arguments to function