On Fri, Sep 6, 2013 at 4:04 PM, Marc Zyngier marc.zyngier@arm.com wrote:
On 2013-09-06 11:24, Alexander Graf wrote:
On 06.09.2013, at 12:05, Anup Patel wrote:
On Fri, Sep 6, 2013 at 2:24 PM, Alexander Graf agraf@suse.de wrote:
On 06.09.2013, at 09:44, Anup Patel wrote:
[...]
Another advantage I saw in extending KVM_ARM_VCPU_INIT ioctl is backward compatibility with current semantics. In other words, this patch does not break current KVMTOOL/QEMU and they can implement "-cpu host" whenever they wish without using any additional ioctl.
It's the opposite actually. By making the ioctl parameter in/out direction you change the ioctl number, breaking the ABI, no?
Originally the ioctl was only "in" and so we are preserving the "in" semantics. Thats why it is semantically backward compatible.
Great. So now we have an ioctl that says it's "in" in its ioctl descriptor, but really it's in/out. This really only works by accident because nobody is filtering the direction today.
Nack.
Agreed. We don't break the ABI, we don't try to fool the kernel. Please.
We are not breaking the ABI here and also not trying to fool the kernel.
There's been previous suggestions on how to implement this feature, please consider them.
I am not convinced about how is this approach not better.
M.-- Fast, cheap, reliable. Pick two.
--Anup