From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 5/5] HPET interaction with in-kernel PIT (v6) Date: Sun, 14 Jun 2009 12:18:24 +0300 Message-ID: <4A34C060.8000100@redhat.com> References: <1244771206-19872-1-git-send-email-eak@us.ibm.com> <1244771206-19872-5-git-send-email-eak@us.ibm.com> <4A34BA88.7060204@redhat.com> <4A34BE92.6010302@web.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Beth Kon , kvm@vger.kernel.org To: Jan Kiszka Return-path: Received: from mx2.redhat.com ([66.187.237.31]:42257 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754232AbZFNJSZ (ORCPT ); Sun, 14 Jun 2009 05:18:25 -0400 In-Reply-To: <4A34BE92.6010302@web.de> Sender: kvm-owner@vger.kernel.org List-ID: Jan Kiszka wrote: >>> >>> struct kvm_pit_state { >>> struct kvm_pit_channel_state channels[3]; >>> + u8 hpet_legacy_mode; >>> }; >>> >>> >> This changes the ABI, breaking older binaries running on newer kernels, >> or newer binaries running on older kernels. >> > > As we have KVM_CREATE_PIT2 now, which includes struct kvm_pit_config > with a lot of unused flags, it should be straightforward to negotiate > the kvm_pit_state format between kernel and user space: kernel > advertises support for the new one via capability, user space requests > it via a bit in kvm_pit_state.flags. > We still need a new ioctl. The structure size is embedded in the ioctl number, so any additions automatically cause version mismatches. I sent patches some time ago to have the kernel automatically adjust for this, but they weren't well received. -- error compiling committee.c: too many arguments to function