From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [PATCH] virtio-balloon spec: provide a version of the "silent deflate" feature that works Date: Fri, 07 Sep 2012 09:15:46 +0930 Message-ID: <87wr06hg0l.fsf@rustcorp.com.au> References: <1346917610-14568-1-git-send-email-pbonzini@redhat.com> <20120906084736.GF17656@redhat.com> <50486BB2.7070108@redhat.com> <20120906094442.GA22816@redhat.com> <50487382.8030303@redhat.com> <20120906105301.GC32325@redhat.com> <5048935A.8090308@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5048935A.8090308@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Paolo Bonzini , "Michael S. Tsirkin" Cc: fes@google.com, aarcange@redhat.com, riel@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mikew@google.com, yinghan@google.com, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org Paolo Bonzini writes: > Instead, VIRTIO_NET_F_HOST_MUST_SEND_GARP would be a "negative" feature: > if set, the host _may not_ rely on the guest to send a gARP. Similarly > if VIRTIO_BALLOON_F_MUST_TELL_HOST is set, the guest _may not_ use > ballooned pages directly. > > There are _no_ other negative features besides > VIRTIO_BALLOON_F_MUST_TELL_HOST in the spec, and for a good > reason---because they're broken. > > (Hmm, actually we have one, VIRTIO_BLK_F_RO. It is also a bit broken, > but it is not so important because it depends on user input more than > hypervisor version). Yes, this is the key observation, and an important lesson for the future. Thanks! Note that these two negative features were in the original spec, where it's assumed that every device supports them. That's not explicitly documented, however. I like killing the totally unused feature. Cheers, Rusty.