From mboxrd@z Thu Jan 1 00:00:00 1970 From: Badari Pulavarty Subject: Re: [PATCH] virtio-blk: allow toggling host cache between writeback and writethrough Date: Thu, 05 Jul 2012 11:39:10 -0700 Message-ID: <1341513550.5508.7.camel@badari-desktop> References: <1341321577-24435-1-git-send-email-pbonzini@redhat.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, rusty@rustcorp.com.au, kvm@vger.kernel.org To: Paolo Bonzini Return-path: In-Reply-To: <1341321577-24435-1-git-send-email-pbonzini@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Tue, 2012-07-03 at 15:19 +0200, Paolo Bonzini wrote: > This patch adds support for the new VIRTIO_BLK_F_CONFIG_WCE feature, > which exposes the cache mode in the configuration space and lets the > driver modify it. The cache mode is exposed via sysfs. > > Even if the host does not support the new feature, the cache mode is > visible (thanks to the existing VIRTIO_BLK_F_WCE), but not modifiable. > > Signed-off-by: Paolo Bonzini > --- Hi Paolo, Curious - What is the host side change to support this ? QEMU would close and re-open the device/file with the corresponding flags (O_SYNC) ? And also, is there a way to expose cache=none (O_DIRECT) to the guest ? Our cluster filesystem folks need a way to verify/guarantee that virtio-blk device has cache=none selected at host. Otherwise, they can not support a cluster filesystem running inside a VM (on virtio-blk). Thoughts ? Thanks, Badari