From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40966) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aRg1m-0000OA-3H for qemu-devel@nongnu.org; Fri, 05 Feb 2016 08:02:25 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aRg1i-00066N-1p for qemu-devel@nongnu.org; Fri, 05 Feb 2016 08:02:22 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49736) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aRg1h-00065y-Rx for qemu-devel@nongnu.org; Fri, 05 Feb 2016 08:02:17 -0500 References: <20160205103927.21017.26364.stgit@bahia.huguette.org> <20160205104559.21017.3686.stgit@bahia.huguette.org> From: Laurent Vivier Message-ID: <56B49D56.1050406@redhat.com> Date: Fri, 5 Feb 2016 14:02:14 +0100 MIME-Version: 1.0 In-Reply-To: <20160205104559.21017.3686.stgit@bahia.huguette.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v4 5/6] vhost: simplify vhost_needs_vring_endian() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Greg Kurz , "Michael S. Tsirkin" Cc: Cornelia Huck , qemu-devel@nongnu.org On 05/02/2016 11:46, Greg Kurz wrote: > After the call to virtio_vdev_has_feature(), we only care for legacy > devices, so we don't need the extra check in virtio_is_big_endian(). > > Also the device_endian field is always set (VIRTIO_DEVICE_ENDIAN_UNKNOWN > may only happen on a virtio_load() path that cannot lead here), so we > don't need the assert() either. > > This open codes the device_endian checking in vhost_needs_vring_endian(). > It also adds a comment to explain the logic, as recent reviews showed the > cross-endian tweaks aren't that obvious. > > Signed-off-by: Greg Kurz Reviewed-by: Laurent Vivier > --- > hw/virtio/vhost.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > index bb17177f5e7e..9f8ac38ccf2d 100644 > --- a/hw/virtio/vhost.c > +++ b/hw/virtio/vhost.c > @@ -749,6 +749,11 @@ static void vhost_log_stop(MemoryListener *listener, > /* FIXME: implement */ > } > > +/* The vhost driver natively knows how to handle the vrings of non > + * cross-endian legacy devices and modern devices. Only legacy devices > + * exposed to a bi-endian guest may require the vhost driver to use a > + * specific endianness. > + */ > static inline bool vhost_needs_vring_endian(VirtIODevice *vdev) > { > if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) { > @@ -756,9 +761,9 @@ static inline bool vhost_needs_vring_endian(VirtIODevice *vdev) > } > #ifdef TARGET_IS_BIENDIAN > #ifdef HOST_WORDS_BIGENDIAN > - return !virtio_is_big_endian(vdev); > + return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_LITTLE; > #else > - return virtio_is_big_endian(vdev); > + return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG; > #endif > #else > return false; > >