Re: [Qemu-devel] [PATCH v2 1/2] virtio: Add function to check whether backend supports VIRTIO_1

[Maxime Coquelin]

On 09/09/2016 07:47 PM, Michael S. Tsirkin wrote:

On Fri, Sep 09, 2016 at 08:00:31PM +0300, Marcel Apfelbaum wrote:

On 09/09/2016 04:10 PM, Maxime Coquelin wrote:

This patch adds virtio_test_backend_virtio_1() function to
check whether backend supports VIRTIO_F_VERSION_1 before the
negociation takes place.

Cc: Cornelia Huck <cornelia.h...@de.ibm.com>
Cc: Marcel Apfelbaum <mar...@redhat.com>
Cc: Michael S. Tsirkin <m...@redhat.com>
Cc: qemu-sta...@nongnu.org
Signed-off-by: Maxime Coquelin <maxime.coque...@redhat.com>
---
 hw/virtio/virtio.c         | 13 +++++++++++++
 include/hw/virtio/virtio.h |  1 +
 2 files changed, 14 insertions(+)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 74c085c..8b30b69 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -1481,6 +1481,19 @@ void virtio_vmstate_save(QEMUFile *f, void *opaque, 
size_t size)
     virtio_save(VIRTIO_DEVICE(opaque), f);
 }

+bool virtio_test_backend_virtio_1(VirtIODevice *vdev, Error **errp)
+{
+    VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
+    uint64_t feature;
+

I would set "feature = 0" even if doesn't really matter.
Anyway:

Reviewed-by: Marcel Apfelbaum <mar...@redhat.com>

Thanks,
Marcel

why wouldn't it matter? Looks like an uninitialized variable to me.

Oh yes, you are right, it should be initialized.
Just wait confirmation from Michael on the RFC before sending a v3.

Thanks,
Maxime

+    virtio_add_feature(&feature, VIRTIO_F_VERSION_1);
+
+    assert(k->get_features != NULL);
+    feature = k->get_features(vdev, feature, errp);
+
+    return virtio_has_feature(feature, VIRTIO_F_VERSION_1);
+}
+
 static int virtio_set_features_nocheck(VirtIODevice *vdev, uint64_t val)
 {
     VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index d2490c1..3a31754 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -235,6 +235,7 @@ int virtio_set_status(VirtIODevice *vdev, uint8_t val);
 void virtio_reset(void *opaque);
 void virtio_update_irq(VirtIODevice *vdev);
 int virtio_set_features(VirtIODevice *vdev, uint64_t val);
+bool virtio_test_backend_virtio_1(VirtIODevice *vdev, Error **errp);

 /* Base devices.  */
 typedef struct VirtIOBlkConf VirtIOBlkConf;