[RFC v2 3/3] libvhost-user: fence legacy virtio devices

[Marc Hartmayer <mhartmay@linux.ibm.com>]

libvhost-user has no support for legacy virtio devices therefore
let's fence them.

Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
---
 contrib/libvhost-user/libvhost-access.h | 10 ++++++++++
 contrib/libvhost-user/libvhost-user.c   |  6 ++++++
 2 files changed, 16 insertions(+)

diff --git a/contrib/libvhost-user/libvhost-access.h b/contrib/libvhost-user/libvhost-access.h
index 868ba3e7bfb8..aa505ea1ec02 100644
--- a/contrib/libvhost-user/libvhost-access.h
+++ b/contrib/libvhost-user/libvhost-access.h
@@ -1,11 +1,21 @@
 #ifndef LIBVHOST_ACCESS_H
 
+#include <assert.h>
+
 #include "qemu/bswap.h"
 
 #include "libvhost-user.h"
 
+static inline bool vu_has_feature(VuDev *dev, unsigned int fbit);
+
 static inline bool vu_access_is_big_endian(VuDev *dev)
 {
+    /*
+     * TODO: can probably be removed as the fencing is already done in
+     * `vu_set_features_exec`
+     */
+    assert(vu_has_feature(dev, VIRTIO_F_VERSION_1));
+
     /* Devices conforming to VIRTIO 1.0 or later are always LE. */
     return false;
 }
diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
index 0214b04c5291..93c4503b1f53 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -540,6 +540,12 @@ vu_set_features_exec(VuDev *dev, VhostUserMsg *vmsg)
     DPRINT("u64: 0x%016"PRIx64"\n", vmsg->payload.u64);
 
     dev->features = vmsg->payload.u64;
+    if (!vu_has_feature(dev, VIRTIO_F_VERSION_1)) {
+        /* We only support devices conforming to VIRTIO 1.0 or
+         * later */
+        vu_panic(dev, "virtio legacy devices aren't supported by libvhost-user");
+        return false;
+    }
 
     if (!(dev->features & VHOST_USER_F_PROTOCOL_FEATURES)) {
         vu_set_enable_all_rings(dev, true);
-- 
2.25.4