[PATCH RFC 09/16] vhost-backend: implement extended features support.

[Paolo Abeni]

Leverage the kernel extended features manipulation ioctls(), if
available, and fallback to old ops otherwise. Error out when setting
extended features but kernel support is not available.

Note that extended support for get/set backend features is not needed,
as the only feature that can be changed belongs to the 64 bit range.

Signed-off-by: Paolo Abeni <pab...@redhat.com>
---
 hw/virtio/vhost-backend.c | 59 +++++++++++++++++++++++++++++++++++----
 1 file changed, 53 insertions(+), 6 deletions(-)

diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
index 833804dd40..a5e28e15ee 100644
--- a/hw/virtio/vhost-backend.c
+++ b/hw/virtio/vhost-backend.c
@@ -182,12 +182,6 @@ static int vhost_kernel_get_vring_worker(struct vhost_dev 
*dev,
     return vhost_kernel_call(dev, VHOST_GET_VRING_WORKER, worker);
 }
 
-static int vhost_kernel_set_features(struct vhost_dev *dev,
-                                     uint64_t features)
-{
-    return vhost_kernel_call(dev, VHOST_SET_FEATURES, &features);
-}
-
 static int vhost_kernel_set_backend_cap(struct vhost_dev *dev)
 {
     uint64_t features;
@@ -210,11 +204,59 @@ static int vhost_kernel_set_backend_cap(struct vhost_dev 
*dev)
     return 0;
 }
 
+#ifdef CONFIG_INT128
+static int vhost_kernel_set_features_ex(struct vhost_dev *dev,
+                                     virtio_features_t features)
+{
+    uint64_t features64;
+    int r;
+
+    /*
+     * Can't check for ENOTTY, as the kernel for unknown ioctls interprets
+     * the argument as a virtio queue id and most likely errors out validating
+     * such id, instead of reporting an unknown operation.
+     */
+    r = vhost_kernel_call(dev, VHOST_SET_FEATURES_EX, &features);
+    if (!r) {
+        return 0;
+    }
+
+    if (!!(features >> 64)) {
+        error_report("Trying to set extended features without kernel support");
+        return -EINVAL;
+    }
+    features64 = (uint64_t)features;
+    return vhost_kernel_call(dev, VHOST_SET_FEATURES, &features64);
+}
+
+static int vhost_kernel_get_features_ex(struct vhost_dev *dev,
+                                        virtio_features_t *features)
+{
+    uint64_t features64;
+    int r;
+
+    r = vhost_kernel_call(dev, VHOST_GET_FEATURES_EX, features);
+    if (!r) {
+        return 0;
+    }
+
+    r = vhost_kernel_call(dev, VHOST_GET_FEATURES, &features64);
+    *features = features64;
+    return r;
+}
+#else
+static int vhost_kernel_set_features(struct vhost_dev *dev,
+                                     uint64_t features)
+{
+    return vhost_kernel_call(dev, VHOST_SET_FEATURES, &features);
+}
+
 static int vhost_kernel_get_features(struct vhost_dev *dev,
                                      uint64_t *features)
 {
     return vhost_kernel_call(dev, VHOST_GET_FEATURES, features);
 }
+#endif
 
 static int vhost_kernel_set_owner(struct vhost_dev *dev)
 {
@@ -341,8 +383,13 @@ const VhostOps kernel_ops = {
         .vhost_attach_vring_worker = vhost_kernel_attach_vring_worker,
         .vhost_new_worker = vhost_kernel_new_worker,
         .vhost_free_worker = vhost_kernel_free_worker,
+#ifdef CONFIG_INT128
+        .vhost_set_features_ex = vhost_kernel_set_features_ex,
+        .vhost_get_features_ex = vhost_kernel_get_features_ex,
+#else
         .vhost_set_features = vhost_kernel_set_features,
         .vhost_get_features = vhost_kernel_get_features,
+#endif
         .vhost_set_backend_cap = vhost_kernel_set_backend_cap,
         .vhost_set_owner = vhost_kernel_set_owner,
         .vhost_get_vq_index = vhost_kernel_get_vq_index,
-- 
2.49.0