From: Paolo Abeni <pabeni@redhat.com>

The virtio specifications allows for up to 128 bits for the
device features. Soon we are going to use some of the 'extended'
bits features (bit 64 and above) for the virtio net driver.

Represent the virtio features bitmask with a fixed size array, and
introduce a few helpers to help manipulate them.

Most drivers will keep using only 64 bits features space: use union
to allow them access the lower part of the extended space without any
per driver change.

Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <6a9bbb5eb33830f20afbcb7e64d300af4126dd98.1758549625.git.pabeni@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 include/hw/virtio/virtio-features.h | 126 ++++++++++++++++++++++++++++
 include/hw/virtio/virtio.h          |   7 +-
 2 files changed, 130 insertions(+), 3 deletions(-)
 create mode 100644 include/hw/virtio/virtio-features.h

diff --git a/include/hw/virtio/virtio-features.h b/include/hw/virtio/virtio-features.h
new file mode 100644
index 0000000000..e29b7fe48f
--- /dev/null
+++ b/include/hw/virtio/virtio-features.h
@@ -0,0 +1,126 @@
+/*
+ * Virtio features helpers
+ *
+ * Copyright 2025 Red Hat, Inc.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef QEMU_VIRTIO_FEATURES_H
+#define QEMU_VIRTIO_FEATURES_H
+
+#include "qemu/bitops.h"
+
+#define VIRTIO_FEATURES_FMT        "%016"PRIx64"%016"PRIx64
+#define VIRTIO_FEATURES_PR(f)      (f)[1], (f)[0]
+
+#define VIRTIO_FEATURES_MAX        128
+#define VIRTIO_FEATURES_BIT(b)     BIT_ULL((b) % 64)
+#define VIRTIO_FEATURES_U64(b)     ((b) / 64)
+#define VIRTIO_FEATURES_NU32S      (VIRTIO_FEATURES_MAX / 32)
+#define VIRTIO_FEATURES_NU64S      (VIRTIO_FEATURES_MAX / 64)
+
+#define VIRTIO_DECLARE_FEATURES(name)                        \
+    union {                                                  \
+        uint64_t name;                                       \
+        uint64_t name##_ex[VIRTIO_FEATURES_NU64S];           \
+    }
+
+#define VIRTIO_DEFINE_PROP_FEATURE(_name, _state, _field, _bit, _defval)   \
+    DEFINE_PROP_BIT64(_name, _state, _field[VIRTIO_FEATURES_U64(_bit)],    \
+                      (_bit) % 64, _defval)
+
+static inline void virtio_features_clear(uint64_t *features)
+{
+    memset(features, 0, sizeof(features[0]) * VIRTIO_FEATURES_NU64S);
+}
+
+static inline void virtio_features_from_u64(uint64_t *features, uint64_t from)
+{
+    virtio_features_clear(features);
+    features[0] = from;
+}
+
+static inline bool virtio_has_feature_ex(const uint64_t *features,
+                                         unsigned int fbit)
+{
+    assert(fbit < VIRTIO_FEATURES_MAX);
+    return features[VIRTIO_FEATURES_U64(fbit)] & VIRTIO_FEATURES_BIT(fbit);
+}
+
+static inline void virtio_add_feature_ex(uint64_t *features,
+                                         unsigned int fbit)
+{
+    assert(fbit < VIRTIO_FEATURES_MAX);
+    features[VIRTIO_FEATURES_U64(fbit)] |= VIRTIO_FEATURES_BIT(fbit);
+}
+
+static inline void virtio_clear_feature_ex(uint64_t *features,
+                                           unsigned int fbit)
+{
+    assert(fbit < VIRTIO_FEATURES_MAX);
+    features[VIRTIO_FEATURES_U64(fbit)] &= ~VIRTIO_FEATURES_BIT(fbit);
+}
+
+static inline bool virtio_features_equal(const uint64_t *f1,
+                                         const uint64_t *f2)
+{
+    return !memcmp(f1, f2, sizeof(uint64_t) * VIRTIO_FEATURES_NU64S);
+}
+
+static inline bool virtio_features_use_ex(const uint64_t *features)
+{
+    int i;
+
+    for (i = 1; i < VIRTIO_FEATURES_NU64S; ++i) {
+        if (features[i]) {
+            return true;
+        }
+    }
+    return false;
+}
+
+static inline bool virtio_features_empty(const uint64_t *features)
+{
+    return !virtio_features_use_ex(features) && !features[0];
+}
+
+static inline void virtio_features_copy(uint64_t *to, const uint64_t *from)
+{
+    memcpy(to, from, sizeof(to[0]) * VIRTIO_FEATURES_NU64S);
+}
+
+static inline bool virtio_features_andnot(uint64_t *to, const uint64_t *f1,
+                                           const uint64_t *f2)
+{
+    uint64_t diff = 0;
+    int i;
+
+    for (i = 0; i < VIRTIO_FEATURES_NU64S; i++) {
+        to[i] = f1[i] & ~f2[i];
+        diff |= to[i];
+    }
+    return diff;
+}
+
+static inline void virtio_features_and(uint64_t *to, const uint64_t *f1,
+                                       const uint64_t *f2)
+{
+    int i;
+
+    for (i = 0; i < VIRTIO_FEATURES_NU64S; i++) {
+        to[i] = f1[i] & f2[i];
+    }
+}
+
+static inline void virtio_features_or(uint64_t *to, const uint64_t *f1,
+                                       const uint64_t *f2)
+{
+    int i;
+
+    for (i = 0; i < VIRTIO_FEATURES_NU64S; i++) {
+        to[i] = f1[i] | f2[i];
+    }
+}
+
+#endif
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index c594764f23..39e4059a66 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -16,6 +16,7 @@
 
 #include "system/memory.h"
 #include "hw/qdev-core.h"
+#include "hw/virtio/virtio-features.h"
 #include "net/net.h"
 #include "migration/vmstate.h"
 #include "qemu/event_notifier.h"
@@ -121,9 +122,9 @@ struct VirtIODevice
      * backend (e.g. vhost) and could potentially be a subset of the
      * total feature set offered by QEMU.
      */
-    uint64_t host_features;
-    uint64_t guest_features;
-    uint64_t backend_features;
+    VIRTIO_DECLARE_FEATURES(host_features);
+    VIRTIO_DECLARE_FEATURES(guest_features);
+    VIRTIO_DECLARE_FEATURES(backend_features);
 
     size_t config_len;
     void *config;
-- 
MST