Some features are not always available, and virtio-net used to disable
them when not available even if the corresponding properties were
explicitly set to "on".

Convert feature properties to OnOffAuto so that the user can explicitly
tell QEMU to automatically select the value by setting them "auto".
QEMU will give an error if they are set "on".

Convert "on" to "auto" when using an old machine for compatbility.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
 include/hw/virtio/virtio-net.h |   3 +-
 hw/core/machine.c              |   1 +
 hw/net/virtio-net.c            | 254 +++++++++++++++++++++++++----------------
 3 files changed, 161 insertions(+), 97 deletions(-)

diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
index 060c23c04d2d..cfa87f739248 100644
--- a/include/hw/virtio/virtio-net.h
+++ b/include/hw/virtio/virtio-net.h
@@ -178,7 +178,7 @@ struct VirtIONet {
     uint32_t has_vnet_hdr;
     size_t host_hdr_len;
     size_t guest_hdr_len;
-    uint64_t host_features;
+    OnOffAutoBit64 host_features;
     uint32_t rsc_timeout;
     uint8_t rsc4_enabled;
     uint8_t rsc6_enabled;
@@ -218,6 +218,7 @@ struct VirtIONet {
     /* primary failover device is hidden*/
     bool failover_primary_hidden;
     bool failover;
+    bool force_features_auto;
     DeviceListener primary_listener;
     QDict *primary_opts;
     bool primary_opts_from_json;
diff --git a/hw/core/machine.c b/hw/core/machine.c
index f4cba6496c84..783d3e5695d8 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -39,6 +39,7 @@ GlobalProperty hw_compat_9_0[] = {
     {"scsi-disk-base", "migrate-emulated-scsi-request", "false" },
     {"vfio-pci", "skip-vsc-check", "false" },
     { "virtio-pci", "x-pcie-pm-no-soft-reset", "off" },
+    { TYPE_VIRTIO_NET, "x-force-features-auto", "on" },
 };
 const size_t hw_compat_9_0_len = G_N_ELEMENTS(hw_compat_9_0);
 
diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 8f3097270869..bd285921d507 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -750,58 +750,101 @@ static void virtio_net_set_queue_pairs(VirtIONet *n)
 
 static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue);
 
+static bool virtio_net_clear_features(OnOffAutoBit64 *features,
+                                      uint64_t clear_bits,
+                                      const char *reason, Error **errp)
+{
+    if (features->on_bits & clear_bits) {
+        error_setg(errp, "%s", reason);
+        return false;
+    }
+
+    features->auto_bits &= ~clear_bits;
+
+    return true;
+}
+
 static uint64_t virtio_net_get_features(VirtIODevice *vdev, uint64_t features,
                                         Error **errp)
 {
     VirtIONet *n = VIRTIO_NET(vdev);
     NetClientState *nc = qemu_get_queue(n->nic);
-
-    /* Firstly sync all virtio-net possible supported features */
-    features |= n->host_features;
-
-    virtio_add_feature(&features, VIRTIO_NET_F_MAC);
-
-    if (!peer_has_vnet_hdr(n)) {
-        virtio_clear_feature(&features, VIRTIO_NET_F_CSUM);
-        virtio_clear_feature(&features, VIRTIO_NET_F_HOST_TSO4);
-        virtio_clear_feature(&features, VIRTIO_NET_F_HOST_TSO6);
-        virtio_clear_feature(&features, VIRTIO_NET_F_HOST_ECN);
-
-        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_CSUM);
-        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_TSO4);
-        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_TSO6);
-        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_ECN);
-
-        virtio_clear_feature(&features, VIRTIO_NET_F_HOST_USO);
-        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_USO4);
-        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_USO6);
-
-        virtio_clear_feature(&features, VIRTIO_NET_F_HASH_REPORT);
-    }
-
-    if (!peer_has_vnet_hdr(n) || !peer_has_ufo(n)) {
-        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_UFO);
-        virtio_clear_feature(&features, VIRTIO_NET_F_HOST_UFO);
-    }
-
-    if (!peer_has_uso(n)) {
-        virtio_clear_feature(&features, VIRTIO_NET_F_HOST_USO);
-        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_USO4);
-        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_USO6);
+    OnOffAutoBit64 on_off_auto_features = n->host_features;
+
+    if (n->force_features_auto) {
+        on_off_auto_features.auto_bits |= on_off_auto_features.on_bits;
+        on_off_auto_features.on_bits = 0;
+    }
+
+    on_off_auto_features.on_bits |= features;
+    virtio_add_feature(&on_off_auto_features.auto_bits, VIRTIO_NET_F_MAC);
+
+    if (!((peer_has_vnet_hdr(n) ||
+           virtio_net_clear_features(&on_off_auto_features,
+                                     BIT_ULL(VIRTIO_NET_F_CSUM) |
+                                     BIT_ULL(VIRTIO_NET_F_HOST_TSO4) |
+                                     BIT_ULL(VIRTIO_NET_F_HOST_TSO6) |
+                                     BIT_ULL(VIRTIO_NET_F_HOST_ECN) |
+                                     BIT_ULL(VIRTIO_NET_F_GUEST_UFO) |
+                                     BIT_ULL(VIRTIO_NET_F_GUEST_CSUM) |
+                                     BIT_ULL(VIRTIO_NET_F_GUEST_TSO4) |
+                                     BIT_ULL(VIRTIO_NET_F_GUEST_TSO6) |
+                                     BIT_ULL(VIRTIO_NET_F_GUEST_ECN) |
+                                     BIT_ULL(VIRTIO_NET_F_HOST_UFO) |
+                                     BIT_ULL(VIRTIO_NET_F_HOST_USO) |
+                                     BIT_ULL(VIRTIO_NET_F_GUEST_USO4) |
+                                     BIT_ULL(VIRTIO_NET_F_GUEST_USO6) |
+                                     BIT_ULL(VIRTIO_NET_F_HASH_REPORT),
+                                     "A requested feature requires the peer to support virtio-net headers.",
+                                     errp)) &&
+          (peer_has_ufo(n) ||
+           virtio_net_clear_features(&on_off_auto_features,
+                                     BIT_ULL(VIRTIO_NET_F_GUEST_UFO) |
+                                     BIT_ULL(VIRTIO_NET_F_HOST_UFO),
+                                     "UFO is on but the peer does not support it.",
+                                     errp)) &&
+          (peer_has_uso(n) ||
+           virtio_net_clear_features(&on_off_auto_features,
+                                     BIT_ULL(VIRTIO_NET_F_HOST_USO) |
+                                     BIT_ULL(VIRTIO_NET_F_GUEST_USO4) |
+                                     BIT_ULL(VIRTIO_NET_F_GUEST_USO6),
+                                     "USO is on but the peer does not support it.",
+                                     errp)) &&
+          (virtio_has_feature(on_off_auto_features.on_bits |
+                              on_off_auto_features.auto_bits,
+                              VIRTIO_NET_F_CTRL_VQ) ||
+           virtio_net_clear_features(&on_off_auto_features,
+                                     BIT_ULL(VIRTIO_NET_F_GUEST_ANNOUNCE),
+                                     "guest_announce is on but ctrl_vq is off.",
+                                     errp)))) {
+        return 0;
     }
 
     if (!get_vhost_net(nc->peer)) {
-        return features;
+        if (!ebpf_rss_is_loaded(&n->ebpf_rss)) {
+            virtio_clear_feature(&on_off_auto_features.auto_bits,
+                                 VIRTIO_NET_F_RSS);
+        }
+
+        return on_off_auto_features.on_bits | on_off_auto_features.auto_bits;
     }
 
-    if (!ebpf_rss_is_loaded(&n->ebpf_rss)) {
-        virtio_clear_feature(&features, VIRTIO_NET_F_RSS);
+    if (!ebpf_rss_is_loaded(&n->ebpf_rss) &&
+        !virtio_net_clear_features(&on_off_auto_features,
+                                   BIT_ULL(VIRTIO_NET_F_RSS),
+                                   "Both RSS and vhost are on but eBPF is unavailable; fix eBPF or disable RSS.",
+                                   errp)) {
+        return 0;
     }
-    features = vhost_net_get_features(get_vhost_net(nc->peer), features);
+    features = vhost_net_get_features(get_vhost_net(nc->peer),
+                                      on_off_auto_features.on_bits |
+                                      on_off_auto_features.auto_bits);
     vdev->backend_features = features;
 
     if (n->mtu_bypass_backend &&
-            (n->host_features & 1ULL << VIRTIO_NET_F_MTU)) {
+        virtio_has_feature(on_off_auto_features.on_bits |
+                           on_off_auto_features.auto_bits,
+                           VIRTIO_NET_F_MTU)) {
         features |= (1ULL << VIRTIO_NET_F_MTU);
     }
 
@@ -820,6 +863,12 @@ static uint64_t virtio_net_get_features(VirtIODevice *vdev, uint64_t features,
         virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_ANNOUNCE);
     }
 
+    if ((features & on_off_auto_features.on_bits) !=
+        on_off_auto_features.on_bits) {
+        error_setg(errp, "A requested feature is incompatible with vhost.");
+        return 0;
+    }
+
     return features;
 }
 
@@ -3592,7 +3641,7 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
     int i;
 
     if (n->net_conf.mtu) {
-        n->host_features |= (1ULL << VIRTIO_NET_F_MTU);
+        n->host_features.on_bits |= (1ULL << VIRTIO_NET_F_MTU);
     }
 
     if (n->net_conf.duplex_str) {
@@ -3604,7 +3653,7 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
             error_setg(errp, "'duplex' must be 'half' or 'full'");
             return;
         }
-        n->host_features |= (1ULL << VIRTIO_NET_F_SPEED_DUPLEX);
+        n->host_features.on_bits |= (1ULL << VIRTIO_NET_F_SPEED_DUPLEX);
     } else {
         n->net_conf.duplex = DUPLEX_UNKNOWN;
     }
@@ -3614,7 +3663,7 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
         return;
     }
     if (n->net_conf.speed >= 0) {
-        n->host_features |= (1ULL << VIRTIO_NET_F_SPEED_DUPLEX);
+        n->host_features.on_bits |= (1ULL << VIRTIO_NET_F_SPEED_DUPLEX);
     }
 
     if (n->failover) {
@@ -3623,10 +3672,12 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
         device_listener_register(&n->primary_listener);
         migration_add_notifier(&n->migration_state,
                                virtio_net_migration_state_notifier);
-        n->host_features |= (1ULL << VIRTIO_NET_F_STANDBY);
+        n->host_features.on_bits |= (1ULL << VIRTIO_NET_F_STANDBY);
     }
 
-    virtio_net_set_config_size(n, n->host_features);
+    virtio_net_set_config_size(n,
+                               n->host_features.on_bits |
+                               n->host_features.auto_bits);
     virtio_init(vdev, VIRTIO_ID_NET, n->config_size);
 
     /*
@@ -3753,7 +3804,9 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
 
     net_rx_pkt_init(&n->rx_pkt);
 
-    if (virtio_has_feature(n->host_features, VIRTIO_NET_F_RSS)) {
+    if (virtio_has_feature(n->host_features.on_bits |
+                           n->host_features.auto_bits,
+                           VIRTIO_NET_F_RSS)) {
         virtio_net_load_ebpf(n);
     }
 }
@@ -3764,7 +3817,9 @@ static void virtio_net_device_unrealize(DeviceState *dev)
     VirtIONet *n = VIRTIO_NET(dev);
     int i, max_queue_pairs;
 
-    if (virtio_has_feature(n->host_features, VIRTIO_NET_F_RSS)) {
+    if (virtio_has_feature(n->host_features.on_bits |
+                           n->host_features.auto_bits,
+                           VIRTIO_NET_F_RSS)) {
         virtio_net_unload_ebpf(n);
     }
 
@@ -3908,53 +3963,58 @@ static const VMStateDescription vmstate_virtio_net = {
 };
 
 static Property virtio_net_properties[] = {
-    DEFINE_PROP_BIT64("csum", VirtIONet, host_features,
-                    VIRTIO_NET_F_CSUM, true),
-    DEFINE_PROP_BIT64("guest_csum", VirtIONet, host_features,
-                    VIRTIO_NET_F_GUEST_CSUM, true),
-    DEFINE_PROP_BIT64("gso", VirtIONet, host_features, VIRTIO_NET_F_GSO, true),
-    DEFINE_PROP_BIT64("guest_tso4", VirtIONet, host_features,
-                    VIRTIO_NET_F_GUEST_TSO4, true),
-    DEFINE_PROP_BIT64("guest_tso6", VirtIONet, host_features,
-                    VIRTIO_NET_F_GUEST_TSO6, true),
-    DEFINE_PROP_BIT64("guest_ecn", VirtIONet, host_features,
-                    VIRTIO_NET_F_GUEST_ECN, true),
-    DEFINE_PROP_BIT64("guest_ufo", VirtIONet, host_features,
-                    VIRTIO_NET_F_GUEST_UFO, true),
-    DEFINE_PROP_BIT64("guest_announce", VirtIONet, host_features,
-                    VIRTIO_NET_F_GUEST_ANNOUNCE, true),
-    DEFINE_PROP_BIT64("host_tso4", VirtIONet, host_features,
-                    VIRTIO_NET_F_HOST_TSO4, true),
-    DEFINE_PROP_BIT64("host_tso6", VirtIONet, host_features,
-                    VIRTIO_NET_F_HOST_TSO6, true),
-    DEFINE_PROP_BIT64("host_ecn", VirtIONet, host_features,
-                    VIRTIO_NET_F_HOST_ECN, true),
-    DEFINE_PROP_BIT64("host_ufo", VirtIONet, host_features,
-                    VIRTIO_NET_F_HOST_UFO, true),
-    DEFINE_PROP_BIT64("mrg_rxbuf", VirtIONet, host_features,
-                    VIRTIO_NET_F_MRG_RXBUF, true),
-    DEFINE_PROP_BIT64("status", VirtIONet, host_features,
-                    VIRTIO_NET_F_STATUS, true),
-    DEFINE_PROP_BIT64("ctrl_vq", VirtIONet, host_features,
-                    VIRTIO_NET_F_CTRL_VQ, true),
-    DEFINE_PROP_BIT64("ctrl_rx", VirtIONet, host_features,
-                    VIRTIO_NET_F_CTRL_RX, true),
-    DEFINE_PROP_BIT64("ctrl_vlan", VirtIONet, host_features,
-                    VIRTIO_NET_F_CTRL_VLAN, true),
-    DEFINE_PROP_BIT64("ctrl_rx_extra", VirtIONet, host_features,
-                    VIRTIO_NET_F_CTRL_RX_EXTRA, true),
-    DEFINE_PROP_BIT64("ctrl_mac_addr", VirtIONet, host_features,
-                    VIRTIO_NET_F_CTRL_MAC_ADDR, true),
-    DEFINE_PROP_BIT64("ctrl_guest_offloads", VirtIONet, host_features,
-                    VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, true),
-    DEFINE_PROP_BIT64("mq", VirtIONet, host_features, VIRTIO_NET_F_MQ, false),
-    DEFINE_PROP_BIT64("rss", VirtIONet, host_features,
-                    VIRTIO_NET_F_RSS, false),
-    DEFINE_PROP_BIT64("hash", VirtIONet, host_features,
-                    VIRTIO_NET_F_HASH_REPORT, false),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("csum", VirtIONet, host_features,
+                                  VIRTIO_NET_F_CSUM, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("guest_csum", VirtIONet, host_features,
+                                  VIRTIO_NET_F_GUEST_CSUM, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("gso", VirtIONet, host_features,
+                                  VIRTIO_NET_F_GSO, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("guest_tso4", VirtIONet, host_features,
+                                  VIRTIO_NET_F_GUEST_TSO4, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("guest_tso6", VirtIONet, host_features,
+                                  VIRTIO_NET_F_GUEST_TSO6, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("guest_ecn", VirtIONet, host_features,
+                                  VIRTIO_NET_F_GUEST_ECN, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("guest_ufo", VirtIONet, host_features,
+                                  VIRTIO_NET_F_GUEST_UFO, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("guest_announce", VirtIONet, host_features,
+                                  VIRTIO_NET_F_GUEST_ANNOUNCE,
+                                  ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("host_tso4", VirtIONet, host_features,
+                                  VIRTIO_NET_F_HOST_TSO4, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("host_tso6", VirtIONet, host_features,
+                                  VIRTIO_NET_F_HOST_TSO6, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("host_ecn", VirtIONet, host_features,
+                                  VIRTIO_NET_F_HOST_ECN, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("host_ufo", VirtIONet, host_features,
+                                  VIRTIO_NET_F_HOST_UFO, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("mrg_rxbuf", VirtIONet, host_features,
+                                  VIRTIO_NET_F_MRG_RXBUF, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("status", VirtIONet, host_features,
+                                  VIRTIO_NET_F_STATUS, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("ctrl_vq", VirtIONet, host_features,
+                                  VIRTIO_NET_F_CTRL_VQ, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("ctrl_rx", VirtIONet, host_features,
+                                  VIRTIO_NET_F_CTRL_RX, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("ctrl_vlan", VirtIONet, host_features,
+                                  VIRTIO_NET_F_CTRL_VLAN, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("ctrl_rx_extra", VirtIONet, host_features,
+                                  VIRTIO_NET_F_CTRL_RX_EXTRA, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("ctrl_mac_addr", VirtIONet, host_features,
+                                  VIRTIO_NET_F_CTRL_MAC_ADDR, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("ctrl_guest_offloads", VirtIONet,
+                                  host_features,
+                                  VIRTIO_NET_F_CTRL_GUEST_OFFLOADS,
+                                  ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("mq", VirtIONet, host_features,
+                                  VIRTIO_NET_F_MQ, ON_OFF_AUTO_OFF),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("rss", VirtIONet, host_features,
+                                  VIRTIO_NET_F_RSS, ON_OFF_AUTO_OFF),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("hash", VirtIONet, host_features,
+                                  VIRTIO_NET_F_HASH_REPORT, ON_OFF_AUTO_OFF),
     DEFINE_PROP_ARRAY("ebpf-rss-fds", VirtIONet, nr_ebpf_rss_fds,
                       ebpf_rss_fds, qdev_prop_string, char*),
-    DEFINE_PROP_BIT64("guest_rsc_ext", VirtIONet, host_features,
+    DEFINE_PROP_BIT64("guest_rsc_ext", VirtIONet, host_features.on_bits,
                     VIRTIO_NET_F_RSC_EXT, false),
     DEFINE_PROP_UINT32("rsc_interval", VirtIONet, rsc_timeout,
                        VIRTIO_NET_RSC_DEFAULT_INTERVAL),
@@ -3973,12 +4033,14 @@ static Property virtio_net_properties[] = {
     DEFINE_PROP_INT32("speed", VirtIONet, net_conf.speed, SPEED_UNKNOWN),
     DEFINE_PROP_STRING("duplex", VirtIONet, net_conf.duplex_str),
     DEFINE_PROP_BOOL("failover", VirtIONet, failover, false),
-    DEFINE_PROP_BIT64("guest_uso4", VirtIONet, host_features,
-                      VIRTIO_NET_F_GUEST_USO4, true),
-    DEFINE_PROP_BIT64("guest_uso6", VirtIONet, host_features,
-                      VIRTIO_NET_F_GUEST_USO6, true),
-    DEFINE_PROP_BIT64("host_uso", VirtIONet, host_features,
-                      VIRTIO_NET_F_HOST_USO, true),
+    DEFINE_PROP_BOOL("x-force-features-auto", VirtIONet, force_features_auto,
+                     false),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("guest_uso4", VirtIONet, host_features,
+                                  VIRTIO_NET_F_GUEST_USO4, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("guest_uso6", VirtIONet, host_features,
+                                  VIRTIO_NET_F_GUEST_USO6, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO_BIT64("host_uso", VirtIONet, host_features,
+                                  VIRTIO_NET_F_HOST_USO, ON_OFF_AUTO_AUTO),
     DEFINE_PROP_END_OF_LIST(),
 };
 

-- 
2.45.2