[Qemu-devel] [PATCH v4 02/22] vhost-user: add protocol feature negotiation

[marcandre.lureau@redhat.com]

From: "Michael S. Tsirkin" <mst@redhat.com>

Support a separate bitmask for vhost-user protocol features,
and messages to get/set protocol features.

Invoke them at init.

No features are defined yet.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 docs/specs/vhost-user.txt | 37 +++++++++++++++++++++++++++++++++
 hw/net/vhost_net.c        |  2 ++
 hw/virtio/vhost-user.c    | 52 +++++++++++++++++++++++++++++++++++++++++++++++
 include/hw/virtio/vhost.h |  1 +
 4 files changed, 92 insertions(+)

diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
index 650bb18..0062baa 100644
--- a/docs/specs/vhost-user.txt
+++ b/docs/specs/vhost-user.txt
@@ -113,6 +113,7 @@ message replies. Most of the requests don't require replies. Here is a list of
 the ones that do:
 
  * VHOST_GET_FEATURES
+ * VHOST_GET_PROTOCOL_FEATURES
  * VHOST_GET_VRING_BASE
 
 There are several messages that the master sends with file descriptors passed
@@ -127,6 +128,13 @@ in the ancillary data:
 If Master is unable to send the full message or receives a wrong reply it will
 close the connection. An optional reconnection mechanism can be implemented.
 
+Any protocol extensions are gated by protocol feature bits,
+which allows full backwards compatibility on both master
+and slave.
+As older slaves don't support negotiating protocol features,
+a feature bit was dedicated for this purpose:
+#define VHOST_USER_F_PROTOCOL_FEATURES 30
+
 Message types
 -------------
 
@@ -138,6 +146,8 @@ Message types
       Slave payload: u64
 
       Get from the underlying vhost implementation the features bitmask.
+      Feature bit VHOST_USER_F_PROTOCOL_FEATURES signals slave support for
+      VHOST_USER_GET_PROTOCOL_FEATURES and VHOST_USER_SET_PROTOCOL_FEATURES.
 
  * VHOST_USER_SET_FEATURES
 
@@ -146,6 +156,33 @@ Message types
       Master payload: u64
 
       Enable features in the underlying vhost implementation using a bitmask.
+      Feature bit VHOST_USER_F_PROTOCOL_FEATURES signals master support for
+      VHOST_USER_GET_PROTOCOL_FEATURES and VHOST_USER_SET_PROTOCOL_FEATURES.
+
+ * VHOST_USER_GET_PROTOCOL_FEATURES
+
+      Id: 15
+      Equivalent ioctl: VHOST_GET_FEATURES
+      Master payload: N/A
+      Slave payload: u64
+
+      Get the protocol feature bitmask from the underlying vhost implementation.
+      Only legal if feature bit VHOST_USER_F_PROTOCOL_FEATURES is present in
+      VHOST_USER_GET_FEATURES.
+      Note: slave that reported VHOST_USER_F_PROTOCOL_FEATURES must support
+      this message even before VHOST_USER_SET_FEATURES was called.
+
+ * VHOST_USER_SET_PROTOCOL_FEATURES
+
+      Id: 16
+      Ioctl: VHOST_SET_FEATURES
+      Master payload: u64
+
+      Enable protocol features in the underlying vhost implementation.
+      Only legal if feature bit VHOST_USER_F_PROTOCOL_FEATURES is present in
+      VHOST_USER_GET_FEATURES.
+      Note: slave that reported VHOST_USER_F_PROTOCOL_FEATURES must support
+      this message even before VHOST_USER_SET_FEATURES was called.
 
  * VHOST_USER_SET_OWNER
 
diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index 1d76b94..9d32d76 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -152,8 +152,10 @@ struct vhost_net *vhost_net_init(VhostNetOptions *options)
         net->dev.backend_features = qemu_has_vnet_hdr(options->net_backend)
             ? 0 : (1ULL << VHOST_NET_F_VIRTIO_NET_HDR);
         net->backend = r;
+        net->dev.protocol_features = 0;
     } else {
         net->dev.backend_features = 0;
+        net->dev.protocol_features = 0;
         net->backend = -1;
     }
     net->nc = options->net_backend;
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 5a83d00..de87562 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -25,6 +25,9 @@
 
 #define VHOST_MEMORY_MAX_NREGIONS    8
 
+#define VHOST_USER_F_PROTOCOL_FEATURES 30
+#define VHOST_USER_PROTOCOL_FEATURE_MASK 0x0ULL
+
 typedef enum VhostUserRequest {
     VHOST_USER_NONE = 0,
     VHOST_USER_GET_FEATURES = 1,
@@ -41,6 +44,8 @@ typedef enum VhostUserRequest {
     VHOST_USER_SET_VRING_KICK = 12,
     VHOST_USER_SET_VRING_CALL = 13,
     VHOST_USER_SET_VRING_ERR = 14,
+    VHOST_USER_GET_PROTOCOL_FEATURES = 15,
+    VHOST_USER_SET_PROTOCOL_FEATURES = 16,
     VHOST_USER_MAX
 } VhostUserRequest;
 
@@ -332,10 +337,57 @@ static int vhost_user_call(struct vhost_dev *dev, unsigned long int request,
 
 static int vhost_user_init(struct vhost_dev *dev, void *opaque)
 {
+    VhostUserMsg msg = { 0 };
+    int err;
+
     assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);
 
     dev->opaque = opaque;
 
+    msg.request = VHOST_USER_GET_FEATURES;
+    msg.flags = VHOST_USER_VERSION;
+    msg.size = 0;
+
+    err = vhost_user_write(dev, &msg, NULL, 0);
+    if (err < 0) {
+        return err;
+    }
+
+    err = vhost_user_read(dev, &msg);
+    if (err < 0) {
+        return err;
+    }
+
+    if (virtio_has_feature(msg.u64, VHOST_USER_F_PROTOCOL_FEATURES)) {
+        dev->backend_features |= 1ULL << VHOST_USER_F_PROTOCOL_FEATURES;
+
+        msg.request = VHOST_USER_GET_PROTOCOL_FEATURES;
+        msg.flags = VHOST_USER_VERSION;
+        msg.size = 0;
+
+        err = vhost_user_write(dev, &msg, NULL, 0);
+        if (err < 0) {
+            return err;
+        }
+
+        err = vhost_user_read(dev, &msg);
+        if (err < 0) {
+            return err;
+        }
+
+        dev->protocol_features = msg.u64 & VHOST_USER_PROTOCOL_FEATURE_MASK;
+
+        msg.request = VHOST_USER_SET_PROTOCOL_FEATURES;
+        msg.flags = VHOST_USER_VERSION;
+        msg.u64 = dev->protocol_features;
+        msg.size = sizeof msg.u64;
+
+        err = vhost_user_write(dev, &msg, NULL, 0);
+        if (err < 0) {
+            return err;
+        }
+    }
+
     return 0;
 }
 
diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
index dd51050..6467c73 100644
--- a/include/hw/virtio/vhost.h
+++ b/include/hw/virtio/vhost.h
@@ -47,6 +47,7 @@ struct vhost_dev {
     unsigned long long features;
     unsigned long long acked_features;
     unsigned long long backend_features;
+    unsigned long long protocol_features;
     bool started;
     bool log_enabled;
     unsigned long long log_size;
-- 
2.4.3