[PATCH v5 6/6] libvhost-user: implement in-band notifications

[Johannes Berg <johannes@sipsolutions.net>]

From: Johannes Berg <johannes.berg@intel.com>

Add support for VHOST_USER_PROTOCOL_F_IN_BAND_NOTIFICATIONS, but
as it's not desired by default, don't enable it unless the device
implementation opts in by returning it from its protocol features
callback.

Note that I updated vu_set_vring_err_exec(), but didn't add any
sending of the VHOST_USER_SLAVE_VRING_ERR message as there's no
write to the err_fd today either.

This also adds vu_queue_notify_sync() which can be used to force
a synchronous notification if inband notifications are supported.
Previously, I had left out the slave->master direction handling
of F_REPLY_ACK, this now adds some code to support it as well.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 contrib/libvhost-user/libvhost-user.c | 103 +++++++++++++++++++++++++-
 contrib/libvhost-user/libvhost-user.h |  14 ++++
 2 files changed, 114 insertions(+), 3 deletions(-)

diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
index 34d08e2fc4be..5cb8e6e32158 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -136,6 +136,7 @@ vu_request_to_string(unsigned int req)
         REQ(VHOST_USER_GET_INFLIGHT_FD),
         REQ(VHOST_USER_SET_INFLIGHT_FD),
         REQ(VHOST_USER_GPU_SET_SOCKET),
+        REQ(VHOST_USER_VRING_KICK),
         REQ(VHOST_USER_MAX),
     };
 #undef REQ
@@ -163,7 +164,10 @@ vu_panic(VuDev *dev, const char *msg, ...)
     dev->panic(dev, buf);
     free(buf);
 
-    /* FIXME: find a way to call virtio_error? */
+    /*
+     * FIXME:
+     * find a way to call virtio_error, or perhaps close the connection?
+     */
 }
 
 /* Translate guest physical address to our virtual address.  */
@@ -1172,6 +1176,14 @@ vu_set_vring_err_exec(VuDev *dev, VhostUserMsg *vmsg)
 static bool
 vu_get_protocol_features_exec(VuDev *dev, VhostUserMsg *vmsg)
 {
+    /*
+     * Note that we support, but intentionally do not set,
+     * VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS. This means that
+     * a device implementation can return it in its callback
+     * (get_protocol_features) if it wants to use this for
+     * simulation, but it is otherwise not desirable (if even
+     * implemented by the master.)
+     */
     uint64_t features = 1ULL << VHOST_USER_PROTOCOL_F_MQ |
                         1ULL << VHOST_USER_PROTOCOL_F_LOG_SHMFD |
                         1ULL << VHOST_USER_PROTOCOL_F_SLAVE_REQ |
@@ -1204,6 +1216,25 @@ vu_set_protocol_features_exec(VuDev *dev, VhostUserMsg *vmsg)
 
     dev->protocol_features = vmsg->payload.u64;
 
+    if (vu_has_protocol_feature(dev,
+                                VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS) &&
+        (!vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_SLAVE_REQ) ||
+         !vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_REPLY_ACK))) {
+        /*
+         * The use case for using messages for kick/call is simulation, to make
+         * the kick and call synchronous. To actually get that behaviour, both
+         * of the other features are required.
+         * Theoretically, one could use only kick messages, or do them without
+         * having F_REPLY_ACK, but too many (possibly pending) messages on the
+         * socket will eventually cause the master to hang, to avoid this in
+         * scenarios where not desired enforce that the settings are in a way
+         * that actually enables the simulation case.
+         */
+        vu_panic(dev,
+                 "F_IN_BAND_NOTIFICATIONS requires F_SLAVE_REQ && F_REPLY_ACK");
+        return false;
+    }
+
     if (dev->iface->set_protocol_features) {
         dev->iface->set_protocol_features(dev, features);
     }
@@ -1464,6 +1495,34 @@ vu_set_inflight_fd(VuDev *dev, VhostUserMsg *vmsg)
     return false;
 }
 
+static bool
+vu_handle_vring_kick(VuDev *dev, VhostUserMsg *vmsg)
+{
+    unsigned int index = vmsg->payload.state.index;
+
+    if (index >= dev->max_queues) {
+        vu_panic(dev, "Invalid queue index: %u", index);
+        return false;
+    }
+
+    DPRINT("Got kick message: handler:%p idx:%d\n",
+           dev->vq[index].handler, index);
+
+    if (!dev->vq[index].started) {
+        dev->vq[index].started = true;
+
+        if (dev->iface->queue_set_started) {
+            dev->iface->queue_set_started(dev, index, true);
+        }
+    }
+
+    if (dev->vq[index].handler) {
+        dev->vq[index].handler(dev, index);
+    }
+
+    return false;
+}
+
 static bool
 vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
 {
@@ -1546,6 +1605,8 @@ vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
         return vu_get_inflight_fd(dev, vmsg);
     case VHOST_USER_SET_INFLIGHT_FD:
         return vu_set_inflight_fd(dev, vmsg);
+    case VHOST_USER_VRING_KICK:
+        return vu_handle_vring_kick(dev, vmsg);
     default:
         vmsg_close_fds(vmsg);
         vu_panic(dev, "Unhandled request: %d", vmsg->request);
@@ -2005,8 +2066,7 @@ vring_notify(VuDev *dev, VuVirtq *vq)
     return !v || vring_need_event(vring_get_used_event(vq), new, old);
 }
 
-void
-vu_queue_notify(VuDev *dev, VuVirtq *vq)
+static void _vu_queue_notify(VuDev *dev, VuVirtq *vq, bool sync)
 {
     if (unlikely(dev->broken) ||
         unlikely(!vq->vring.avail)) {
@@ -2018,11 +2078,48 @@ vu_queue_notify(VuDev *dev, VuVirtq *vq)
         return;
     }
 
+    if (vq->call_fd < 0 &&
+        vu_has_protocol_feature(dev,
+                                VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS) &&
+        vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_SLAVE_REQ)) {
+        VhostUserMsg vmsg = {
+            .request = VHOST_USER_SLAVE_VRING_CALL,
+            .flags = VHOST_USER_VERSION,
+            .size = sizeof(vmsg.payload.state),
+            .payload.state = {
+                .index = vq - dev->vq,
+            },
+        };
+        bool ack = sync &&
+                   vu_has_protocol_feature(dev,
+                                           VHOST_USER_PROTOCOL_F_REPLY_ACK);
+
+        if (ack) {
+            vmsg.flags |= VHOST_USER_NEED_REPLY_MASK;
+        }
+
+        vu_message_write(dev, dev->slave_fd, &vmsg);
+        if (ack) {
+            vu_message_read(dev, dev->slave_fd, &vmsg);
+        }
+        return;
+    }
+
     if (eventfd_write(vq->call_fd, 1) < 0) {
         vu_panic(dev, "Error writing eventfd: %s", strerror(errno));
     }
 }
 
+void vu_queue_notify(VuDev *dev, VuVirtq *vq)
+{
+    _vu_queue_notify(dev, vq, false);
+}
+
+void vu_queue_notify_sync(VuDev *dev, VuVirtq *vq)
+{
+    _vu_queue_notify(dev, vq, true);
+}
+
 static inline void
 vring_used_flags_set_bit(VuVirtq *vq, int mask)
 {
diff --git a/contrib/libvhost-user/libvhost-user.h b/contrib/libvhost-user/libvhost-user.h
index 46b600799b2e..cd12cbd92cc5 100644
--- a/contrib/libvhost-user/libvhost-user.h
+++ b/contrib/libvhost-user/libvhost-user.h
@@ -53,6 +53,7 @@ enum VhostUserProtocolFeature {
     VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD = 10,
     VHOST_USER_PROTOCOL_F_HOST_NOTIFIER = 11,
     VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD = 12,
+    VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS = 14,
 
     VHOST_USER_PROTOCOL_F_MAX
 };
@@ -94,6 +95,7 @@ typedef enum VhostUserRequest {
     VHOST_USER_GET_INFLIGHT_FD = 31,
     VHOST_USER_SET_INFLIGHT_FD = 32,
     VHOST_USER_GPU_SET_SOCKET = 33,
+    VHOST_USER_VRING_KICK = 35,
     VHOST_USER_MAX
 } VhostUserRequest;
 
@@ -102,6 +104,8 @@ typedef enum VhostUserSlaveRequest {
     VHOST_USER_SLAVE_IOTLB_MSG = 1,
     VHOST_USER_SLAVE_CONFIG_CHANGE_MSG = 2,
     VHOST_USER_SLAVE_VRING_HOST_NOTIFIER_MSG = 3,
+    VHOST_USER_SLAVE_VRING_CALL = 4,
+    VHOST_USER_SLAVE_VRING_ERR = 5,
     VHOST_USER_SLAVE_MAX
 }  VhostUserSlaveRequest;
 
@@ -522,6 +526,16 @@ bool vu_queue_empty(VuDev *dev, VuVirtq *vq);
  */
 void vu_queue_notify(VuDev *dev, VuVirtq *vq);
 
+/**
+ * vu_queue_notify_sync:
+ * @dev: a VuDev context
+ * @vq: a VuVirtq queue
+ *
+ * Request to notify the queue via callfd (skipped if unnecessary)
+ * or sync message if possible.
+ */
+void vu_queue_notify_sync(VuDev *dev, VuVirtq *vq);
+
 /**
  * vu_queue_pop:
  * @dev: a VuDev context
-- 
2.24.1