From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Register the UFD that comes in as the response to the 'advise' method
with the postcopy code.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 hw/virtio/vhost-user.c   | 23 ++++++++++++++++++++++-
 migration/postcopy-ram.h |  2 +-
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index ee9a1ac8a3..b98fbe4834 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -24,6 +24,7 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <linux/vhost.h>
+#include <linux/userfaultfd.h>
 
 #define VHOST_MEMORY_MAX_NREGIONS    8
 #define VHOST_USER_F_PROTOCOL_FEATURES 30
@@ -128,6 +129,7 @@ struct vhost_user {
     CharBackend *chr;
     int slave_fd;
     NotifierWithReturn postcopy_notifier;
+    struct PostCopyFD  postcopy_fd;
 };
 
 static bool ioeventfd_enabled(void)
@@ -707,6 +709,19 @@ out:
 }
 
 /*
+ * Called back from the postcopy fault thread when a fault is received on our
+ * ufd.
+ * TODO: This is Linux specific
+ */
+static int vhost_user_postcopy_fault_handler(struct PostCopyFD *pcfd,
+                                             void *ufd)
+{
+    struct uffd_msg *msg = ufd;
+
+    return 0;
+}
+
+/*
  * Called at the start of an inbound postcopy on reception of the
  * 'advise' command.
  */
@@ -745,8 +760,14 @@ static int vhost_user_postcopy_advise(struct vhost_dev *dev, Error **errp)
         error_setg(errp, "%s: Failed to get ufd", __func__);
         return -1;
     }
+    fcntl(ufd, F_SETFL, O_NONBLOCK);
 
-    /* TODO: register ufd with userfault thread */
+    /* register ufd with userfault thread */
+    u->postcopy_fd.fd = ufd;
+    u->postcopy_fd.data = dev;
+    u->postcopy_fd.handler = vhost_user_postcopy_fault_handler;
+    u->postcopy_fd.idstr = "vhost-user"; /* Need to find unique name */
+    postcopy_register_shared_ufd(&u->postcopy_fd);
     return 0;
 }
 
diff --git a/migration/postcopy-ram.h b/migration/postcopy-ram.h
index ba8a8ffec5..28c216cc7a 100644
--- a/migration/postcopy-ram.h
+++ b/migration/postcopy-ram.h
@@ -153,7 +153,7 @@ struct PostCopyFD {
     /* Handler to be called whenever we get a poll event */
     pcfdhandler handler;
     /* A string to use in error messages */
-    char *idstr;
+    const char *idstr;
 };
 
 /* Register a userfaultfd owned by an external process for
-- 
2.13.0