From 2a84ffc0be7e54f2f4b76cb3ebfdde0b37bba9f0 Mon Sep 17 00:00:00 2001
From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Date: Mon, 12 Mar 2018 17:21:03 +0000
Subject: libvhost-user: Open userfaultfd
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Open a userfaultfd (on a postcopy_advise) and send it back in
the reply to the qemu for it to monitor.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 contrib/libvhost-user/libvhost-user.c | 42 +++++++++++++++++++++++++++++++++--
 contrib/libvhost-user/libvhost-user.h |  3 +++
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
index ed9f3148d3..9e31f47b7a 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -26,9 +26,20 @@
 #include <sys/socket.h>
 #include <sys/eventfd.h>
 #include <sys/mman.h>
+#include "qemu/compiler.h"
+
+#if defined(__linux__)
+#include <sys/syscall.h>
+#include <fcntl.h>
+#include <sys/ioctl.h>
 #include <linux/vhost.h>
 
-#include "qemu/compiler.h"
+#ifdef __NR_userfaultfd
+#include <linux/userfaultfd.h>
+#endif
+
+#endif
+
 #include "qemu/atomic.h"
 
 #include "libvhost-user.h"
@@ -888,8 +899,35 @@ vu_set_config(VuDev *dev, VhostUserMsg *vmsg)
 static bool
 vu_set_postcopy_advise(VuDev *dev, VhostUserMsg *vmsg)
 {
-    /* TODO: Open ufd, pass it back in the request */
+    dev->postcopy_ufd = -1;
+#ifdef UFFDIO_API
+    struct uffdio_api api_struct;
+
+    dev->postcopy_ufd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
     vmsg->size = 0;
+#endif
+
+    if (dev->postcopy_ufd == -1) {
+        vu_panic(dev, "Userfaultfd not available: %s", strerror(errno));
+        goto out;
+    }
+
+#ifdef UFFDIO_API
+    api_struct.api = UFFD_API;
+    api_struct.features = 0;
+    if (ioctl(dev->postcopy_ufd, UFFDIO_API, &api_struct)) {
+        vu_panic(dev, "Failed UFFDIO_API: %s", strerror(errno));
+        close(dev->postcopy_ufd);
+        dev->postcopy_ufd = -1;
+        goto out;
+    }
+    /* TODO: Stash feature flags somewhere */
+#endif
+
+out:
+    /* Return a ufd to the QEMU */
+    vmsg->fd_num = 1;
+    vmsg->fds[0] = dev->postcopy_ufd;
     return true; /* = send a reply */
 }
 
diff --git a/contrib/libvhost-user/libvhost-user.h b/contrib/libvhost-user/libvhost-user.h
index 00d78a8810..074b7860f6 100644
--- a/contrib/libvhost-user/libvhost-user.h
+++ b/contrib/libvhost-user/libvhost-user.h
@@ -282,6 +282,9 @@ struct VuDev {
      * re-initialize */
     vu_panic_cb panic;
     const VuDevIface *iface;
+
+    /* Postcopy data */
+    int postcopy_ufd;
 };
 
 typedef struct VuVirtqElement {
-- 
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