diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c
index e4679c73ab..2e7f4b786d 100644
--- a/tools/virtiofsd/fuse_lowlevel.c
+++ b/tools/virtiofsd/fuse_lowlevel.c
@@ -179,8 +179,8 @@ int fuse_send_reply_iov_nofree(fuse_req_t req, int error, struct iovec *iov,
         .unique = req->unique,
         .error = error,
     };
-
-    if (error <= -1000 || error > 0) {
+    /* error = 1 has been used to signal client to wait for notificaiton */
+    if (error <= -1000 || error > 1) {
         fuse_log(FUSE_LOG_ERR, "fuse: bad error value: %i\n", error);
         out.error = -ERANGE;
     }
@@ -290,6 +290,11 @@ int fuse_reply_err(fuse_req_t req, int err)
     return send_reply(req, -err, NULL, 0);
 }
 
+int fuse_reply_wait(fuse_req_t req)
+{
+    return send_reply(req, 1, NULL, 0);
+}
+
 void fuse_reply_none(fuse_req_t req)
 {
     fuse_free_req(req);
@@ -2165,6 +2170,34 @@ static void do_destroy(fuse_req_t req, fuse_ino_t nodeid,
     send_reply_ok(req, NULL, 0);
 }
 
+static int send_notify_iov(struct fuse_session *se, int notify_code,
+                           struct iovec *iov, int count)
+{
+    struct fuse_out_header out;
+    if (!se->got_init) {
+        return -ENOTCONN;
+    }
+    out.unique = 0;
+    out.error = notify_code;
+    iov[0].iov_base = &out;
+    iov[0].iov_len = sizeof(struct fuse_out_header);
+    return fuse_send_msg(se, NULL, iov, count);
+}
+
+int fuse_lowlevel_notify_lock(struct fuse_session *se, uint64_t unique,
+                  int32_t error)
+{
+    struct fuse_notify_lock_out outarg = {0};
+    struct iovec iov[2];
+
+    outarg.unique = unique;
+    outarg.error = -error;
+
+    iov[1].iov_base = &outarg;
+    iov[1].iov_len = sizeof(outarg);
+    return send_notify_iov(se, FUSE_NOTIFY_LOCK, iov, 2);
+}
+
 int fuse_lowlevel_notify_store(struct fuse_session *se, fuse_ino_t ino,
                                off_t offset, struct fuse_bufvec *bufv)
 {
diff --git a/tools/virtiofsd/fuse_lowlevel.h b/tools/virtiofsd/fuse_lowlevel.h
index c55c0ca2fc..64624b48dc 100644
--- a/tools/virtiofsd/fuse_lowlevel.h
+++ b/tools/virtiofsd/fuse_lowlevel.h
@@ -1251,6 +1251,22 @@ struct fuse_lowlevel_ops {
  */
 int fuse_reply_err(fuse_req_t req, int err);
 
+/**
+ * Ask caller to wait for lock.
+ *
+ * Possible requests:
+ *   setlkw
+ *
+ * If caller sends a blocking lock request (setlkw), then reply to caller
+ * that wait for lock to be available. Once lock is available caller will
+ * receive a notification with request's unique id. Notification will
+ * carry info whether lock was successfully obtained or not.
+ *
+ * @param req request handle
+ * @return zero for success, -errno for failure to send reply
+ */
+int fuse_reply_wait(fuse_req_t req);
+
 /**
  * Don't send reply
  *
@@ -1685,6 +1701,16 @@ int fuse_lowlevel_notify_delete(struct fuse_session *se, fuse_ino_t parent,
 int fuse_lowlevel_notify_store(struct fuse_session *se, fuse_ino_t ino,
                                off_t offset, struct fuse_bufvec *bufv);
 
+/**
+ * Notify event related to previous lock request
+ *
+ * @param se the session object
+ * @param unique the unique id of the request which requested setlkw
+ * @param error zero for success, -errno for the failure
+ */
+int fuse_lowlevel_notify_lock(struct fuse_session *se, uint64_t unique,
+                              int32_t error);
+
 /*
  * Utility functions
  */
diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c
index a87e88e286..bb2d4456fc 100644
--- a/tools/virtiofsd/fuse_virtio.c
+++ b/tools/virtiofsd/fuse_virtio.c
@@ -273,6 +273,23 @@ static void vq_send_element(struct fv_QueueInfo *qi, VuVirtqElement *elem,
     vu_dispatch_unlock(qi->virtio_dev);
 }
 
+/* Returns NULL if queue is empty */
+static FVRequest *vq_pop_notify_elem(struct fv_QueueInfo *qi)
+{
+    struct fuse_session *se = qi->virtio_dev->se;
+    VuDev *dev = &se->virtio_dev->dev;
+    VuVirtq *q = vu_get_queue(dev, qi->qidx);
+    FVRequest *req;
+
+    vu_dispatch_rdlock(qi->virtio_dev);
+    pthread_mutex_lock(&qi->vq_lock);
+    /* Pop an element from queue */
+    req = vu_queue_pop(dev, q, sizeof(FVRequest));
+    pthread_mutex_unlock(&qi->vq_lock);
+    vu_dispatch_unlock(qi->virtio_dev);
+    return req;
+}
+
 /*
  * Called back by ll whenever it wants to send a reply/message back
  * The 1st element of the iov starts with the fuse_out_header
@@ -281,9 +298,9 @@ static void vq_send_element(struct fv_QueueInfo *qi, VuVirtqElement *elem,
 int virtio_send_msg(struct fuse_session *se, struct fuse_chan *ch,
                     struct iovec *iov, int count)
 {
-    FVRequest *req = container_of(ch, FVRequest, ch);
-    struct fv_QueueInfo *qi = ch->qi;
-    VuVirtqElement *elem = &req->elem;
+    FVRequest *req;
+    struct fv_QueueInfo *qi;
+    VuVirtqElement *elem;
     int ret = 0;
 
     assert(count >= 1);
@@ -294,8 +311,30 @@ int virtio_send_msg(struct fuse_session *se, struct fuse_chan *ch,
 
     size_t tosend_len = iov_size(iov, count);
 
-    /* unique == 0 is notification, which we don't support */
-    assert(out->unique);
+    /* unique == 0 is notification */
+    if (!out->unique) {
+        if (!se->notify_enabled) {
+            return -EOPNOTSUPP;
+        }
+        /* If notifications are enabled, queue index 1 is notification queue */
+        qi = se->virtio_dev->qi[1];
+        req = vq_pop_notify_elem(qi);
+        if (!req) {
+            /*
+             * TODO: Implement some sort of ring buffer and queue notifications
+             * on that and send these later when notification queue has space
+             * available.
+             */
+            return -ENOSPC;
+        }
+        req->reply_sent = false;
+    } else {
+        assert(ch);
+        req = container_of(ch, FVRequest, ch);
+        qi = ch->qi;
+    }
+
+    elem = &req->elem;
     assert(!req->reply_sent);
 
     /* The 'in' part of the elem is to qemu */
@@ -985,6 +1024,7 @@ static int fv_get_config(VuDev *dev, uint8_t *config, uint32_t len)
         struct fuse_notify_delete_out       delete_out;
         struct fuse_notify_store_out        store_out;
         struct fuse_notify_retrieve_out     retrieve_out;
+        struct fuse_notify_lock_out         lock_out;
     };
 
     notify_size = sizeof(struct fuse_out_header) +
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index 6928662e22..277f74762b 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -2131,13 +2131,35 @@ out:
     }
 }
 
+static void setlk_send_notification(struct fuse_session *se, uint64_t unique,
+                                    int saverr)
+{
+    int ret;
+
+    do {
+        ret = fuse_lowlevel_notify_lock(se, unique, saverr);
+        /*
+         * Retry sending notification if notification queue does not have
+         * free descriptor yet, otherwise break out of loop. Either we
+         * successfully sent notifiation or some other error occurred.
+         */
+        if (ret != -ENOSPC) {
+            break;
+        }
+        usleep(10000);
+    } while (1);
+}
+
 static void lo_setlk(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi,
                      struct flock *lock, int sleep)
 {
     struct lo_data *lo = lo_data(req);
     struct lo_inode *inode;
     struct lo_inode_plock *plock;
-    int ret, saverr = 0;
+    int ret, saverr = 0, ofd;
+    uint64_t unique;
+    struct fuse_session *se = req->se;
+    bool blocking_lock = false;
 
     fuse_log(FUSE_LOG_DEBUG,
              "lo_setlk(ino=%" PRIu64 ", flags=%d)"
@@ -2151,11 +2173,6 @@ static void lo_setlk(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi,
         return;
     }
 
-    if (sleep) {
-        fuse_reply_err(req, EOPNOTSUPP);
-        return;
-    }
-
     inode = lo_inode(req, ino);
     if (!inode) {
         fuse_reply_err(req, EBADF);
@@ -2168,21 +2185,56 @@ static void lo_setlk(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi,
 
     if (!plock) {
         saverr = ret;
+        pthread_mutex_unlock(&inode->plock_mutex);
         goto out;
     }
 
+    /*
+     * plock is now released when inode is going away. We already have
+     * a reference on inode, so it is guaranteed that plock->fd is
+     * still around even after dropping inode->plock_mutex lock
+     */
+    ofd = plock->fd;
+    pthread_mutex_unlock(&inode->plock_mutex);
+
+    /*
+     * If this lock request can block, request caller to wait for
+     * notification. Do not access req after this. Once lock is
+     * available, send a notification instead.
+     */
+    if (sleep && lock->l_type != F_UNLCK) {
+        /*
+         * If notification queue is not enabled, can't support async
+         * locks.
+         */
+        if (!se->notify_enabled) {
+            saverr = EOPNOTSUPP;
+            goto out;
+        }
+        blocking_lock = true;
+        unique = req->unique;
+        fuse_reply_wait(req);
+    }
+
     /* TODO: Is it alright to modify flock? */
     lock->l_pid = 0;
-    ret = fcntl(plock->fd, F_OFD_SETLK, lock);
+    if (blocking_lock) {
+        ret = fcntl(ofd, F_OFD_SETLKW, lock);
+    } else {
+        ret = fcntl(ofd, F_OFD_SETLK, lock);
+    }
     if (ret == -1) {
         saverr = errno;
     }
 
 out:
-    pthread_mutex_unlock(&inode->plock_mutex);
     lo_inode_put(lo, &inode);
 
-    fuse_reply_err(req, saverr);
+    if (!blocking_lock) {
+        fuse_reply_err(req, saverr);
+    } else {
+        setlk_send_notification(se, unique, saverr);
+    }
 }
 
 static void lo_fsyncdir(fuse_req_t req, fuse_ino_t ino, int datasync,
