3 files changed, 56 insertions, 12 deletions

diff --git a/drivers/hv/hv_snapshot.c b/drivers/hv/hv_snapshot.c
index 2c8c246d09eb..ee1762b39bf2 100644
--- a/drivers/hv/hv_snapshot.c
+++ b/drivers/hv/hv_snapshot.c
@@ -59,6 +59,11 @@ static struct {
 
 static void vss_respond_to_host(int error);
 
+/*
+ * This state maintains the version number registered by the daemon.
+ */
+static int dm_reg_value;
+
 static const char vss_devname[] = "vmbus/hv_vss";
 static __u8 *recv_buffer;
 static struct hvutil_transport *hvt;
@@ -89,6 +94,29 @@ static void vss_timeout_func(struct work_struct *dummy)
                         hv_vss_onchannelcallback);
 }
 
+static int vss_handle_handshake(struct hv_vss_msg *vss_msg)
+{
+        u32 our_ver = VSS_OP_REGISTER1;
+
+        switch (vss_msg->vss_hdr.operation) {
+        case VSS_OP_REGISTER:
+                /* Daemon doesn't expect us to reply */
+                dm_reg_value = VSS_OP_REGISTER;
+                break;
+        case VSS_OP_REGISTER1:
+                /* Daemon expects us to reply with our own version*/
+                if (hvutil_transport_send(hvt, &our_ver, sizeof(our_ver)))
+                        return -EFAULT;
+                dm_reg_value = VSS_OP_REGISTER1;
+                break;
+        default:
+                return -EINVAL;
+        }
+        vss_transaction.state = HVUTIL_READY;
+        pr_info("VSS daemon registered\n");
+        return 0;
+}
+
 static int vss_on_msg(void *msg, int len)
 {
         struct hv_vss_msg *vss_msg = (struct hv_vss_msg *)msg;
@@ -96,18 +124,15 @@ static int vss_on_msg(void *msg, int len)
         if (len != sizeof(*vss_msg))
                 return -EINVAL;
 
-        /*
-         * Don't process registration messages if we're in the middle of
-         * a transaction processing.
-         */
-        if (vss_transaction.state > HVUTIL_READY &&
-            vss_msg->vss_hdr.operation == VSS_OP_REGISTER)
-                return -EINVAL;
-
-        if (vss_transaction.state == HVUTIL_DEVICE_INIT &&
-            vss_msg->vss_hdr.operation == VSS_OP_REGISTER) {
-                pr_info("VSS daemon registered\n");
-                vss_transaction.state = HVUTIL_READY;
+        if (vss_msg->vss_hdr.operation == VSS_OP_REGISTER ||
+            vss_msg->vss_hdr.operation == VSS_OP_REGISTER1) {
+                /*
+                 * Don't process registration messages if we're in the middle
+                 * of a transaction processing.
+                 */
+                if (vss_transaction.state > HVUTIL_READY)
+                        return -EINVAL;
+                return vss_handle_handshake(vss_msg);
         } else if (vss_transaction.state == HVUTIL_USERSPACE_REQ) {
                 vss_transaction.state = HVUTIL_USERSPACE_RECV;
                 if (cancel_delayed_work_sync(&vss_timeout_work)) {
diff --git a/include/uapi/linux/hyperv.h b/include/uapi/linux/hyperv.h
index bb1cb73c927a..66c76df2c32d 100644
--- a/include/uapi/linux/hyperv.h
+++ b/include/uapi/linux/hyperv.h
@@ -45,6 +45,11 @@
 
 #define VSS_OP_REGISTER 128
 
+/*
+  Daemon code with full handshake support.
+ */
+#define VSS_OP_REGISTER1 129
+
 enum hv_vss_op {
         VSS_OP_CREATE = 0,
         VSS_OP_DELETE,
diff --git a/tools/hv/hv_vss_daemon.c b/tools/hv/hv_vss_daemon.c
index 36f18211afa7..96234b638249 100644
--- a/tools/hv/hv_vss_daemon.c
+++ b/tools/hv/hv_vss_daemon.c
@@ -148,6 +148,8 @@ int main(int argc, char *argv[])
         int     op;
         struct hv_vss_msg vss_msg[1];
         int daemonize = 1, long_index = 0, opt;
+        int in_handshake = 1;
+        __u32 kernel_modver;
 
         static struct option long_options[] = {
                 {"help",        no_argument,       0,  'h' },
@@ -211,6 +213,18 @@ int main(int argc, char *argv[])
 
                 len = read(vss_fd, vss_msg, sizeof(struct hv_vss_msg));
 
+                if (in_handshake) {
+                        if (len != sizeof(kernel_modver)) {
+                                syslog(LOG_ERR, "invalid version negotiation");
+                                exit(EXIT_FAILURE);
+                        }
+                        kernel_modver = *(__u32 *)vss_msg;
+                        in_handshake = 0;
+                        syslog(LOG_INFO, "VSS: kernel module version: %d",
+                               kernel_modver);
+                        continue;
+                }
+
                 if (len != sizeof(struct hv_vss_msg)) {
                         syslog(LOG_ERR, "read failed; error:%d %s",
                                errno, strerror(errno));