The hv_utils driver currently supports a "shutdown" operation initiated
from the Hyper-V host. Newer versions of Hyper-V also support a "restart"
operation. So add support for the updated protocol version that has
"restart" support, and perform a clean reboot when such a message is
received from Hyper-V.

To test the restart functionality, run this PowerShell command on the
Hyper-V host:

Restart-VM  <vmname>  -Type Reboot

Signed-off-by: Dexuan Cui <decui@microsoft.com>

---
Changes in v2:
   It's the same as v1.

Changes in v3 (I addressed Michael's comments):
    Used a better version of changelog from  Michael.
    Added a comment about the meaning of shutdown_msg->flags.
    Call schedule_work() at the end of the function for consistency.

 drivers/hv/hv_util.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
index 766bd8457346..d815bea0fda3 100644
--- a/drivers/hv/hv_util.c
+++ b/drivers/hv/hv_util.c

@@ -24,6 +24,8 @@

 #define SD_MAJOR	3
 #define SD_MINOR	0
+#define SD_MINOR_1	1
+#define SD_VERSION_3_1	(SD_MAJOR << 16 | SD_MINOR_1)
 #define SD_VERSION	(SD_MAJOR << 16 | SD_MINOR)

 #define SD_MAJOR_1	1

@@ -50,8 +52,9 @@ static int sd_srv_version;
 static int ts_srv_version;
 static int hb_srv_version;

-#define SD_VER_COUNT 2
+#define SD_VER_COUNT 3
 static const int sd_versions[] = {
+	SD_VERSION_3_1,
 	SD_VERSION,
 	SD_VERSION_1
 };

@@ -118,17 +121,28 @@ static void perform_shutdown(struct work_struct *dummy)
 	orderly_poweroff(true);
 }

+static void perform_restart(struct work_struct *dummy)
+{
+	orderly_reboot();
+}
+
 /*
  * Perform the shutdown operation in a thread context.
  */
 static DECLARE_WORK(shutdown_work, perform_shutdown);

+/*
+ * Perform the restart operation in a thread context.
+ */
+static DECLARE_WORK(restart_work, perform_restart);
+
 static void shutdown_onchannelcallback(void *context)
 {
 	struct vmbus_channel *channel = context;
 	u32 recvlen;
 	u64 requestid;
 	bool execute_shutdown = false;
+	bool execute_reboot = false;
 	u8  *shut_txf_buf = util_shutdown.recv_buffer;

 	struct shutdown_msg_data *shutdown_msg;

@@ -157,6 +171,12 @@ static void shutdown_onchannelcallback(void *context)
 					sizeof(struct vmbuspipe_hdr) +
 					sizeof(struct icmsg_hdr)];

+			/*
+			 * shutdown_msg->flags can be 0 (shut down), 2(reboot),
+			 * or 4(hibernate). It may bitwise-OR 1, which means
+			 * performing the request by force. Linux always tries
+			 * to perform the request by force.
+			 */
 			switch (shutdown_msg->flags) {
 			case 0:
 			case 1:

@@ -166,6 +186,14 @@ static void shutdown_onchannelcallback(void *context)
 				pr_info("Shutdown request received -"
 					    " graceful shutdown initiated\n");
 				break;
+			case 2:
+			case 3:
+				icmsghdrp->status = HV_S_OK;
+				execute_reboot = true;
+
+				pr_info("Restart request received -"
+					    " graceful restart initiated\n");
+				break;
 			default:
 				icmsghdrp->status = HV_E_FAIL;
 				execute_shutdown = false;

@@ -186,6 +214,8 @@ static void shutdown_onchannelcallback(void *context)

 	if (execute_shutdown == true)
 		schedule_work(&shutdown_work);
+	if (execute_reboot == true)
+		schedule_work(&restart_work);