[PATCH 1/2] Drivers: hv: vmbus: Introduce table of VMBus protocol versions

[Andrea Parri <parri.andrea@gmail.com>]

The technique used to get the next VMBus version seems increasisly
clumsy as the number of VMBus versions increases.  Performance is
not a concern since this is only done once during system boot; it's
just that we'll end up with more lines of code than is really needed.

As an alternative, introduce a table with the version numbers listed
in order (from the most recent to the oldest).  vmbus_connect() loops
through the versions listed in the table until it gets an accepted
connection or gets to the end of the table (invalid version).

Suggested-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
---
 drivers/hv/connection.c | 51 +++++++++++++++--------------------------
 include/linux/hyperv.h  |  2 --
 2 files changed, 19 insertions(+), 34 deletions(-)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 6e4c015783ffc..90a32c9d79403 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -40,29 +40,19 @@ EXPORT_SYMBOL_GPL(vmbus_connection);
 __u32 vmbus_proto_version;
 EXPORT_SYMBOL_GPL(vmbus_proto_version);
 
-static __u32 vmbus_get_next_version(__u32 current_version)
-{
-	switch (current_version) {
-	case (VERSION_WIN7):
-		return VERSION_WS2008;
-
-	case (VERSION_WIN8):
-		return VERSION_WIN7;
-
-	case (VERSION_WIN8_1):
-		return VERSION_WIN8;
-
-	case (VERSION_WIN10):
-		return VERSION_WIN8_1;
-
-	case (VERSION_WIN10_V5):
-		return VERSION_WIN10;
-
-	case (VERSION_WS2008):
-	default:
-		return VERSION_INVAL;
-	}
-}
+/*
+ * Table of VMBus versions listed from newest to oldest; the table
+ * must terminate with VERSION_INVAL.
+ */
+__u32 vmbus_versions[] = {
+	VERSION_WIN10_V5,
+	VERSION_WIN10,
+	VERSION_WIN8_1,
+	VERSION_WIN8,
+	VERSION_WIN7,
+	VERSION_WS2008,
+	VERSION_INVAL
+};
 
 int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo, u32 version)
 {
@@ -169,8 +159,8 @@ int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo, u32 version)
  */
 int vmbus_connect(void)
 {
-	int ret = 0;
 	struct vmbus_channel_msginfo *msginfo = NULL;
+	int i, ret = 0;
 	__u32 version;
 
 	/* Initialize the vmbus connection */
@@ -244,21 +234,18 @@ int vmbus_connect(void)
 	 * version.
 	 */
 
-	version = VERSION_CURRENT;
+	for (i = 0; ; i++) {
+		version = vmbus_versions[i];
+		if (version == VERSION_INVAL)
+			goto cleanup;
 
-	do {
 		ret = vmbus_negotiate_version(msginfo, version);
 		if (ret == -ETIMEDOUT)
 			goto cleanup;
 
 		if (vmbus_connection.conn_state == CONNECTED)
 			break;
-
-		version = vmbus_get_next_version(version);
-	} while (version != VERSION_INVAL);
-
-	if (version == VERSION_INVAL)
-		goto cleanup;
+	}
 
 	vmbus_proto_version = version;
 	pr_info("Vmbus version:%d.%d\n",
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index b4a017093b697..7073f1eb3618c 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -194,8 +194,6 @@ static inline u32 hv_get_avail_to_write_percent(
 
 #define VERSION_INVAL -1
 
-#define VERSION_CURRENT VERSION_WIN10_V5
-
 /* Make maximum size of pipe payload of 16K */
 #define MAX_PIPE_DATA_PAYLOAD		(sizeof(u8) * 16384)
 
-- 
2.23.0