From b0b99866781302ba8b16de033ff2681f20483c14 Mon Sep 17 00:00:00 2001
From: Louis Williams <louis.williams@mongodb.com>
Date: Fri, 22 Sep 2017 13:55:59 -0400
Subject: SERVER-31209 Persist targetVersion in FCV document to indicate an
 upgrade/downgrade in progress.

---
 .../db/commands/feature_compatibility_version.h    | 60 +++++++++++++++++++++-
 1 file changed, 59 insertions(+), 1 deletion(-)

(limited to 'src/mongo/db/commands/feature_compatibility_version.h')

diff --git a/src/mongo/db/commands/feature_compatibility_version.h b/src/mongo/db/commands/feature_compatibility_version.h
index d89b2e996d5..abb48b82101 100644
--- a/src/mongo/db/commands/feature_compatibility_version.h
+++ b/src/mongo/db/commands/feature_compatibility_version.h
@@ -40,6 +40,18 @@ namespace mongo {
 class BSONObj;
 class OperationContext;
 
+/**
+ * Store state of featureCompatibilityVersion document.
+ **/
+struct FeatureCompatibilityVersionInfo {
+    ServerGlobalParams::FeatureCompatibility::Version version;
+    ServerGlobalParams::FeatureCompatibility::Version targetVersion;
+
+    FeatureCompatibilityVersionInfo()
+        : version(ServerGlobalParams::FeatureCompatibility::Version::kUnset),
+          targetVersion(ServerGlobalParams::FeatureCompatibility::Version::kUnset) {}
+};
+
 /**
  * Startup parameter to ignore featureCompatibilityVersion checks. This parameter cannot be set if
  * the node is started with --replSet, --master, or --slave. This should never be set by end users.
@@ -53,12 +65,13 @@ public:
     static constexpr StringData kDatabase = "admin"_sd;
     static constexpr StringData kParameterName = "featureCompatibilityVersion"_sd;
     static constexpr StringData kVersionField = "version"_sd;
+    static constexpr StringData kTargetVersionField = "targetVersion"_sd;
 
     /**
      * Parses the featureCompatibilityVersion document from admin.system.version, and returns the
      * version.
      */
-    static StatusWith<ServerGlobalParams::FeatureCompatibility::Version> parse(
+    static StatusWith<FeatureCompatibilityVersionInfo> parse(
         const BSONObj& featureCompatibilityVersionDoc);
 
     static StringData toString(ServerGlobalParams::FeatureCompatibility::Version version) {
@@ -67,6 +80,8 @@ public:
                 return FeatureCompatibilityVersionCommandParser::kVersion36;
             case ServerGlobalParams::FeatureCompatibility::Version::k34:
                 return FeatureCompatibilityVersionCommandParser::kVersion34;
+            case ServerGlobalParams::FeatureCompatibility::Version::kUnset:
+                return FeatureCompatibilityVersionCommandParser::kVersionUnset;
             default:
                 MONGO_UNREACHABLE;
         }
@@ -79,6 +94,27 @@ public:
      */
     static void set(OperationContext* opCtx, StringData version);
 
+    /**
+     * Indicate intent to perform an upgrade. Should be set before schemas are modified.
+     * This sets the 'targetVersion' field only.
+     * Use unsetTargetUpgradeOrDowngrade to indicate that the schemas have completed the upgrading.
+     */
+    static void setTargetUpgrade(OperationContext* opCtx, StringData version);
+
+    /**
+     * Indicate intent to perform a downgrade. Should be set before schemas are modified.
+     * This atomically updates both the 'version' and 'targetVersion' fields.
+     * Use unsetTargetUpgradeOrDowngrade to indicate that the schemas have completed downgrading.
+     */
+    static void setTargetDowngrade(OperationContext* opCtx, StringData version);
+
+    /**
+     * Indicate the completion of an upgrade or downgrade. Should be set only when schemas are
+     * done being upgraded or modified.
+     * Unsets the 'targetVersion' field and updates the 'version' field.
+     */
+    static void unsetTargetUpgradeOrDowngrade(OperationContext* opCtx, StringData version);
+
     /**
      * If there are no non-local databases and we are not running with --shardsvr, set
      * featureCompatibilityVersion to the latest value.
@@ -104,6 +140,28 @@ public:
      * Resets the server parameter to its default value on commit.
      */
     static void onDropCollection(OperationContext* opCtx);
+
+private:
+    /**
+     * Validate version. Uasserts if invalid.
+     */
+    static void _validateVersion(StringData version);
+
+    /**
+     * Close incoming connections from interal clients who cannot speak our highest wire protocol
+     * version.
+     */
+    static void _closeConnectionsBelowVersion(OperationContext* opCtx,
+                                              FeatureCompatibilityVersionInfo versionInfo);
+
+    /**
+     * Build update command.
+     */
+    typedef stdx::function<void(BSONObjBuilder)> UpdateBuilder;
+    static void _runUpdateCommand(OperationContext* opCtx,
+                                  StringData version,
+                                  UpdateBuilder callback);
 };
 
+
 }  // namespace mongo
-- 
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