validate storage class across pools when setting config (#11320)

```
mc admin config set alias/ storage_class standard=EC:3
```

should only succeed if parity ratio is valid for all
server pools, if not we should fail proactively.

This PR also needs to bring other changes now that
we need to cater for variadic drive counts per pool.

Bonus fixes also various bugs reproduced with

- GetObjectWithPartNumber()
- CopyObjectPartWithOffsets()
- CopyObjectWithMetadata()
- PutObjectPart,PutObject with truncated streams

cmd/config-current.go

@@ -228,7 +228,7 @@ var (
 	globalServerConfigMu sync.RWMutex
 )
 
-func validateConfig(s config.Config, setDriveCount int) error {
+func validateConfig(s config.Config, setDriveCounts []int) error {
 	// We must have a global lock for this so nobody else modifies env while we do.
 	defer env.LockSetEnv()()
 
@@ -251,8 +251,10 @@ func validateConfig(s config.Config, setDriveCount int) error {
 	}
 
 	if globalIsErasure {
-		if _, err := storageclass.LookupConfig(s[config.StorageClassSubSys][config.Default], setDriveCount); err != nil {
-			return err
+		for _, setDriveCount := range setDriveCounts {
+			if _, err := storageclass.LookupConfig(s[config.StorageClassSubSys][config.Default], setDriveCount); err != nil {
+				return err
+			}
 		}
 	}
 
@@ -342,7 +344,7 @@ func validateConfig(s config.Config, setDriveCount int) error {
 	return notify.TestNotificationTargets(GlobalContext, s, NewGatewayHTTPTransport(), globalNotificationSys.ConfiguredTargetIDs())
 }
 
-func lookupConfigs(s config.Config, minSetDriveCount int) {
+func lookupConfigs(s config.Config, setDriveCounts []int) {
 	ctx := GlobalContext
 
 	var err error
@@ -429,7 +431,7 @@ func lookupConfigs(s config.Config, minSetDriveCount int) {
 		logger.LogIf(ctx, fmt.Errorf("Invalid api configuration: %w", err))
 	}
 
-	globalAPIConfig.init(apiConfig, minSetDriveCount)
+	globalAPIConfig.init(apiConfig, setDriveCounts)
 
 	// Initialize remote instance transport once.
 	getRemoteInstanceTransportOnce.Do(func() {
@@ -437,9 +439,17 @@ func lookupConfigs(s config.Config, minSetDriveCount int) {
 	})
 
 	if globalIsErasure {
-		globalStorageClass, err = storageclass.LookupConfig(s[config.StorageClassSubSys][config.Default], minSetDriveCount)
-		if err != nil {
-			logger.LogIf(ctx, fmt.Errorf("Unable to initialize storage class config: %w", err))
+		for i, setDriveCount := range setDriveCounts {
+			sc, err := storageclass.LookupConfig(s[config.StorageClassSubSys][config.Default], setDriveCount)
+			if err != nil {
+				logger.LogIf(ctx, fmt.Errorf("Unable to initialize storage class config: %w", err))
+				break
+			}
+			// if we validated all setDriveCounts and it was successful
+			// proceed to store the correct storage class globally.
+			if i == len(setDriveCounts)-1 {
+				globalStorageClass = sc
+			}
 		}
 	}
 
@@ -553,12 +563,16 @@ func lookupConfigs(s config.Config, minSetDriveCount int) {
 	}
 
 	// Apply dynamic config values
-	logger.LogIf(ctx, applyDynamicConfig(ctx, s))
+	logger.LogIf(ctx, applyDynamicConfig(ctx, newObjectLayerFn(), s))
 }
 
 // applyDynamicConfig will apply dynamic config values.
 // Dynamic systems should be in config.SubSystemsDynamic as well.
-func applyDynamicConfig(ctx context.Context, s config.Config) error {
+func applyDynamicConfig(ctx context.Context, objAPI ObjectLayer, s config.Config) error {
+	if objAPI == nil {
+		return nil
+	}
+
 	// Read all dynamic configs.
 	// API
 	apiConfig, err := api.LookupConfig(s[config.APISubSys][config.Default])
@@ -571,17 +585,16 @@ func applyDynamicConfig(ctx context.Context, s config.Config) error {
 	if err != nil {
 		return fmt.Errorf("Unable to setup Compression: %w", err)
 	}
-	objAPI := newObjectLayerFn()
-	if objAPI != nil {
-		if cmpCfg.Enabled && !objAPI.IsCompressionSupported() {
-			return fmt.Errorf("Backend does not support compression")
-		}
+
+	// Validate if the object layer supports compression.
+	if cmpCfg.Enabled && !objAPI.IsCompressionSupported() {
+		return fmt.Errorf("Backend does not support compression")
 	}
 
 	// Heal
 	healCfg, err := heal.LookupConfig(s[config.HealSubSys][config.Default])
 	if err != nil {
-		logger.LogIf(ctx, fmt.Errorf("Unable to apply heal config: %w", err))
+		return fmt.Errorf("Unable to apply heal config: %w", err)
 	}
 
 	// Crawler
@@ -592,7 +605,7 @@ func applyDynamicConfig(ctx context.Context, s config.Config) error {
 
 	// Apply configurations.
 	// We should not fail after this.
-	globalAPIConfig.init(apiConfig, globalAPIConfig.setDriveCount)
+	globalAPIConfig.init(apiConfig, objAPI.SetDriveCounts())
 
 	globalCompressConfigMu.Lock()
 	globalCompressConfig = cmpCfg
@@ -723,7 +736,7 @@ func loadConfig(objAPI ObjectLayer) error {
 	}
 
 	// Override any values from ENVs.
-	lookupConfigs(srvCfg, objAPI.SetDriveCount())
+	lookupConfigs(srvCfg, objAPI.SetDriveCounts())
 
 	// hold the mutex lock before a new config is assigned.
 	globalServerConfigMu.Lock()