Allow querying a single target in config get API (#15587)

cmd/admin-handlers-config-kv.go

@@ -177,6 +177,11 @@ func (a adminAPIHandlers) SetConfigKVHandler(w http.ResponseWriter, r *http.Requ
 }
 
 // GetConfigKVHandler - GET /minio/admin/v3/get-config-kv?key={key}
+//
+// `key` can be one of three forms:
+// 1. `subsys:target` -> request for config of a single subsystem and target pair.
+// 2. `subsys:` -> request for config of a single subsystem and the default target.
+// 3. `subsys` -> request for config of all targets for the given subsystem.
 func (a adminAPIHandlers) GetConfigKVHandler(w http.ResponseWriter, r *http.Request) {
 	ctx := newContext(r, w, "GetConfigKV")
 
@@ -189,8 +194,22 @@ func (a adminAPIHandlers) GetConfigKVHandler(w http.ResponseWriter, r *http.Requ
 
 	cfg := globalServerConfig.Clone()
 	vars := mux.Vars(r)
-	subSys := vars["key"]
-	subSysConfigs, err := cfg.GetSubsysInfo(subSys)
+	key := vars["key"]
+
+	var subSys, target string
+	{
+		ws := strings.SplitN(key, madmin.SubSystemSeparator, 2)
+		subSys = ws[0]
+		if len(ws) == 2 {
+			if ws[1] == "" {
+				target = madmin.Default
+			} else {
+				target = ws[1]
+			}
+		}
+	}
+
+	subSysConfigs, err := cfg.GetSubsysInfo(subSys, target)
 	if err != nil {
 		writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
 		return
@@ -433,7 +452,7 @@ func (a adminAPIHandlers) GetConfigHandler(w http.ResponseWriter, r *http.Reques
 	}
 	for _, hkv := range hkvs {
 		// We ignore the error below, as we cannot get one.
-		cfgSubsysItems, _ := cfg.GetSubsysInfo(hkv.Key)
+		cfgSubsysItems, _ := cfg.GetSubsysInfo(hkv.Key, "")
 
 		for _, item := range cfgSubsysItems {
 			off := item.Config.Get(config.Enable) == config.EnableOff

go.mod

@@ -48,7 +48,7 @@ require (
 	github.com/minio/dperf v0.4.2
 	github.com/minio/highwayhash v1.0.2
 	github.com/minio/kes v0.20.0
-	github.com/minio/madmin-go v1.4.24
+	github.com/minio/madmin-go v1.4.25
 	github.com/minio/minio-go/v7 v7.0.34
 	github.com/minio/pkg v1.3.0
 	github.com/minio/selfupdate v0.5.0

go.sum

@@ -623,8 +623,8 @@ github.com/minio/highwayhash v1.0.2/go.mod h1:BQskDq+xkJ12lmlUUi7U0M5Swg3EWR+dLT
 github.com/minio/kes v0.20.0 h1:1tyC51Rr8zTregTESuT/QN/iebNMX7B9t7d3xLNMEpE=
 github.com/minio/kes v0.20.0/go.mod h1:3FW1BQkMGQW78yhy+69tUq5bdcf5rnXJizyeKB9a/tc=
 github.com/minio/madmin-go v1.3.5/go.mod h1:vGKGboQgGIWx4DuDUaXixjlIEZOCIp6ivJkQoiVaACc=
-github.com/minio/madmin-go v1.4.24 h1:AFn8/N/E64RUXV4ztGwQcmsKb2uTlwSwiGyk6B37PWY=
-github.com/minio/madmin-go v1.4.24/go.mod h1:ez87VmMtsxP7DRxjKJKD4RDNW+nhO2QF9KSzwxBDQ98=
+github.com/minio/madmin-go v1.4.25 h1:IEJpsTXlHz18/yRI5HxY84KaJdDjUUYdMiC5f8fId4g=
+github.com/minio/madmin-go v1.4.25/go.mod h1:ez87VmMtsxP7DRxjKJKD4RDNW+nhO2QF9KSzwxBDQ98=
 github.com/minio/mc v0.0.0-20220818165341-8c239d16aa37 h1:UE9kHgdza2HB4DDx0nIn0jHRl6YASUomVoKjciMfqjM=
 github.com/minio/mc v0.0.0-20220818165341-8c239d16aa37/go.mod h1:O3pvs5/n57bZ0mpcG/skBuD4pHX6m+wVbW7lw8LO5go=
 github.com/minio/md5-simd v1.1.0/go.mod h1:XpBqgZULrMYD3R+M28PcmP0CkI7PEMzB3U77ZrKZ0Gw=

internal/config/config.go

@@ -1221,8 +1221,10 @@ type SubsysInfo struct {
 	EnvMap map[string]EnvPair
 }
 
-// GetSubsysInfo returns `SubsysInfo`s for all targets for the subsystem.
-func (c Config) GetSubsysInfo(subSys string) ([]SubsysInfo, error) {
+// GetSubsysInfo returns `SubsysInfo`s for all targets for the subsystem, when
+// target is empty. Otherwise returns `SubsysInfo` for the desired target only.
+// To request the default target only, target must be set to `Default`.
+func (c Config) GetSubsysInfo(subSys, target string) ([]SubsysInfo, error) {
 	// Check if config param requested is valid.
 	defKVS1, ok := DefaultKVS[subSys]
 	if !ok {
@@ -1234,6 +1236,20 @@ func (c Config) GetSubsysInfo(subSys string) ([]SubsysInfo, error) {
 		return nil, err
 	}
 
+	if target != "" {
+		found := false
+		for _, t := range targets {
+			if t == target {
+				found = true
+				break
+			}
+		}
+		if !found {
+			return nil, Errorf("there is no target `%s` for subsystem `%s`", target, subSys)
+		}
+		targets = []string{target}
+	}
+
 	// The `Comment` configuration variable is optional but is available to be
 	// set for all sub-systems. It is not present in the `DefaultKVS` map's
 	// values. To enable fetching a configured comment value from the