Reduce the number of bootenv vars

clitools/pkg/node/uboot/ab.go

@@ -19,12 +19,39 @@ func ConfigureABBoot(ctx context.Context, nctx *node.NodeContext) error {
 
 	// TODO: configurable from cluster.env
 	return writer.EnsureBootEnv(ctx, BootEnvConfig{
-		BootSource:      "usb",
-		BootPart:        "A",
-		BootDisk:        0,
-		RootfsAPartNum:  2,
-		RootfsBPartNum:  3,
-		DataPartNum:     4,
-		LinuxRootPrefix: "/dev/sda",
+		BootSource: "usb",
+		BootPart:   "A",
+	})
+}
+
+// This is called by the agent controller/osupgrade/handler.go
+func ConfigureNextBoot(ctx context.Context, fwEnvCfgPath string) error {
+
+	exePath, err := os.Executable()
+	if err != nil {
+		return fmt.Errorf("get current executable path: %w", err)
+	}
+
+	writer := NewFWEnvWriter(fwEnvCfgPath, exePath)
+
+	currBootPart, err := writer.GetEnv(ctx, "boot_part")
+	if err != nil {
+		return fmt.Errorf("get boot_part: %w", err)
+	}
+
+	next := "A"
+	if currBootPart == "A" {
+		next = "B"
+
+	}
+
+	currBootSource, err := writer.GetEnv(ctx, "boot_source")
+	if err != nil {
+		return fmt.Errorf("get boot_source: %w", err)
+	}
+
+	return writer.EnsureBootEnv(ctx, BootEnvConfig{
+		BootSource: currBootSource,
+		BootPart:   next,
 	})
 }