tsmon: read hostname and region from config file

common/tsmon/target/flags.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package target
 
 import (
         "flag"
         "os"
         "regexp"
@@ skipping 48 matching lines @@
 // SetDefaultsFromHostname computes the expensive default values for hostname,
 // region and network fields.
 func (fl *Flags) SetDefaultsFromHostname() {
         if fl.SysInfo == nil {
                 hostname, region := getFQDN()
                 fl.SysInfo = &SysInfo{Hostname: hostname, Region: region}
         }
         network := getNetwork(fl.SysInfo.Hostname)
         hostname := fl.SysInfo.Hostname
 
-        if fl.AutoGenHostname {
-                hostname = "autogen:" + hostname
-        }
         if fl.DeviceHostname == "" {
                 fl.DeviceHostname = hostname
         }
         if fl.DeviceRegion == "" {
                 fl.DeviceRegion = fl.SysInfo.Region
         }
         if fl.DeviceNetwork == "" {
                 fl.DeviceNetwork = network
         }
         if fl.TaskRegion == "" {
                 fl.TaskRegion = fl.SysInfo.Region
         }
         if fl.TaskHostname == "" {
                 fl.TaskHostname = hostname
         }
+        if fl.AutoGenHostname {
+                fl.DeviceHostname = "autogen:" + fl.DeviceHostname
+                fl.TaskHostname = "autogen:" + fl.TaskHostname
+        }
 }
 
 // Register adds tsmon target related flags to a FlagSet.
 func (fl *Flags) Register(f *flag.FlagSet) {
         f.Var(&fl.TargetType, "ts-mon-target-type",
                 "the type of target that is being monitored ("+targetTypeEnum.Choices()+")")
         f.StringVar(&fl.DeviceHostname, "ts-mon-device-hostname", fl.DeviceHostname,
                 "name of this device")
         f.StringVar(&fl.DeviceRegion, "ts-mon-device-region", fl.DeviceRegion,
                 "name of the region this devices lives in")
@@ skipping 27 matching lines @@
         }
         return "unknown", "unknown"
 }
 
 func getNetwork(hostname string) string {
         if m := regexp.MustCompile(`^([\w-]*?-[acm]|master)(\d+)a?$`).FindStringSubmatch(hostname); m != nil {
                 return m[2]
         }
         return ""
 }