log/filelogger, logpolicy: put Windows disk logs next to the log config

filelogger always wrote under %ProgramData%\Tailscale\Logs, even though
logpolicy already picks %LocalAppData%\Tailscale for its config when
tailscaled isn't privileged enough for %ProgramData%. A tailscaled run by
a regular user therefore logged "failed to create local log directory" and
kept no disk logs. Take the directory from the caller instead: logpolicy
passes the Logs subdirectory of whichever directory it chose, which is the
same %ProgramData% path as before for the service.

Updates #2791

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: I3b5d7f9a1c3e5b7d9f1a3c5e7b9d1f3a5c7e9b1d

log/filelogger/log.go

@@ -25,17 +25,17 @@ const (
 	maxFiles = 50
 )
 
-// New returns a logf wrapper that appends to local disk log
-// files on Windows, rotating old log files as needed to stay under
-// file count & byte limits.
-func New(fileBasePrefix, logID string, logf logger.Logf) logger.Logf {
+// New returns a logf wrapper that appends to local disk log files in dir on
+// Windows, creating dir if needed and rotating old log files as needed to
+// stay under file count & byte limits. If dir can't be created, it logs
+// that and returns logf unchanged.
+func New(dir, fileBasePrefix, logID string, logf logger.Logf) logger.Logf {
 	if runtime.GOOS != "windows" {
 		panic("not yet supported on any platform except Windows")
 	}
 	if logf == nil {
 		panic("nil logf")
 	}
-	dir := filepath.Join(os.Getenv("ProgramData"), "Tailscale", "Logs")
 
 	if err := os.MkdirAll(dir, 0700); err != nil {
 		log.Printf("failed to create local log directory; not writing logs to disk: %v", err)

logpolicy/logpolicy.go

@@ -687,7 +687,10 @@ func (opts Options) init(disableLogging bool) (*logtail.Config, *Policy) {
 		logID := newc.PublicID.String()
 		exe, _ := os.Executable()
 		if strings.EqualFold(filepath.Base(exe), "tailscaled.exe") {
-			diskLogf := filelogger.New("tailscale-service", logID, lw.Logf)
+			// Alongside the log config: %ProgramData%\Tailscale\Logs for
+			// the service, or %LocalAppData%\Tailscale\Logs for a tailscaled
+			// run by a regular user. See LogsDir.
+			diskLogf := filelogger.New(filepath.Join(opts.Dir, "Logs"), "tailscale-service", logID, lw.Logf)
 			logOutput = logger.FuncWriter(diskLogf)
 		}
 	}