Move stack dump dir to exec root

Dump stack dumps to exec root instead of daemon root.
When no path is provided to the stack dumper, such is the case with
SIGQUIT, dump to stderr.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>
(cherry picked from commit 0bd720b28dc7b416fe2193bdafaca011ec24d032)
Signed-off-by: Victor Vieux <victorvieux@gmail.com>

daemon/daemon.go

@@ -692,7 +692,11 @@ func NewDaemon(config *Config, registryService registry.Service, containerdRemot
 
 	// set up SIGUSR1 handler on Unix-like systems, or a Win32 global event
 	// on Windows to dump Go routine stacks
-	d.setupDumpStackTrap(config.Root)
+	stackDumpDir := config.Root
+	if execRoot := config.GetExecRoot(); execRoot != "" {
+		stackDumpDir = execRoot
+	}
+	d.setupDumpStackTrap(stackDumpDir)
 
 	return d, nil
 }

pkg/signal/trap.go

@@ -83,15 +83,21 @@ func DumpStacks(dir string) (string, error) {
 		bufferLen *= 2
 	}
 	buf = buf[:stackSize]
-	path := filepath.Join(dir, fmt.Sprintf(stacksLogNameTemplate, strings.Replace(time.Now().Format(time.RFC3339), ":", "", -1)))
-	f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY, 0666)
-	if err != nil {
-		return "", errors.Wrap(err, "failed to open file to write the goroutine stacks")
+	var f *os.File
+	if dir != "" {
+		path := filepath.Join(dir, fmt.Sprintf(stacksLogNameTemplate, strings.Replace(time.Now().Format(time.RFC3339), ":", "", -1)))
+		var err error
+		f, err = os.OpenFile(path, os.O_CREATE|os.O_WRONLY, 0666)
+		if err != nil {
+			return "", errors.Wrap(err, "failed to open file to write the goroutine stacks")
+		}
+		defer f.Close()
+		defer f.Sync()
+	} else {
+		f = os.Stderr
 	}
-	defer f.Close()
 	if _, err := f.Write(buf); err != nil {
 		return "", errors.Wrap(err, "failed to write goroutine stacks")
 	}
-	f.Sync()
-	return path, nil
+	return f.Name(), nil
 }