Implement device watchdog.

go/src/infra/tools/device_watchdog/main.go

Index: go/src/infra/tools/device_watchdog/main.go
diff --git a/go/src/infra/tools/device_watchdog/main.go b/go/src/infra/tools/device_watchdog/main.go
index b76425ba08aeba2a95d8b1af1d74efe470bb7270..9822c4fffff60105956a8cee0a4da51486aac170 100644
--- a/go/src/infra/tools/device_watchdog/main.go
+++ b/go/src/infra/tools/device_watchdog/main.go
@@ -1,12 +1,178 @@
-// +build !windows
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
 
+// +build android
+
+// Watchdog daemon for android devices. It will attempt to reboot the device
+// if its uptime exceeds a specified maximum.
 package main
 
+/*
+#cgo LDFLAGS: -landroid -llog
+
+#include <android/log.h>
+#include <string.h>
+*/
+import "C"
+
 import (
-	"C"
+	"flag"
 	"fmt"
+	"io/ioutil"
+	"os"
+	"strconv"
+	"strings"
+	"syscall"
+	"time"
+	"unsafe"
+
+	"github.com/luci/luci-go/common/runtime/paniccatcher"
 )
 
+var (
+	logHeader = C.CString("CIT_DeviceWatchdog")
+)
+
+type logLevel int
+
+const (
+	logInfo = iota
+	logWarning
+	logError
+)
+
+const (
+	stdInFd  = 0
+	stdOutFd = 1
+	stdErrFd = 2
+)
+
+func (l logLevel) getLogLevel() C.int {
+	switch l {
+	case logInfo:
+		return C.ANDROID_LOG_INFO
+	case logWarning:
+		return C.ANDROID_LOG_WARN
+	case logError:
+		return C.ANDROID_LOG_ERROR
+	default:
+		panic("Unknown log level.")
+	}
+}
+
+func logcatLog(level logLevel, format string, args ...interface{}) {
+	cmsg := C.CString(fmt.Sprintf(format, args...))
+	defer C.free(unsafe.Pointer(cmsg))
+	C.__android_log_write(level.getLogLevel(), logHeader, cmsg)
+}
+
+// Spawn a child process via fork, create new process group, chdir and
+// redirect std in and out to /dev/null.
+func daemonize() (int, error) {
+	ret, _, errno := syscall.Syscall(syscall.SYS_FORK, 0, 0, 0)
+	pid := int(ret)
+	if errno != 0 {
+		return 0, errno
+	}
+	if pid > 0 {
+		return pid, nil
+	}
+
+	_, err := syscall.Setsid()
+	if err != nil {
+		return 0, err
+	}
+
+	f, err := os.Open("/dev/null")
+	if err != nil {
+		return 0, err
+	}
+	fd := f.Fd()
+	syscall.Dup2(int(fd), stdInFd)
+	syscall.Dup2(int(fd), stdOutFd)
+	syscall.Dup2(int(fd), stdErrFd)
+
+	return pid, nil
+}
+
+// Read from /proc/uptime. Expected format:
+// "uptime_in_seconds cpu_idle_time_in_seconds"
+func getDeviceUptime() (time.Duration, error) {
+	bytes, err := ioutil.ReadFile("/proc/uptime")
+	if err != nil {
+		return 0, fmt.Errorf("unable to open /proc/uptime: %s", err.Error())
+	}
+	// Split on the space to get uptime and drop cpu idle time.
+	uptimeFields := strings.Fields(string(bytes))
+	if len(uptimeFields) == 0 {
+		return 0, fmt.Errorf("unable to parse /proc/uptime")
+	}
+	uptime, err := strconv.ParseFloat(uptimeFields[0], 64)
+	if err != nil {
+		return 0, fmt.Errorf("unable to parse uptime: %s", err.Error())
+	}
+	return time.Duration(uptime * float64(time.Second)), nil
+}
+
+// Reboot device by writing to sysrq-trigger. See:
+// https://www.kernel.org/doc/Documentation/sysrq.txt
+func rebootDevice() error {
+	fd, err := os.OpenFile("/proc/sysrq-trigger", os.O_WRONLY, 0)
+	if err != nil {
+		return fmt.Errorf("Can't open /proc/sysrq-trigger: %s", err.Error())
+	}
+	defer fd.Close()
+	_, err = fd.Write([]byte("b"))
+	if err != nil {
+		return fmt.Errorf("Can't reboot: %s", err.Error())
+	}
+	return fmt.Errorf("I just rebooted. How am I still alive?!?\n")
+}
+
+func realMain() int {
+	maxUptimeFlag := flag.Int("max-uptime", 120, "Maximum uptime in minutes before a reboot is triggered.")
+	flag.Parse()
+
+	os.Chdir("/")
+	pid, err := daemonize()
+	if err != nil {
+		logcatLog(logError, "Failed to daemonize: %s", err.Error())
+		return 1
+	}
+	if pid > 0 {
+		logcatLog(logInfo, "Child spawned with pid %d, exiting parent\n", pid)
+		return 0
+	}
+
+	maxUptime := time.Duration(*maxUptimeFlag) * time.Minute
+	for {
+		uptime, err := getDeviceUptime()
+		if err != nil {
+			logcatLog(logError, "Failed to get uptime: %s", err.Error())
+			return 1
+		}
+
+		if uptime > maxUptime {
+			logcatLog(logInfo, "Max uptime exceeded: (%.2f > %.2f)\n", float64(uptime)/float64(time.Minute), float64(maxUptime)/float64(time.Minute))

[dnj, 2016/08/17 00:42:36]

nit: render time as "%s" and pass the duration directly. The string rendering of
a time.Duration looks pretty decent.

e.g., https://play.golang.org/p/RfW_QrL3BC

[bpastene, 2016/08/17 02:30:33]

Ahhhh, that's so much better. Done

+			break
+		} else {

[dnj, 2016/08/17 00:42:36]

nit: You don't need this "else" clause, since you break above.

[bpastene, 2016/08/17 02:30:33]

Done.

+			logcatLog(logInfo, "No need to reboot, uptime < max_uptime: (%.2f < %.2f)\n", float64(uptime)/float64(time.Minute), float64(maxUptime)/float64(time.Minute))

[dnj, 2016/08/17 00:42:36]

(same here)

[bpastene, 2016/08/17 02:30:33]

Done.

+		}
+		time.Sleep(maxUptime - uptime + time.Second)
+	}
+	if err = rebootDevice(); err != nil {
+		logcatLog(logError, "Failed to reboot device: %s", err.Error())
+		return 1
+	}
+	return 0
+}
+
 func main() {
-	fmt.Println("Is this thing working?")
+	paniccatcher.Do(func() {
+		os.Exit(realMain())
+	}, func(p *paniccatcher.Panic) {
+		logcatLog(logError, "Panic: %s\n%s", p.Reason, p.Stack)
+		os.Exit(1)
+	})
 }