Implement device watchdog.

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

-// +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)
+        })
 }