diff --git a/hal/gonk/GonkHal.cpp b/hal/gonk/GonkHal.cpp
index d48e4b41106..a6f02ac9939 100644
--- a/hal/gonk/GonkHal.cpp
+++ b/hal/gonk/GonkHal.cpp
@@ -708,27 +708,6 @@ GetCurrentBatteryInformation(hal::BatteryInformation* aBatteryInfo)
 
 namespace {
 
-/**
- * RAII class to help us remember to close file descriptors.
- */
-
-bool WriteToFile(const char *filename, const char *toWrite)
-{
-  int fd = open(filename, O_WRONLY);
-  ScopedClose autoClose(fd);
-  if (fd < 0) {
-    HAL_LOG("Unable to open file %s.", filename);
-    return false;
-  }
-
-  if (write(fd, toWrite, strlen(toWrite)) < 0) {
-    HAL_LOG("Unable to write to file %s.", filename);
-    return false;
-  }
-
-  return true;
-}
-
 // We can write to screenEnabledFilename to enable/disable the screen, but when
 // we read, we always get "mem"!  So we have to keep track ourselves whether
 // the screen is on or not.
@@ -849,7 +828,7 @@ UpdateCpuSleepState()
 
   sInternalLockCpuMonitor->AssertCurrentThreadOwns();
   bool allowed = sCpuSleepAllowed && !sInternalLockCpuCount;
-  WriteToFile(allowed ? wakeUnlockFilename : wakeLockFilename, "gecko");
+  WriteSysFile(allowed ? wakeUnlockFilename : wakeLockFilename, "gecko");
 }
 
 static void
@@ -1257,7 +1236,7 @@ public:
       mRegexes(nullptr)
   {
     // Enable timestamps in kernel's printk
-    WriteToFile("/sys/module/printk/parameters/time", "Y");
+    WriteSysFile("/sys/module/printk/parameters/time", "Y");
   }
 
   NS_DECL_ISUPPORTS
@@ -1559,16 +1538,16 @@ EnsureCpuCGroupExists(const nsACString &aGroup)
 
   nsAutoCString pathPrefix(kDevCpuCtl + aGroup + kSlash);
   nsAutoCString cpuSharesPath(pathPrefix + NS_LITERAL_CSTRING("cpu.shares"));
-  if (cpuShares && !WriteToFile(cpuSharesPath.get(),
-                                nsPrintfCString("%d", cpuShares).get())) {
+  if (cpuShares && !WriteSysFile(cpuSharesPath.get(),
+                                 nsPrintfCString("%d", cpuShares).get())) {
     HAL_LOG("Could not set the cpu share for group %s", cpuSharesPath.get());
     return false;
   }
 
   nsAutoCString notifyOnMigratePath(pathPrefix
     + NS_LITERAL_CSTRING("cpu.notify_on_migrate"));
-  if (!WriteToFile(notifyOnMigratePath.get(),
-                   nsPrintfCString("%d", cpuNotifyOnMigrate).get())) {
+  if (!WriteSysFile(notifyOnMigratePath.get(),
+                    nsPrintfCString("%d", cpuNotifyOnMigrate).get())) {
     HAL_LOG("Could not set the cpu migration notification flag for group %s",
             notifyOnMigratePath.get());
     return false;
@@ -1616,8 +1595,8 @@ EnsureMemCGroupExists(const nsACString &aGroup)
 
   nsAutoCString pathPrefix(kMemCtl + aGroup + kSlash);
   nsAutoCString memSwappinessPath(pathPrefix + NS_LITERAL_CSTRING("memory.swappiness"));
-  if (!WriteToFile(memSwappinessPath.get(),
-                   nsPrintfCString("%d", memSwappiness).get())) {
+  if (!WriteSysFile(memSwappinessPath.get(),
+                    nsPrintfCString("%d", memSwappiness).get())) {
     HAL_LOG("Could not set the memory.swappiness for group %s", memSwappinessPath.get());
     return false;
   }
@@ -1809,9 +1788,9 @@ EnsureKernelLowMemKillerParamsSet()
   adjParams.Cut(adjParams.Length() - 1, 1);
   minfreeParams.Cut(minfreeParams.Length() - 1, 1);
   if (!adjParams.IsEmpty() && !minfreeParams.IsEmpty()) {
-    WriteToFile("/sys/module/lowmemorykiller/parameters/adj", adjParams.get());
-    WriteToFile("/sys/module/lowmemorykiller/parameters/minfree",
-                minfreeParams.get());
+    WriteSysFile("/sys/module/lowmemorykiller/parameters/adj", adjParams.get());
+    WriteSysFile("/sys/module/lowmemorykiller/parameters/minfree",
+                 minfreeParams.get());
   }
 
   // Set the low-memory-notification threshold.
@@ -1821,7 +1800,7 @@ EnsureKernelLowMemKillerParamsSet()
         &lowMemNotifyThresholdKB))) {
 
     // notify_trigger is in pages.
-    WriteToFile("/sys/module/lowmemorykiller/parameters/notify_trigger",
+    WriteSysFile("/sys/module/lowmemorykiller/parameters/notify_trigger",
       nsPrintfCString("%ld", lowMemNotifyThresholdKB * 1024 / page_size).get());
   }
 
@@ -1856,11 +1835,11 @@ SetProcessPriority(int aPid, ProcessPriority aPriority, uint32_t aLRU)
 
   // We try the newer interface first, and fall back to the older interface
   // on failure.
-  if (!WriteToFile(nsPrintfCString("/proc/%d/oom_score_adj", aPid).get(),
-                   nsPrintfCString("%d", oomScoreAdj).get()))
+  if (!WriteSysFile(nsPrintfCString("/proc/%d/oom_score_adj", aPid).get(),
+                    nsPrintfCString("%d", oomScoreAdj).get()))
   {
-    WriteToFile(nsPrintfCString("/proc/%d/oom_adj", aPid).get(),
-                nsPrintfCString("%d", OomAdjOfOomScoreAdj(oomScoreAdj)).get());
+    WriteSysFile(nsPrintfCString("/proc/%d/oom_adj", aPid).get(),
+                 nsPrintfCString("%d", OomAdjOfOomScoreAdj(oomScoreAdj)).get());
   }
 
   HAL_LOG("Assigning pid %d to cgroup %s", aPid, pc->CGroup().get());
diff --git a/xpcom/glue/FileUtils.cpp b/xpcom/glue/FileUtils.cpp
index ad52446299c..699812461f4 100644
--- a/xpcom/glue/FileUtils.cpp
+++ b/xpcom/glue/FileUtils.cpp
@@ -188,6 +188,35 @@ mozilla::ReadSysFile(
 
 #endif /* ReadSysFile_PRESENT */
 
+#ifdef WriteSysFile_PRESENT
+
+bool
+mozilla::WriteSysFile(
+  const char* aFilename,
+  const char* aBuf)
+{
+  size_t aBufSize = strlen(aBuf);
+  int fd = MOZ_TEMP_FAILURE_RETRY(open(aFilename, O_WRONLY));
+  if (fd < 0) {
+    return false;
+  }
+  ScopedClose autoClose(fd);
+  ssize_t bytesWritten;
+  size_t offset = 0;
+  do {
+    bytesWritten = MOZ_TEMP_FAILURE_RETRY(write(fd, aBuf + offset,
+                                                aBufSize - offset));
+    if (bytesWritten == -1) {
+      return false;
+    }
+    offset += bytesWritten;
+  } while (bytesWritten > 0 && offset < aBufSize);
+  MOZ_ASSERT(offset == aBufSize);
+  return true;
+}
+
+#endif /* WriteSysFile_PRESENT */
+
 void
 mozilla::ReadAheadLib(nsIFile* aFile)
 {
diff --git a/xpcom/glue/FileUtils.h b/xpcom/glue/FileUtils.h
index f6242c9d8d5..aaf912b21b8 100644
--- a/xpcom/glue/FileUtils.h
+++ b/xpcom/glue/FileUtils.h
@@ -171,15 +171,19 @@ void ReadAhead(filedesc_t aFd, const size_t aOffset = 0,
 }))
 #endif
 
-/* Define ReadSysFile() only on GONK to avoid unnecessary lubxul bloat.
-Also define it in debug builds, so that unit tests for it can be written
-and run in non-GONK builds. */
+/* Define ReadSysFile() and WriteSysFile() only on GONK to avoid unnecessary
+ * libxul bloat. Also define it in debug builds, so that unit tests for it can
+ * be written and run in non-GONK builds. */
 #if (defined(MOZ_WIDGET_GONK) || defined(DEBUG)) && defined(XP_UNIX)
 
 #ifndef ReadSysFile_PRESENT
 #define ReadSysFile_PRESENT
 #endif /* ReadSysFile_PRESENT */
 
+#ifndef WriteSysFile_PRESENT
+#define WriteSysFile_PRESENT
+#endif /* WriteSysFile_PRESENT */
+
 /**
  * Read the contents of a file.
  * This function is intended for reading a single-lined text files from
@@ -207,6 +211,8 @@ bool ReadSysFile(const char* aFilename, int* aVal);
  */
 bool ReadSysFile(const char* aFilename, bool* aVal);
 
+bool WriteSysFile(const char* aFilename, const char* aBuf);
+
 #endif /* (MOZ_WIDGET_GONK || DEBUG) && XP_UNIX */
 
 } // namespace mozilla