From 5f85d1fb0a2f7dd85b2f1acabcce2d227a60b29c Mon Sep 17 00:00:00 2001
From: Tao Bao <tbao@google.com>
Date: Tue, 28 Mar 2017 21:12:36 -0700
Subject: Log the error message when failing to mount/umount.

Test: Observe the error messaage for a umount failure case.
Bug: 36686818
Change-Id: I28e335c2df4454dd0192f95e3909599fcc9dc1c0
---
 Android.mk |  6 ++++--
 mounts.cpp | 26 ++++++++++++++++++--------
 2 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/Android.mk b/Android.mk
index 58b8a2240..037aa1673 100644
--- a/Android.mk
+++ b/Android.mk
@@ -29,9 +29,11 @@ include $(BUILD_STATIC_LIBRARY)
 # ===============================
 include $(CLEAR_VARS)
 LOCAL_SRC_FILES := mounts.cpp
-LOCAL_CLANG := true
-LOCAL_CFLAGS := -Wall -Wno-unused-parameter -Werror
+LOCAL_CFLAGS := \
+    -Wall \
+    -Werror
 LOCAL_MODULE := libmounts
+LOCAL_STATIC_LIBRARIES := libbase
 include $(BUILD_STATIC_LIBRARY)
 
 # recovery (static executable)
diff --git a/mounts.cpp b/mounts.cpp
index f23376b06..fbcbac014 100644
--- a/mounts.cpp
+++ b/mounts.cpp
@@ -27,6 +27,8 @@
 #include <string>
 #include <vector>
 
+#include <android-base/logging.h>
+
 struct MountedVolume {
     std::string device;
     std::string mount_point;
@@ -75,15 +77,23 @@ MountedVolume* find_mounted_volume_by_mount_point(const char* mount_point) {
 }
 
 int unmount_mounted_volume(MountedVolume* volume) {
-    // Intentionally pass the empty string to umount if the caller tries
-    // to unmount a volume they already unmounted using this
-    // function.
-    std::string mount_point = volume->mount_point;
-    volume->mount_point.clear();
-    return umount(mount_point.c_str());
+  // Intentionally pass the empty string to umount if the caller tries to unmount a volume they
+  // already unmounted using this function.
+  std::string mount_point = volume->mount_point;
+  volume->mount_point.clear();
+  int result = umount(mount_point.c_str());
+  if (result == -1) {
+    PLOG(WARNING) << "Failed to umount " << mount_point;
+  }
+  return result;
 }
 
 int remount_read_only(MountedVolume* volume) {
-    return mount(volume->device.c_str(), volume->mount_point.c_str(), volume->filesystem.c_str(),
-                 MS_NOATIME | MS_NODEV | MS_NODIRATIME | MS_RDONLY | MS_REMOUNT, 0);
+  int result = mount(volume->device.c_str(), volume->mount_point.c_str(),
+                     volume->filesystem.c_str(),
+                     MS_NOATIME | MS_NODEV | MS_NODIRATIME | MS_RDONLY | MS_REMOUNT, 0);
+  if (result == -1) {
+    PLOG(WARNING) << "Failed to remount read-only " << volume->mount_point;
+  }
+  return result;
 }
-- 
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