diff --git a/libcutils/android_reboot.c b/libcutils/android_reboot.c
index 6ae23c1..af7e189 100644
--- a/libcutils/android_reboot.c
+++ b/libcutils/android_reboot.c
@@ -14,43 +14,108 @@
  * limitations under the License.
  */
 
-#include <unistd.h>
-#include <sys/reboot.h>
-#include <sys/syscall.h>
-#include <sys/types.h>
-#include <sys/stat.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <mntent.h>
+#include <stdbool.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
+#include <sys/cdefs.h>
+#include <sys/mount.h>
+#include <sys/reboot.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <unistd.h>
 
 #include <cutils/android_reboot.h>
+#include <cutils/klog.h>
+#include <cutils/list.h>
 
-#define UNUSED __attribute__((unused))
+#define TAG "android_reboot"
+#define READONLY_CHECK_MS 5000
+#define READONLY_CHECK_TIMES 50
 
-/* Check to see if /proc/mounts contains any writeable filesystems
- * backed by a block device.
- * Return true if none found, else return false.
+typedef struct {
+    struct listnode list;
+    struct mntent entry;
+} mntent_list;
+
+static bool has_mount_option(const char* opts, const char* opt_to_find)
+{
+  bool ret = false;
+  char* copy = NULL;
+  char* opt;
+  char* rem;
+
+  while ((opt = strtok_r(copy ? NULL : (copy = strdup(opts)), ",", &rem))) {
+      if (!strcmp(opt, opt_to_find)) {
+          ret = true;
+          break;
+      }
+  }
+
+  free(copy);
+  return ret;
+}
+
+static bool is_block_device(const char* fsname)
+{
+    return !strncmp(fsname, "/dev/block", 10);
+}
+
+/* Find all read+write block devices in /proc/mounts and add them to
+ * |rw_entries|.
  */
-static int remount_ro_done(void)
+static void find_rw(struct listnode* rw_entries)
 {
     FILE* fp;
     struct mntent* mentry;
-    int found_rw_fs = 0;
 
     if ((fp = setmntent("/proc/mounts", "r")) == NULL) {
-        /* If we can't read /proc/mounts, just give up. */
-        return 1;
+        KLOG_WARNING(TAG, "Failed to open /proc/mounts.\n");
+        return;
     }
     while ((mentry = getmntent(fp)) != NULL) {
-        if (!strncmp(mentry->mnt_fsname, "/dev/block", 10) && strstr(mentry->mnt_opts, "rw,")) {
-            found_rw_fs = 1;
-            break;
+        if (is_block_device(mentry->mnt_fsname) &&
+            has_mount_option(mentry->mnt_opts, "rw")) {
+            mntent_list* item = (mntent_list*)calloc(1, sizeof(mntent_list));
+            item->entry = *mentry;
+            item->entry.mnt_fsname = strdup(mentry->mnt_fsname);
+            item->entry.mnt_dir = strdup(mentry->mnt_dir);
+            item->entry.mnt_type = strdup(mentry->mnt_type);
+            item->entry.mnt_opts = strdup(mentry->mnt_opts);
+            list_add_tail(rw_entries, &item->list);
         }
     }
     endmntent(fp);
+}
 
-    return !found_rw_fs;
+static void free_entries(struct listnode* entries)
+{
+    struct listnode* node;
+    struct listnode* n;
+    list_for_each_safe(node, n, entries) {
+        mntent_list* item = node_to_item(node, mntent_list, list);
+        free(item->entry.mnt_fsname);
+        free(item->entry.mnt_dir);
+        free(item->entry.mnt_type);
+        free(item->entry.mnt_opts);
+        free(item);
+    }
+}
+
+static mntent_list* find_item(struct listnode* rw_entries, const char* fsname_to_find)
+{
+    struct listnode* node;
+    list_for_each(node, rw_entries) {
+        mntent_list* item = node_to_item(node, mntent_list, list);
+        if (!strcmp(item->entry.mnt_fsname, fsname_to_find)) {
+            return item;
+        }
+    }
+    return NULL;
 }
 
 /* Remounting filesystems read-only is difficult when there are files
@@ -64,38 +129,92 @@
  * repeatedly until there are no more writable filesystems mounted on
  * block devices.
  */
-static void remount_ro(void)
+static void remount_ro(void (*cb_on_remount)(const struct mntent*))
 {
-    int fd, cnt = 0;
+    int fd, cnt;
+    FILE* fp;
+    struct mntent* mentry;
+    struct listnode* node;
+
+    list_declare(rw_entries);
+    list_declare(ro_entries);
+
+    sync();
+    find_rw(&rw_entries);
 
     /* Trigger the remount of the filesystems as read-only,
      * which also marks them clean.
      */
-    fd = open("/proc/sysrq-trigger", O_WRONLY);
+    fd = TEMP_FAILURE_RETRY(open("/proc/sysrq-trigger", O_WRONLY));
     if (fd < 0) {
-        return;
+        KLOG_WARNING(TAG, "Failed to open sysrq-trigger.\n");
+        /* TODO: Try to remount each rw parition manually in readonly mode.
+         * This may succeed if no process is using the partition.
+         */
+        goto out;
     }
-    write(fd, "u", 1);
+    if (TEMP_FAILURE_RETRY(write(fd, "u", 1)) != 1) {
+        close(fd);
+        KLOG_WARNING(TAG, "Failed to write to sysrq-trigger.\n");
+        /* TODO: The same. Manually remount the paritions. */
+        goto out;
+    }
     close(fd);
 
-
     /* Now poll /proc/mounts till it's done */
-    while (!remount_ro_done() && (cnt < 50)) {
-        usleep(100000);
+    cnt = 0;
+    while (cnt < READONLY_CHECK_TIMES) {
+        if ((fp = setmntent("/proc/mounts", "r")) == NULL) {
+            /* If we can't read /proc/mounts, just give up. */
+            KLOG_WARNING(TAG, "Failed to open /proc/mounts.\n");
+            goto out;
+        }
+        while ((mentry = getmntent(fp)) != NULL) {
+            if (!is_block_device(mentry->mnt_fsname) ||
+                !has_mount_option(mentry->mnt_opts, "ro")) {
+                continue;
+            }
+            mntent_list* item = find_item(&rw_entries, mentry->mnt_fsname);
+            if (item) {
+                /* |item| has now been ro remounted. */
+                list_remove(&item->list);
+                list_add_tail(&ro_entries, &item->list);
+            }
+        }
+        endmntent(fp);
+        if (list_empty(&rw_entries)) {
+            /* All rw block devices are now readonly. */
+            break;
+        }
+        TEMP_FAILURE_RETRY(
+            usleep(READONLY_CHECK_MS * 1000 / READONLY_CHECK_TIMES));
         cnt++;
     }
 
-    return;
+    list_for_each(node, &rw_entries) {
+        mntent_list* item = node_to_item(node, mntent_list, list);
+        KLOG_WARNING(TAG, "Failed to remount %s in readonly mode.\n",
+                     item->entry.mnt_fsname);
+    }
+
+    if (cb_on_remount) {
+        list_for_each(node, &ro_entries) {
+            mntent_list* item = node_to_item(node, mntent_list, list);
+            cb_on_remount(&item->entry);
+        }
+    }
+
+out:
+    free_entries(&rw_entries);
+    free_entries(&ro_entries);
 }
 
-
-int android_reboot(int cmd, int flags UNUSED, const char *arg)
+int android_reboot_with_callback(
+    int cmd, int flags __unused, const char *arg,
+    void (*cb_on_remount)(const struct mntent*))
 {
     int ret;
-
-    sync();
-    remount_ro();
-
+    remount_ro(cb_on_remount);
     switch (cmd) {
         case ANDROID_RB_RESTART:
             ret = reboot(RB_AUTOBOOT);
@@ -117,3 +236,7 @@
     return ret;
 }
 
+int android_reboot(int cmd, int flags, const char *arg)
+{
+    return android_reboot_with_callback(cmd, flags, arg, NULL);
+}