update_engine: use librootdev

utils.cc

 // Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "update_engine/utils.h"
 
 #include <sys/mount.h>
 #include <sys/resource.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 
 #include <algorithm>
 
-#include "base/file_path.h"
-#include "base/file_util.h"
-#include "base/rand_util.h"
-#include "base/string_util.h"
-#include "base/logging.h"
+#include <base/file_path.h>
+#include <base/file_util.h>
+#include <base/rand_util.h>
+#include <base/string_util.h>
+#include <base/logging.h>
+#include <rootdev/rootdev.h>
+
 #include "update_engine/file_writer.h"
 #include "update_engine/omaha_request_params.h"
 #include "update_engine/subprocess.h"
 
 using std::min;
 using std::string;
 using std::vector;
 
 namespace chromeos_update_engine {
 
@@ skipping 320 matching lines @@
     return false;
   return 0 == str.compare(str.size() - suffix.size(), suffix.size(), suffix);
 }
 
 bool StringHasPrefix(const std::string& str, const std::string& prefix) {
   if (prefix.size() > str.size())
     return false;
   return 0 == str.compare(0, prefix.size(), prefix);
 }
 
-const string BootDevice() {
-  string proc_cmdline;
-  if (!ReadFileToString("/proc/cmdline", &proc_cmdline))
-    return "";
-  // look for "root=" in the command line
-  string::size_type pos = 0;
-  if (!StringHasPrefix(proc_cmdline, "root=")) {
-    pos = proc_cmdline.find(" root=") + 1;
-  }
-  if (pos == string::npos) {
-    // can't find root=
+const std::string BootDevice() {
+  char boot_path[PATH_MAX];
+  // Resolve the boot device path fully, including dereferencing
+  // through dm-verity.
+  int ret = rootdev(boot_path, sizeof(boot_path), true, false);
+
+  if (ret < 0) {
+    LOG(ERROR) << "rootdev failed to find the root device";
     return "";
   }
-  // at this point, pos is the point in the string where "root=" starts
-  string ret;
-  pos += strlen("root=");  // advance to the device name itself
-  while (pos < proc_cmdline.size()) {
-    char c = proc_cmdline[pos];
-    if (c == ' ')
-      break;
-    ret += c;
-    pos++;
-  }
-  return ret;
-  // TODO(adlr): use findfs to figure out UUID= or LABEL= filesystems
+  LOG_IF(WARNING, ret > 0) << "rootdev found a device name with no device node";
+
+  // This local variable is used to construct the return string and is not
+  // passed around after use.
+  return boot_path;
 }
 
 const string BootKernelDevice(const std::string& boot_device) {
   // Currntly this assumes the last digit of the boot device is
   // 3, 5, or 7, and changes it to 2, 4, or 6, respectively, to
   // get the kernel device.
   string ret = boot_device;
   if (ret.empty())
     return ret;
   char last_char = ret[ret.size() - 1];
@@ skipping 61 matching lines @@
   int min = value - range / 2;
   int max = value + range - range / 2;
   return base::RandInt(min, max);
 }
 
 const char* const kStatefulPartition = "/mnt/stateful_partition";
 
 }  // namespace utils
 
 }  // namespace chromeos_update_engine