Detect seek penalties on Linux/ChromeOS.

chrome/browser/metrics/drive_metrics_provider_linux.cc

+// Copyright 2015 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.
+
+#include "chrome/browser/metrics/drive_metrics_provider.h"
+
+#include <linux/kdev_t.h>  // For MAJOR()/MINOR().
+#include <sys/stat.h>
+#include <string>
+
+#include "base/files/file.h"
+#include "base/files/file_path.h"
+#include "base/files/file_util.h"
+#include "base/strings/stringprintf.h"
+
+#if defined(OS_CHROMEOS)
+#include "base/sys_info.h"
+#endif
+
+namespace {
+
+// See http://www.kernel.org/doc/Documentation/devices.txt for more info.
+const int kScsiMajorNumber = 8;
+const char kRotationalFormat[] = "/sys/block/sd%c/queue/rotational";

[Lei Zhang, 2015/04/03 05:12:08]

I believe after sdz comes sdaa.

[Dan Beam, 2015/04/03 18:25:06]

Done.

+
+}  // namespace
+
+#if !defined(OS_ANDROID)

[Lei Zhang, 2015/04/03 05:12:07]

just exclude the file for android entirely?

[Dan Beam, 2015/04/03 18:25:06]

Done.

+// static
+bool DriveMetricsProvider::HasSeekPenalty(const base::FilePath& path,
+                                          bool* has_seek_penalty) {
+#if defined(OS_CHROMEOS)
+  if (base::SysInfo::GetLsbReleaseBoard() != "parrot") {

[Lei Zhang, 2015/04/03 05:12:07]

What if this returns "unknown" ?

[Dan Beam, 2015/04/03 18:25:05]

Done.

+    // All ChromeOS devices that have ever shipped have SSDs. Except parrots.

[Lei Zhang, 2015/04/03 05:12:08]

some parrots...

[Dan Beam, 2015/04/03 18:25:06]

Done.

+    *has_seek_penalty = false;
+    return true;
+  }
+#endif
+
+  base::File file(path, base::File::FLAG_OPEN);
+  if (!file.IsValid())
+    return false;
+
+  struct stat path_stat;
+  int error = fstat(file.GetPlatformFile(), &path_stat);
+  if (error < 0 || MAJOR(path_stat.st_dev) != kScsiMajorNumber) {
+    // TODO(dbeam): support non-SCSI drives (e.g., LVM)?
+    return false;
+  }
+
+  char sdX = 'a' + MINOR(path_stat.st_dev) / 16;
+  base::FilePath rotational_file(base::StringPrintf(kRotationalFormat, sdX));
+
+  std::string rotates;
+  if (!base::ReadFileToString(rotational_file, &rotates)) {
+    // Old Linux kernel?

[Lei Zhang, 2015/04/03 05:12:07]

How old? Kernels that are too old won't run Chrome properly.

[Dan Beam, 2015/04/03 18:25:05]

don't know. removed.

+    return false;
+  }
+
+  *has_seek_penalty = rotates == "1";
+  return true;
+}
+#endif  // !defined(OS_ANDROID)