Detect seek penalties on Mac.

chrome/browser/metrics/drive_metrics_provider_mac.mm

 // 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 <CoreFoundation/CoreFoundation.h>
+#include <DiskArbitration/DiskArbitration.h>
+#import <Foundation/NSURL.h>

[Dan Beam, 2015/04/08 00:15:54]

full disclosure: i little idea when to #include vs #import

[groby-ooo-7-16, 2015/04/08 00:41:02]

You guessed well :) (If it's ObjC stuff, it's import, otherwise #include. I.e.
square brackets == import ;)

[groby-ooo-7-16, 2015/04/08 00:41:02]

Instead of picking on NSUrl, just use 
  #import <Cocoa/Cocoa.h>

That's the default Chromium pattern.

[Dan Beam, 2015/04/08 01:04:43]

that was actually exactly my reasoning, lol

[Dan Beam, 2015/04/08 01:04:43]

Done.

+#include <IOKit/IOKitLib.h>
+#include <IOKit/storage/IOStorageDeviceCharacteristics.h>
+
+#include "base/mac/foundation_util.h"
+#include "base/mac/mac_util.h"
+#include "base/mac/scoped_cftyperef.h"
+#include "base/mac/scoped_ioobject.h"
+
 // static
 bool DriveMetricsProvider::HasSeekPenalty(const base::FilePath& path,
                                           bool* has_seek_penalty) {
-  // TODO(dbeam): implement.
-  return false;
+  NSURL* url = [NSURL fileURLWithPath:base::mac::FilePathToNSString(path)];
+  if (!url)

[groby-ooo-7-16, 2015/04/08 00:41:02]

Can't return nil

[Dan Beam, 2015/04/08 01:04:43]

Done.

+    return false;
+
+  NSURL* volume;

[groby-ooo-7-16, 2015/04/08 00:41:02]

Cocoa usually spells out the type, so volumeUrl

[Dan Beam, 2015/04/08 01:04:43]

Done.

+  if (![url getResourceValue:&volume forKey:NSURLVolumeURLKey error:nil])
+    return false;
+
+  base::ScopedCFTypeRef<DASessionRef> session(DASessionCreate(nullptr));

[groby-ooo-7-16, 2015/04/08 00:41:02]

Please don't nullptr - kCFAllocatorDefault (It's the same, but more readable)

[Dan Beam, 2015/04/08 01:04:43]

Done.

+  if (!session)
+    return false;
+
+  base::ScopedCFTypeRef<DADiskRef> disk(
+      DADiskCreateFromVolumePath(nullptr, session, (CFURLRef)volume));

[Dan Beam, 2015/04/08 00:17:35]

i don't know our stance on toll-free bridging... or how we generally do it

[groby-ooo-7-16, 2015/04/08 00:41:02]

nullptr is kCFAllocatorDefault

[groby-ooo-7-16, 2015/04/08 00:41:02]

base::mac::NSToCFCast(volumeUrl)

[Dan Beam, 2015/04/08 01:04:43]

Done.

[Dan Beam, 2015/04/08 01:04:43]

Done.

+  if (!disk)
+    return false;
+
+  base::mac::ScopedIOObject<io_object_t> media(DADiskCopyIOMedia(disk));
+  base::ScopedCFTypeRef<CFDictionaryRef> characteristics(
+      static_cast<CFDictionaryRef>(IORegistryEntrySearchCFProperty(
+          media,
+          kIOServicePlane,
+          CFSTR(kIOPropertyDeviceCharacteristicsKey),
+          kCFAllocatorDefault,

[Dan Beam, 2015/04/08 00:17:35]

also i wasn't sure when to pass kCFAllocatorDefault vs nullptr, so i just did
what the Chromium-specific uses of these functions did

[groby-ooo-7-16, 2015/04/08 00:41:02]

Heh - see above :)

+          kIORegistryIterateRecursively | kIORegistryIterateParents)));
+  if (!characteristics)
+    return false;
+
+  CFStringRef type = base::mac::GetValueFromDictionary<CFStringRef>(
+      characteristics, CFSTR(kIOPropertyMediumTypeKey));
+  if (!type)
+    return false;
+
+  return [@"Solid State" isEqualToString:(NSString*)type];

[groby-ooo-7-16, 2015/04/08 00:41:02]

Eeeeeeew. base::mac::CFToNSCast, please. :)

[Dan Beam, 2015/04/08 01:04:43]

Done.

 }