Media Galleries: Access MTP devices by file ids rather than file paths.

chrome/browser/media_galleries/linux/mtp_device_delegate_impl_linux.cc

Index: chrome/browser/media_galleries/linux/mtp_device_delegate_impl_linux.cc
diff --git a/chrome/browser/media_galleries/linux/mtp_device_delegate_impl_linux.cc b/chrome/browser/media_galleries/linux/mtp_device_delegate_impl_linux.cc
index 86370e7ecd49c4b5896052ec3eaf4af049f6ffd8..f816c9e2cc57821a5b7a590d6ac6b3b8dbeb4baf 100644
--- a/chrome/browser/media_galleries/linux/mtp_device_delegate_impl_linux.cc
+++ b/chrome/browser/media_galleries/linux/mtp_device_delegate_impl_linux.cc
@@ -5,16 +5,19 @@
 #include "chrome/browser/media_galleries/linux/mtp_device_delegate_impl_linux.h"
 
 #include <algorithm>
+#include <set>
+#include <vector>
 
 #include "base/bind.h"
-#include "base/files/file_path.h"
 #include "base/numerics/safe_conversions.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "chrome/browser/media_galleries/linux/mtp_device_task_helper.h"
 #include "chrome/browser/media_galleries/linux/mtp_device_task_helper_map_service.h"
 #include "chrome/browser/media_galleries/linux/snapshot_file_details.h"
-#include "content/public/browser/browser_thread.h"
 #include "net/base/io_buffer.h"
+#include "third_party/cros_system_api/dbus/service_constants.h"
 
 namespace {
 
@@ -80,7 +83,7 @@ void OpenStorageOnUIThread(
   task_helper->OpenStorage(storage_name, reply_callback);
 }
 
-// Enumerates the |root| directory file entries.
+// Enumerates the |dir_id| directory file entries.
 //
 // Called on the UI thread to dispatch the request to the
 // MediaTransferProtocolManager.
@@ -91,7 +94,7 @@ void OpenStorageOnUIThread(
 // |success_callback| and |error_callback| runs on the IO thread.
 void ReadDirectoryOnUIThread(
     const std::string& storage_name,
-    const std::string& root,
+    uint32 dir_id,
     const base::Callback<
         void(const fileapi::AsyncFileUtil::EntryList&)>& success_callback,
     const base::Callback<void(base::File::Error)>& error_callback) {
@@ -100,7 +103,7 @@ void ReadDirectoryOnUIThread(
       GetDeviceTaskHelperForStorage(storage_name);
   if (!task_helper)
     return;
-  task_helper->ReadDirectoryByPath(root, success_callback, error_callback);
+  task_helper->ReadDirectoryById(dir_id, success_callback, error_callback);
 }
 
 // Gets the |file_path| details.
@@ -114,15 +117,15 @@ void ReadDirectoryOnUIThread(
 // |success_callback| and |error_callback| runs on the IO thread.
 void GetFileInfoOnUIThread(
     const std::string& storage_name,
-    const std::string& file_path,
-    const base::Callback<void(const base::File::Info&)>& success_callback,
-    const base::Callback<void(base::File::Error)>& error_callback) {
+    uint32 file_id,
+    const MTPDeviceAsyncDelegate::GetFileInfoSuccessCallback& success_callback,
+    const MTPDeviceAsyncDelegate::ErrorCallback& error_callback) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   MTPDeviceTaskHelper* task_helper =
       GetDeviceTaskHelperForStorage(storage_name);
   if (!task_helper)
     return;
-  task_helper->GetFileInfoByPath(file_path, success_callback, error_callback);
+  task_helper->GetFileInfoById(file_id, success_callback, error_callback);
 }
 
 // Copies the contents of |device_file_path| to |snapshot_file_path|.
@@ -188,20 +191,128 @@ void CloseStorageAndDestroyTaskHelperOnUIThread(
 }  // namespace
 
 MTPDeviceDelegateImplLinux::PendingTaskInfo::PendingTaskInfo(
+    const base::FilePath& path,
+    content::BrowserThread::ID thread_id,
     const tracked_objects::Location& location,
     const base::Closure& task)
-    : location(location),
+    : path(path),
+      thread_id(thread_id),
+      location(location),
       task(task) {
 }
 
 MTPDeviceDelegateImplLinux::PendingTaskInfo::~PendingTaskInfo() {
 }
 
+// Represents a file on the MTP device.
+// Lives on the IO thread.
+class MTPDeviceDelegateImplLinux::MTPFileNode {
+ public:
+  MTPFileNode(uint32 file_id,
+              MTPFileNode* parent,
+              FileIdToMTPFileNodeMap* file_id_to_node_map);
+  ~MTPFileNode();
+
+  const MTPFileNode* GetChild(const std::string& name) const;
+
+  void EnsureChildExists(const std::string& name, uint32 id);
+
+  // Clears all the children, except those in |children_to_keep|.
+  void ClearNonexistentChildren(
+      const std::set<std::string>& children_to_keep);
+
+  bool DeleteChild(uint32 file_id);
+
+  uint32 file_id() const { return file_id_; }
+  MTPFileNode* parent() { return parent_; }
+
+ private:
+  // Container for holding a node's children.
+  typedef base::ScopedPtrHashMap<std::string, MTPFileNode> ChildNodes;
+
+  const uint32 file_id_;
+  ChildNodes children_;
+  MTPFileNode* const parent_;
+  FileIdToMTPFileNodeMap* file_id_to_node_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(MTPFileNode);
+};
+
+MTPDeviceDelegateImplLinux::MTPFileNode::MTPFileNode(
+    uint32 file_id,
+    MTPFileNode* parent,
+    FileIdToMTPFileNodeMap* file_id_to_node_map)
+    : file_id_(file_id),
+      parent_(parent),
+      file_id_to_node_map_(file_id_to_node_map) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  DCHECK(file_id_to_node_map_);
+  DCHECK(!ContainsKey(*file_id_to_node_map_, file_id_));
+  (*file_id_to_node_map_)[file_id_] = this;
+}
+
+MTPDeviceDelegateImplLinux::MTPFileNode::~MTPFileNode() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  size_t erased = file_id_to_node_map_->erase(file_id_);
+  DCHECK_EQ(1U, erased);
+}
+
+const MTPDeviceDelegateImplLinux::MTPFileNode*
+MTPDeviceDelegateImplLinux::MTPFileNode::GetChild(
+    const std::string& name) const {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  return children_.get(name);
+}
+
+void MTPDeviceDelegateImplLinux::MTPFileNode::EnsureChildExists(
+    const std::string& name,
+    uint32 id) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  const MTPFileNode* child = GetChild(name);
+  if (child && child->file_id() == id)
+    return;
+
+  children_.set(
+      name,
+      make_scoped_ptr(new MTPFileNode(id, this, file_id_to_node_map_)));
+}
+
+void MTPDeviceDelegateImplLinux::MTPFileNode::ClearNonexistentChildren(
+    const std::set<std::string>& children_to_keep) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  std::set<std::string> children_to_erase;
+  for (ChildNodes::const_iterator it = children_.begin();
+       it != children_.end(); ++it) {
+    if (ContainsKey(children_to_keep, it->first))
+      continue;
+    children_to_erase.insert(it->first);
+  }
+  for (std::set<std::string>::iterator it = children_to_erase.begin();
+       it != children_to_erase.end(); ++it) {
+    children_.take_and_erase(*it);
+  }
+}
+
+bool MTPDeviceDelegateImplLinux::MTPFileNode::DeleteChild(uint32 file_id) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  for (ChildNodes::iterator it = children_.begin();
+       it != children_.end(); ++it) {
+    if (it->second->file_id() == file_id) {
+      children_.erase(it);
+      return true;
+    }
+  }
+  return false;
+}
+
 MTPDeviceDelegateImplLinux::MTPDeviceDelegateImplLinux(
     const std::string& device_location)
     : init_state_(UNINITIALIZED),
       task_in_progress_(false),
       device_path_(device_location),
+      root_node_(new MTPFileNode(mtpd::kRootFileId,
+                                 NULL,
+                                 &file_id_to_node_map_)),
       weak_ptr_factory_(this) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
   DCHECK(!device_path_.empty());
@@ -219,17 +330,16 @@ void MTPDeviceDelegateImplLinux::GetFileInfo(
     const ErrorCallback& error_callback) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
   DCHECK(!file_path.empty());
-  base::Closure call_closure =
-      base::Bind(&GetFileInfoOnUIThread,
-                 storage_name_,
-                 GetDeviceRelativePath(device_path_, file_path),
-                 base::Bind(&MTPDeviceDelegateImplLinux::OnDidGetFileInfo,
-                            weak_ptr_factory_.GetWeakPtr(),
-                            success_callback),
-                 base::Bind(&MTPDeviceDelegateImplLinux::HandleDeviceFileError,
-                            weak_ptr_factory_.GetWeakPtr(),
-                            error_callback));
-  EnsureInitAndRunTask(PendingTaskInfo(FROM_HERE, call_closure));
+  base::Closure closure =
+      base::Bind(&MTPDeviceDelegateImplLinux::GetFileInfoInternal,
+                 weak_ptr_factory_.GetWeakPtr(),
+                 file_path,
+                 success_callback,
+                 error_callback);
+  EnsureInitAndRunTask(PendingTaskInfo(file_path,
+                                       content::BrowserThread::IO,
+                                       FROM_HERE,
+                                       closure));
 }
 
 void MTPDeviceDelegateImplLinux::ReadDirectory(
@@ -238,23 +348,16 @@ void MTPDeviceDelegateImplLinux::ReadDirectory(
     const ErrorCallback& error_callback) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
   DCHECK(!root.empty());
-  std::string device_file_relative_path = GetDeviceRelativePath(device_path_,
-                                                                root);
-  base::Closure call_closure =
-      base::Bind(
-          &GetFileInfoOnUIThread,
-          storage_name_,
-          device_file_relative_path,
-          base::Bind(
-              &MTPDeviceDelegateImplLinux::OnDidGetFileInfoToReadDirectory,
-              weak_ptr_factory_.GetWeakPtr(),
-              device_file_relative_path,
-              success_callback,
-              error_callback),
-          base::Bind(&MTPDeviceDelegateImplLinux::HandleDeviceFileError,
-                     weak_ptr_factory_.GetWeakPtr(),
-                     error_callback));
-  EnsureInitAndRunTask(PendingTaskInfo(FROM_HERE, call_closure));
+  base::Closure closure =
+      base::Bind(&MTPDeviceDelegateImplLinux::ReadDirectoryInternal,
+                 weak_ptr_factory_.GetWeakPtr(),
+                 root,
+                 success_callback,
+                 error_callback);
+  EnsureInitAndRunTask(PendingTaskInfo(root,
+                                       content::BrowserThread::IO,
+                                       FROM_HERE,
+                                       closure));
 }
 
 void MTPDeviceDelegateImplLinux::CreateSnapshotFile(
@@ -265,26 +368,17 @@ void MTPDeviceDelegateImplLinux::CreateSnapshotFile(
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
   DCHECK(!device_file_path.empty());
   DCHECK(!local_path.empty());
-  std::string device_file_relative_path =
-      GetDeviceRelativePath(device_path_, device_file_path);
-  scoped_ptr<SnapshotRequestInfo> request_info(
-      new SnapshotRequestInfo(device_file_relative_path,
-                              local_path,
-                              success_callback,
-                              error_callback));
-  base::Closure call_closure =
-      base::Bind(
-          &GetFileInfoOnUIThread,
-          storage_name_,
-          device_file_relative_path,
-          base::Bind(
-              &MTPDeviceDelegateImplLinux::OnDidGetFileInfoToCreateSnapshotFile,
-              weak_ptr_factory_.GetWeakPtr(),
-              base::Passed(&request_info)),
-          base::Bind(&MTPDeviceDelegateImplLinux::HandleDeviceFileError,
-                     weak_ptr_factory_.GetWeakPtr(),
-                     error_callback));
-  EnsureInitAndRunTask(PendingTaskInfo(FROM_HERE, call_closure));
+  base::Closure closure =
+      base::Bind(&MTPDeviceDelegateImplLinux::CreateSnapshotFileInternal,
+                 weak_ptr_factory_.GetWeakPtr(),
+                 device_file_path,
+                 local_path,
+                 success_callback,
+                 error_callback);
+  EnsureInitAndRunTask(PendingTaskInfo(device_file_path,
+                                       content::BrowserThread::IO,
+                                       FROM_HERE,
+                                       closure));
 }
 
 bool MTPDeviceDelegateImplLinux::IsStreaming() {
@@ -298,20 +392,19 @@ void MTPDeviceDelegateImplLinux::ReadBytes(
     const ErrorCallback& error_callback) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
   DCHECK(!device_file_path.empty());
-  std::string device_file_relative_path =
-      GetDeviceRelativePath(device_path_, device_file_path);
-
-  ReadBytesRequest request(
-      device_file_relative_path, buf, offset, buf_len,
-      base::Bind(&MTPDeviceDelegateImplLinux::OnDidReadBytes,
-                 weak_ptr_factory_.GetWeakPtr(), success_callback),
-      base::Bind(&MTPDeviceDelegateImplLinux::HandleDeviceFileError,
-                 weak_ptr_factory_.GetWeakPtr(), error_callback));
-
-  base::Closure call_closure =
-      base::Bind(base::Bind(&ReadBytesOnUIThread, storage_name_, request));
-
-  EnsureInitAndRunTask(PendingTaskInfo(FROM_HERE, call_closure));
+  base::Closure closure =
+      base::Bind(&MTPDeviceDelegateImplLinux::ReadBytesInternal,
+                 weak_ptr_factory_.GetWeakPtr(),
+                 device_file_path,
+                 make_scoped_refptr(buf),
+                 offset,
+                 buf_len,
+                 success_callback,
+                 error_callback);
+  EnsureInitAndRunTask(PendingTaskInfo(device_file_path,
+                                       content::BrowserThread::IO,
+                                       FROM_HERE,
+                                       closure));
 }
 
 void MTPDeviceDelegateImplLinux::CancelPendingTasksAndDeleteDelegate() {
@@ -324,17 +417,159 @@ void MTPDeviceDelegateImplLinux::CancelPendingTasksAndDeleteDelegate() {
   delete this;
 }
 
+void MTPDeviceDelegateImplLinux::GetFileInfoInternal(
+    const base::FilePath& file_path,
+    const GetFileInfoSuccessCallback& success_callback,
+    const ErrorCallback& error_callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+
+  uint32 file_id;
+  if (CachedPathToId(file_path, &file_id)) {
+    GetFileInfoSuccessCallback success_callback_wrapper =
+        base::Bind(&MTPDeviceDelegateImplLinux::OnDidGetFileInfo,
+                   weak_ptr_factory_.GetWeakPtr(),
+                   success_callback);
+    ErrorCallback error_callback_wrapper =
+        base::Bind(&MTPDeviceDelegateImplLinux::HandleDeviceFileError,
+                   weak_ptr_factory_.GetWeakPtr(),
+                   error_callback,
+                   file_id);
+
+
+    base::Closure closure = base::Bind(&GetFileInfoOnUIThread,
+                                       storage_name_,
+                                       file_id,
+                                       success_callback_wrapper,
+                                       error_callback_wrapper);
+    EnsureInitAndRunTask(PendingTaskInfo(base::FilePath(),
+                                         content::BrowserThread::UI,
+                                         FROM_HERE,
+                                         closure));
+  } else {
+    error_callback.Run(base::File::FILE_ERROR_NOT_FOUND);
+  }
+  PendingRequestDone();
+}
+
+void MTPDeviceDelegateImplLinux::ReadDirectoryInternal(
+    const base::FilePath& root,
+    const ReadDirectorySuccessCallback& success_callback,
+    const ErrorCallback& error_callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+
+  uint32 dir_id;
+  if (CachedPathToId(root, &dir_id)) {
+    GetFileInfoSuccessCallback success_callback_wrapper =
+        base::Bind(&MTPDeviceDelegateImplLinux::OnDidGetFileInfoToReadDirectory,
+                   weak_ptr_factory_.GetWeakPtr(),
+                   dir_id,
+                   success_callback,
+                   error_callback);
+    ErrorCallback error_callback_wrapper =
+        base::Bind(&MTPDeviceDelegateImplLinux::HandleDeviceFileError,
+                   weak_ptr_factory_.GetWeakPtr(),
+                   error_callback,
+                   dir_id);
+    base::Closure closure = base::Bind(&GetFileInfoOnUIThread,
+                                       storage_name_,
+                                       dir_id,
+                                       success_callback_wrapper,
+                                       error_callback_wrapper);
+    EnsureInitAndRunTask(PendingTaskInfo(base::FilePath(),
+                                         content::BrowserThread::UI,
+                                         FROM_HERE,
+                                         closure));
+  } else {
+    error_callback.Run(base::File::FILE_ERROR_NOT_FOUND);
+  }
+  PendingRequestDone();
+}
+
+void MTPDeviceDelegateImplLinux::CreateSnapshotFileInternal(
+    const base::FilePath& device_file_path,
+    const base::FilePath& local_path,
+    const CreateSnapshotFileSuccessCallback& success_callback,
+    const ErrorCallback& error_callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+
+  uint32 file_id;
+  if (CachedPathToId(device_file_path, &file_id)) {
+    scoped_ptr<SnapshotRequestInfo> request_info(
+        new SnapshotRequestInfo(file_id,
+                                local_path,
+                                success_callback,
+                                error_callback));
+    GetFileInfoSuccessCallback success_callback_wrapper =
+        base::Bind(
+            &MTPDeviceDelegateImplLinux::OnDidGetFileInfoToCreateSnapshotFile,
+            weak_ptr_factory_.GetWeakPtr(),
+            base::Passed(&request_info));
+    ErrorCallback error_callback_wrapper =
+        base::Bind(&MTPDeviceDelegateImplLinux::HandleDeviceFileError,
+                   weak_ptr_factory_.GetWeakPtr(),
+                   error_callback,
+                   file_id);
+    base::Closure closure = base::Bind(&GetFileInfoOnUIThread,
+                                       storage_name_,
+                                       file_id,
+                                       success_callback_wrapper,
+                                       error_callback_wrapper);
+    EnsureInitAndRunTask(PendingTaskInfo(base::FilePath(),
+                                         content::BrowserThread::UI,
+                                         FROM_HERE,
+                                         closure));
+  } else {
+    error_callback.Run(base::File::FILE_ERROR_NOT_FOUND);
+  }
+  PendingRequestDone();
+}
+
+void MTPDeviceDelegateImplLinux::ReadBytesInternal(
+    const base::FilePath& device_file_path,
+    net::IOBuffer* buf, int64 offset, int buf_len,
+    const ReadBytesSuccessCallback& success_callback,
+    const ErrorCallback& error_callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+
+  uint32 file_id;
+  if (CachedPathToId(device_file_path, &file_id)) {
+    ReadBytesRequest request(
+        file_id, buf, offset, buf_len,
+        base::Bind(&MTPDeviceDelegateImplLinux::OnDidReadBytes,
+                   weak_ptr_factory_.GetWeakPtr(),
+                   success_callback),
+        base::Bind(&MTPDeviceDelegateImplLinux::HandleDeviceFileError,
+                   weak_ptr_factory_.GetWeakPtr(),
+                   error_callback,
+                   file_id));
+
+    base::Closure closure =
+        base::Bind(base::Bind(&ReadBytesOnUIThread, storage_name_, request));
+    EnsureInitAndRunTask(PendingTaskInfo(base::FilePath(),
+                                         content::BrowserThread::UI,
+                                         FROM_HERE,
+                                         closure));
+  } else {
+    error_callback.Run(base::File::FILE_ERROR_NOT_FOUND);
+  }
+  PendingRequestDone();
+}
+
 void MTPDeviceDelegateImplLinux::EnsureInitAndRunTask(
     const PendingTaskInfo& task_info) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
   if ((init_state_ == INITIALIZED) && !task_in_progress_) {
-    task_in_progress_ = true;
-    content::BrowserThread::PostTask(content::BrowserThread::UI,
-                                     task_info.location,
-                                     task_info.task);
+    RunTask(task_info);
     return;
   }
-  pending_tasks_.push(task_info);
+
+  // Only *Internal functions have empty paths. Since they are the continuation
+  // of the current running task, they get to cut in line.
+  if (task_info.path.empty())
+    pending_tasks_.push_front(task_info);
+  else
+    pending_tasks_.push_back(task_info);
+
   if (init_state_ == UNINITIALIZED) {
     init_state_ = PENDING_INIT;
     task_in_progress_ = true;
@@ -348,6 +583,29 @@ void MTPDeviceDelegateImplLinux::EnsureInitAndRunTask(
   }
 }
 
+void MTPDeviceDelegateImplLinux::RunTask(const PendingTaskInfo& task_info) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  DCHECK_EQ(INITIALIZED, init_state_);
+  DCHECK(!task_in_progress_);
+  task_in_progress_ = true;
+
+  bool need_to_check_cache = !task_info.path.empty();
+  if (need_to_check_cache) {
+    base::FilePath uncached_path =
+        NextUncachedPathComponent(task_info.path, task_info.cached_path);
+    if (!uncached_path.empty()) {
+      // Save the current task and do a cache lookup first.
+      pending_tasks_.push_front(task_info);
+      FillFileCache(uncached_path);
+      return;
+    }
+  }
+
+  content::BrowserThread::PostTask(task_info.thread_id,
+                          task_info.location,
+                          task_info.task);
+}
+
 void MTPDeviceDelegateImplLinux::WriteDataIntoSnapshotFile(
     const base::File::Info& file_info) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
@@ -355,7 +613,7 @@ void MTPDeviceDelegateImplLinux::WriteDataIntoSnapshotFile(
   DCHECK_GT(file_info.size, 0);
   DCHECK(task_in_progress_);
   SnapshotRequestInfo request_info(
-      current_snapshot_request_info_->device_file_path,
+      current_snapshot_request_info_->file_id,
       current_snapshot_request_info_->snapshot_file_path,
       base::Bind(
           &MTPDeviceDelegateImplLinux::OnDidWriteDataIntoSnapshotFile,
@@ -385,12 +643,9 @@ void MTPDeviceDelegateImplLinux::ProcessNextPendingRequest() {
   if (pending_tasks_.empty())
     return;
 
-  task_in_progress_ = true;
-  const PendingTaskInfo& task_info = pending_tasks_.front();
-  content::BrowserThread::PostTask(content::BrowserThread::UI,
-                                   task_info.location,
-                                   task_info.task);
-  pending_tasks_.pop();
+  PendingTaskInfo task_info = pending_tasks_.front();
+  pending_tasks_.pop_front();
+  RunTask(task_info);
 }
 
 void MTPDeviceDelegateImplLinux::OnInitCompleted(bool succeeded) {
@@ -408,7 +663,7 @@ void MTPDeviceDelegateImplLinux::OnDidGetFileInfo(
 }
 
 void MTPDeviceDelegateImplLinux::OnDidGetFileInfoToReadDirectory(
-    const std::string& root,
+    uint32 dir_id,
     const ReadDirectorySuccessCallback& success_callback,
     const ErrorCallback& error_callback,
     const base::File::Info& file_info) {
@@ -416,19 +671,22 @@ void MTPDeviceDelegateImplLinux::OnDidGetFileInfoToReadDirectory(
   DCHECK(task_in_progress_);
   if (!file_info.is_directory) {
     return HandleDeviceFileError(error_callback,
+                                 dir_id,
                                  base::File::FILE_ERROR_NOT_A_DIRECTORY);
   }
 
   base::Closure task_closure =
       base::Bind(&ReadDirectoryOnUIThread,
                  storage_name_,
-                 root,
+                 dir_id,
                  base::Bind(&MTPDeviceDelegateImplLinux::OnDidReadDirectory,
                             weak_ptr_factory_.GetWeakPtr(),
+                            dir_id,
                             success_callback),
                  base::Bind(&MTPDeviceDelegateImplLinux::HandleDeviceFileError,
                             weak_ptr_factory_.GetWeakPtr(),
-                            error_callback));
+                            error_callback,
+                            dir_id));
   content::BrowserThread::PostTask(content::BrowserThread::UI,
                                    FROM_HERE,
                                    task_closure);
@@ -448,7 +706,9 @@ void MTPDeviceDelegateImplLinux::OnDidGetFileInfoToCreateSnapshotFile(
     error = base::File::FILE_ERROR_FAILED;
 
   if (error != base::File::FILE_OK)
-    return HandleDeviceFileError(snapshot_request_info->error_callback, error);
+    return HandleDeviceFileError(snapshot_request_info->error_callback,
+                                 snapshot_request_info->file_id,
+                                 error);
 
   base::File::Info snapshot_file_info(file_info);
   // Modify the last modified time to null. This prevents the time stamp
@@ -465,10 +725,38 @@ void MTPDeviceDelegateImplLinux::OnDidGetFileInfoToCreateSnapshotFile(
 }
 
 void MTPDeviceDelegateImplLinux::OnDidReadDirectory(
+    uint32 dir_id,
     const ReadDirectorySuccessCallback& success_callback,
     const fileapi::AsyncFileUtil::EntryList& file_list) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
-  success_callback.Run(file_list, false /*no more entries*/);
+
+  FileIdToMTPFileNodeMap::iterator it = file_id_to_node_map_.find(dir_id);
+  DCHECK(it != file_id_to_node_map_.end());
+  MTPFileNode* dir_node = it->second;
+  std::set<std::string> children_to_keep;
+
+  fileapi::AsyncFileUtil::EntryList normalized_file_list;
+  for (size_t i = 0; i < file_list.size(); ++i) {
+    normalized_file_list.push_back(file_list[i]);
+    fileapi::DirectoryEntry& entry = normalized_file_list.back();
+
+    // |entry.name| has the file id encoded in it. Decode here.
+    size_t separator_idx = entry.name.find_last_of(',');
+    DCHECK_NE(std::string::npos, separator_idx);
+    std::string file_id_str = entry.name.substr(separator_idx);
+    file_id_str = file_id_str.substr(1);  // Get rid of the comma.
+    uint32 file_id = 0;
+    bool ret = base::StringToUint(file_id_str, &file_id);
+    DCHECK(ret);
+    entry.name = entry.name.substr(0, separator_idx);
+
+    // Refresh the in memory tree.
+    dir_node->EnsureChildExists(entry.name, file_id);
+    children_to_keep.insert(entry.name);
+  }
+  dir_node->ClearNonexistentChildren(children_to_keep);
+
+  success_callback.Run(normalized_file_list, false /*no more entries*/);
   PendingRequestDone();
 }
 
@@ -500,14 +788,111 @@ void MTPDeviceDelegateImplLinux::OnDidReadBytes(
   PendingRequestDone();
 }
 
+void MTPDeviceDelegateImplLinux::OnDidFillFileCache(
+    const base::FilePath& path,
+    const fileapi::AsyncFileUtil::EntryList& /* file_list */,
+    bool /* has_more */) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  DCHECK(path.IsParent(pending_tasks_.front().path));
+  pending_tasks_.front().cached_path = path;
+}
+
+void MTPDeviceDelegateImplLinux::OnFillFileCacheFailed(
+    base::File::Error /* error */) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  // When filling the cache fails for the task at the front of the queue, clear
+  // the path of the task so it will not try to do any more caching. Instead,
+  // the task will just run and fail the CachedPathToId() lookup.
+  pending_tasks_.front().path.clear();
+}
+
 void MTPDeviceDelegateImplLinux::HandleDeviceFileError(
     const ErrorCallback& error_callback,
+    uint32 file_id,
     base::File::Error error) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+
+  FileIdToMTPFileNodeMap::iterator it = file_id_to_node_map_.find(file_id);
+  if (it != file_id_to_node_map_.end()) {
+    MTPFileNode* parent = it->second->parent();
+    if (parent) {
+      bool ret = parent->DeleteChild(file_id);
+      DCHECK(ret);
+    }
+  }
   error_callback.Run(error);
   PendingRequestDone();
 }
 
+base::FilePath MTPDeviceDelegateImplLinux::NextUncachedPathComponent(
+    const base::FilePath& path,
+    const base::FilePath& cached_path) const {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  DCHECK(cached_path.empty() || cached_path.IsParent(path));
+
+  base::FilePath uncached_path;
+  std::string device_relpath = GetDeviceRelativePath(device_path_, path);
+  if (!device_relpath.empty() && device_relpath != kRootPath) {
+    uncached_path = device_path_;
+    std::vector<std::string> device_relpath_components;
+    base::SplitString(device_relpath, '/', &device_relpath_components);
+    DCHECK(!device_relpath_components.empty());
+    bool all_components_cached = true;
+    const MTPFileNode* current_node = root_node_.get();
+    for (size_t i = 0; i < device_relpath_components.size(); ++i) {
+      current_node = current_node->GetChild(device_relpath_components[i]);
+      if (!current_node) {
+        // With a cache miss, check if it is a genuine failure. If so, pretend
+        // the entire |path| is cached, so there is no further attempt to do
+        // more caching. The actual operation will then fail.
+        all_components_cached =
+            !cached_path.empty() && (uncached_path == cached_path);
+        break;
+      }
+      uncached_path = uncached_path.Append(device_relpath_components[i]);
+    }
+    if (all_components_cached)
+      uncached_path.clear();
+  }
+  return uncached_path;
+}
+
+void MTPDeviceDelegateImplLinux::FillFileCache(
+    const base::FilePath& uncached_path) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  DCHECK(task_in_progress_);
+
+  ReadDirectorySuccessCallback success_callback =
+      base::Bind(&MTPDeviceDelegateImplLinux::OnDidFillFileCache,
+                 weak_ptr_factory_.GetWeakPtr(),
+                 uncached_path);
+  ErrorCallback error_callback =
+      base::Bind(&MTPDeviceDelegateImplLinux::OnFillFileCacheFailed,
+                 weak_ptr_factory_.GetWeakPtr());
+  ReadDirectoryInternal(uncached_path, success_callback, error_callback);
+}
+
+
+bool MTPDeviceDelegateImplLinux::CachedPathToId(const base::FilePath& path,
+                                                uint32* id) const {
+  DCHECK(id);
+
+  std::string device_relpath = GetDeviceRelativePath(device_path_, path);
+  if (device_relpath.empty())
+    return false;
+  std::vector<std::string> device_relpath_components;
+  if (device_relpath != kRootPath)
+    base::SplitString(device_relpath, '/', &device_relpath_components);
+  const MTPFileNode* current_node = root_node_.get();
+  for (size_t i = 0; i < device_relpath_components.size(); ++i) {
+    current_node = current_node->GetChild(device_relpath_components[i]);
+    if (!current_node)
+      return false;
+  }
+  *id = current_node->file_id();
+  return true;
+}
+
 void CreateMTPDeviceAsyncDelegate(
     const std::string& device_location,
     const CreateMTPDeviceAsyncDelegateCallback& callback) {