[FileSystem] Extend file system and have it use the VFS.

[JDevlieghere]

Summary

This patch extends the FileSystem class with a bunch of operations that are currently implemented as methods of the FileSpec class.

The implementation uses the virtual file system which means that the class is now stateful. I've turned it into a singleton because:

• We need it for the shared module cache which lives above the debugger.
• Passing it around would be inconvenient as we'll need it wherever we want to manipulate a file. I also don't think passing the FS as a parameter convey any useful information from an API standpoint.

This is the first patch in a series that will remove methods manipulating the filesystem from FileSpec. As I make more changes I might have to updated it or extend it with new methods.

[labath]

Back when the FileSystem class was introduced, the idea was that *it* would eventually become the gateway to the real filesystem, and FileSpec would just deal with abstract path manipulation.

I still think that is a good idea, particularly in light of this patch. So I would propose to integrate this VFS functionality into that class, and then remove any operations that touch real files from the file spec class.

(Also, given that now about 50% of filesystem operations go through FileSpec and the other half through FileSystem (or other methods), any attempts to use FileSpec to control how filenames are interpreted will not be complete).

[JDevlieghere]

Note that there's also a File class which we'll need to patch up separately together with all other uses that actually open or read a file. For this class we can do the same as we did for FileSpec: deferring relevant operations to the FileSystem class.

[zturner]

It seems like FileSpec was moved out of Utility and into Host. I’m not a
fan of this change, because it took a lot of effort to get it into Utility,
which helped break a lot of bad dependencies. Can we invert this dependency
and move FileSpec back into Utility?

[labath]

I also think it we should try to keep FileSpec in the Utility module. We should be able to do that by deleting the "utility" functions in the FileSpec class, and updating everything to go through the FileSystem class.

After the VFS introduction, something like file_spec.Exists() will not even be well-defined anyway, as one will have to specify which file system are we checking the existence in. So, it would be more correct to say file_spec.Exists(my_vfs), at which point it's not too much of a stretch to change this into my_vfs.Exists(file_spec).

(This is the same argument I was giving earlier, since even before VFS we kinda were dealing with multiple file systems (host, remote device). In fact, after this it might be a nice cleanup to change the Platform class from vending a bunch of FS-like methods to (FileExists, Unlink, CreateSymlink, ...), to have a single getRemoteFS method returning a VFS which does the right thing "under the hood").

tl;dr: I'd propose to (in two or more patches):

• replace FileSpec "utility" methods with equivalent FileSystem functionality
• do the necessary FileSystem changes to support VFS

source/Host/common/FileSystem.cpp

26–31

replace with static FileSystem *g_fs = new FileSystem();

35–37

I'm not sure what's your use case here, but would it make more sense instead of modifying the singleton object to have more that one FileSystem instance floating around? It could be local to each Debugger (?) object and everyone would fetch it from there when needed.

[JDevlieghere]

While I don't disagree with the proposed approach, it needs to be highlighted that extracting all file system operations would be very intrusive.

• Almost all logic in FileSpec deals with the filesystem. You can't even resolve a path without it. How do you imagine this would work?
• This will significantly increase the verbosity of working with FileSpec. Depending on the solution to the previous bullet point, you might have to do something like FileSpec spec(path);FS.Resolve(spec);FS.Exists(spec).

Additionally, if we make the FileSystem a member of the debugger, we'd have to pass it everywhere we pass a FileSpec. I'm not convinced that's something we want. We could put the FileSpec and the FileSystem in a wrapper object but then we're essentially where we are today. Furthermore, for the reproducers, we need the FileSystem to live above the debugger because of the shared module cache. I can't really imagine a scenario where we'd need two debuggers with a different VFS.

[zturner]

I envision FileSpec as being more of a PathSpec. It should be able manipulate paths as strings and nothing more. There is indeed some logic that still remains that resolves paths, but it manages to do this using LLVM's file system APIs and the only reason it's still there is because it was baked in and a bit hard to remove.

One idea for removing it would be to have FileSpec FileSystem::Resolve(const FileSpec &). Then instead of saying FileSpec foo(path, /*resolve = */ true);, they could say FileSpec foo = FileSystem::Resolve(FileSpec(path)); or something.

[JDevlieghere]

Thanks for the feedback! I totally agree it's a good solution and it was one of the things I considered. It didn't make it to the top of the list because it is very intrusive and changes the semantics of FileSpec quite a bit (i.e. it becomes a PathSpec as Zachary noted). Anyway, I'm happy to do this and I'll split this up in two patches as Pavel suggested. I'll extend the FileSystem first, so that we can do the VFS stuff straight away instead of implementing these methods twice.

[zturner]

In D53532#1276463, @JDevlieghere wrote:

Thanks for the feedback! I totally agree it's a good solution and it was one of the things I considered. It didn't make it to the top of the list because it is very intrusive and changes the semantics of FileSpec quite a bit (i.e. it becomes a PathSpec as Zachary noted). Anyway, I'm happy to do this and I'll split this up in two patches as Pavel suggested. I'll extend the FileSystem first, so that we can do the VFS stuff straight away instead of implementing these methods twice.

It does change them, but that's always been the sort of "end goal" of FileSpec anyway, it just hasn't been reached yet. Hopefully we can get there with your help :)

[JDevlieghere]

I'll recycle this differential for the first patch that changes the FileSystem class.

[labath]

Now that I know your use case (I forgot that you're working on the replay now, and the mention of VFS threw me off in a completely different direction), I agree that having a single global filesystem is fine. As for the increased verbosity, I wonder if we should make the fs accessor a free function instead of a member (so that you write something like hostFS().Symlink(..) instead of FileSystem::instance().Symlink(...).

(Theoretically, we might even make the VFS instance a global variable, and then we could keep the current pattern of accessing stuff via static methods, but I like the fact that this VFS thingy could then be reused for working with files on remote devices. Also, you may need a working FS instance in the guts of the replay code, to e.g., read the replay data.)

include/lldb/Host/FileSystem.h

35

I am wondering if we could make this work without exposing the ability to change the FS implementation mid-flight to everyone. How are you planning to initialize the record/replay? Would it be possible to pass in the VFS instance via some kind of an Initialize function (and have it be immutable from that point on)?

include/lldb/Utility/FileSpec.h

423

accidental change?

[JDevlieghere]

Address Pavel's feedback:

• Change to Initialize method which can only be called once.
• Fix accidental change in comment.

[labath]

In D53532#1279022, @JDevlieghere wrote:

Address Pavel's feedback:

• Change to Initialize method which can only be called once.

I suppose this is slightly better, but what I meant was to have a static (like all other functions with the same name) Initialize function, which has to be called before the first call to Instance(). During normal startup, this could be called from SystemInitializer, but I am not sure how would that work for record/replay (that's why I was asking how you planned to initialize those). It would require to setup the record/replay machinery very early on, which may be tricky. But on the other hand, you probably want to initialize these as early as possible anyway.

Do you think something like that would be possible?

[JDevlieghere]

In D53532#1280018, @labath wrote:

In D53532#1279022, @JDevlieghere wrote:

Address Pavel's feedback:

• Change to Initialize method which can only be called once.

I suppose this is slightly better, but what I meant was to have a static (like all other functions with the same name) Initialize function, which has to be called before the first call to Instance(). During normal startup, this could be called from SystemInitializer, but I am not sure how would that work for record/replay (that's why I was asking how you planned to initialize those). It would require to setup the record/replay machinery very early on, which may be tricky. But on the other hand, you probably want to initialize these as early as possible anyway.

Do you think something like that would be possible?

Alright, I see what you mean. You know more about the architecture, but it looks like we initialize the system before even reading the command line arguments in the driver. I have to read the reproducer before I can set the appropriate file system, so I'm not sure if this is possible.

[labath]

In D53532#1280734, @JDevlieghere wrote:

In D53532#1280018, @labath wrote:

In D53532#1279022, @JDevlieghere wrote:

Address Pavel's feedback:

• Change to Initialize method which can only be called once.

I suppose this is slightly better, but what I meant was to have a static (like all other functions with the same name) Initialize function, which has to be called before the first call to Instance(). During normal startup, this could be called from SystemInitializer, but I am not sure how would that work for record/replay (that's why I was asking how you planned to initialize those). It would require to setup the record/replay machinery very early on, which may be tricky. But on the other hand, you probably want to initialize these as early as possible anyway.

Do you think something like that would be possible?

Alright, I see what you mean. You know more about the architecture, but it looks like we initialize the system before even reading the command line arguments in the driver. I have to read the reproducer before I can set the appropriate file system, so I'm not sure if this is possible.

Yes, right now it certainly seems to be the case that we parse cmdline late in the game. However, it's not clear to me whether that has to be the case.

I can't say I have thought this through to the end, but it seems to me that setting up the repro engine should be one of the first (if not THE first) SB calls from the driver. Right now the parsing happens too late (e.g. we already have an SBDebugger instance created at that point). I am not sure you could safely initialize record/replay at that point, even if you got FileSystem switching working.

Architecturally, the cleanest solution to me seems to be doing the command line parsing (even if it's just the repro-related args) before SBDebugger::Initialize, and then have special versions of the Initialize function like Initialize(args_for_record) and Initialize(args_for_replay). The interesting repro-related stuff would then happen in these functions, which can then call the Initialize functions of relevant components (like FileSystem) and pass appropriate arguments.

However, I can't say how would that fit into your intended design or any code you already have implemented.

[JDevlieghere]

In D53532#1280880, @labath wrote:

Yes, right now it certainly seems to be the case that we parse cmdline late in the game. However, it's not clear to me whether that has to be the case.

I can't say I have thought this through to the end, but it seems to me that setting up the repro engine should be one of the first (if not THE first) SB calls from the driver. Right now the parsing happens too late (e.g. we already have an SBDebugger instance created at that point). I am not sure you could safely initialize record/replay at that point, even if you got FileSystem switching working.

Architecturally, the cleanest solution to me seems to be doing the command line parsing (even if it's just the repro-related args) before SBDebugger::Initialize, and then have special versions of the Initialize function like Initialize(args_for_record) and Initialize(args_for_replay). The interesting repro-related stuff would then happen in these functions, which can then call the Initialize functions of relevant components (like FileSystem) and pass appropriate arguments.

However, I can't say how would that fit into your intended design or any code you already have implemented.

Sounds reasonable. Let's go with the static Initialize approach now and figure out the details about initializing the reproducer later.

[JDevlieghere]

Add static initializers.

[labath]

Thanks for bearing with me. I am very happy with how this turned out in the end. I have more suggestion on how to clean up the initialization, which you can incorporate if you like it, but I don't want to hold up the patch over that.

include/lldb/Host/FileSystem.h

21

Not needed anymore?

include/lldb/Utility/FileSpec.h

423

It seems this is still here... :(

source/Host/common/FileSystem.cpp

32

Instead of manual m_initialized management, what would you say to this:

• have a private InstanceImpl (or whatever) function, which returns an Optional<FileSystem> &
• Initialize does InstanceImpl().emplace(VFS); (it can check that the value is None beforehand if you want, but I am not worried about people accidentally calling Initialize twice).
• Terminate does InstanceImpl().reset();
• Instance does return *InstanceImpl();

I think this would be a bit cleaner as it would allow is to specify the VFS directly during construction. We would avoid having to construct a FileSystem object with a dummy VFS, only to replace it with another one later. And also you wouldn't need to subclass FileSystem in the unit tests just to change the implementation.

unittests/Host/FileSystemTest.cpp

295–303

You can write this more concisely (and with better error messages) as EXPECT_THAT(visited, testing::UnorderedElementsAre("/foo", "/bar", "/baz", "/qux")); (you need to include gmock.h for that to work).

include/lldb/Host/FileSystem.h

 //===-- FileSystem.h --------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef liblldb_Host_FileSystem_h
 #define liblldb_Host_FileSystem_h
 
 #include "lldb/Utility/FileSpec.h"
 #include "lldb/Utility/Status.h"
+
 #include "llvm/Support/Chrono.h"
+#include "llvm/Support/VirtualFileSystem.h"
 
 #include "lldb/lldb-types.h"
 
 #include <stdint.h>
 #include <stdio.h>
 #include <sys/stat.h>
 
 namespace lldb_private {
 class FileSystem {
 public:
   static const char *DEV_NULL;
   static const char *PATH_CONVERSION_ERROR;
 
-  static Status Symlink(const FileSpec &src, const FileSpec &dst);
-  static Status Readlink(const FileSpec &src, FileSpec &dst);
+  FileSystem() : m_fs(llvm::vfs::getRealFileSystem()) {}
+
+  static FileSystem &Instance();
+
+  void ChangeFileSystem(llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> fs);
 
-  static Status ResolveSymbolicLink(const FileSpec &src, FileSpec &dst);
+  Status Symlink(const FileSpec &src, const FileSpec &dst);
+  Status Readlink(const FileSpec &src, FileSpec &dst);
+
+  Status ResolveSymbolicLink(const FileSpec &src, FileSpec &dst);
 
   /// Wraps ::fopen in a platform-independent way. Once opened, FILEs can be
   /// manipulated and closed with the normal ::fread, ::fclose, etc. functions.
-  static FILE *Fopen(const char *path, const char *mode);
+  FILE *Fopen(const char *path, const char *mode);
+
+  /// Returns the modification time of the given file.
+  /// @{
+  llvm::sys::TimePoint<> GetModificationTime(const FileSpec &file_spec) const;
+  llvm::sys::TimePoint<> GetModificationTime(const llvm::Twine &path) const;
+  /// @}
+
+  /// Returns the on-disk size of the given file in bytes.
+  /// @{
+  uint64_t GetByteSize(const FileSpec &file_spec) const;
+  uint64_t GetByteSize(const llvm::Twine &path) const;
+  /// @}
+
+  /// Return the current permissions of the given file.
+  ///
+  /// Returns a bitmask for the current permissions of the file (zero or more
+  /// of the permission bits defined in File::Permissions).
+  /// @{
+  uint32_t GetPermissions(const FileSpec &file_spec) const;
+  uint32_t GetPermissions(const llvm::Twine &path) const;
+  /// @}
+
+  /// Returns whether the given file exists.
+  /// @{
+  bool Exists(const FileSpec &file_spec) const;
+  bool Exists(const llvm::Twine &path) const;
+  /// @}
+
+  /// Returns whether the given file is readable.
+  /// @{
+  bool Readable(const FileSpec &file_spec) const;
+  bool Readable(const llvm::Twine &path) const;
+  /// @}
+
+  /// Make the given file path absolute.
+  /// @{
+  std::error_code MakeAbsolute(llvm::SmallVectorImpl<char> &path) const;
+  std::error_code MakeAbsolute(FileSpec &file_spec) const;
+  /// @}
+
+  /// Resolve path to make it canonical.
+  /// @{
+  void Resolve(llvm::SmallVectorImpl<char> &path);
+  void Resolve(FileSpec &file_spec);
+  /// @}
+
+  enum EnumerateDirectoryResult {
+    /// Enumerate next entry in the current directory.
+    eEnumerateDirectoryResultNext,
+    /// Recurse into the current entry if it is a directory or symlink, or next
+    /// if not.
+    eEnumerateDirectoryResultEnter,
+    /// Stop directory enumerations at any level.
+    eEnumerateDirectoryResultQuit
+  };
+
+  typedef EnumerateDirectoryResult (*EnumerateDirectoryCallbackType)(
+      void *baton, llvm::sys::fs::file_type file_type, llvm::StringRef);
+
+  typedef std::function<EnumerateDirectoryResult(
+      llvm::sys::fs::file_type file_type, llvm::StringRef)>
+      DirectoryCallback;
+
+  void EnumerateDirectory(llvm::Twine path, bool find_directories,
+                          bool find_files, bool find_other,
+                          EnumerateDirectoryCallbackType callback,
+                          void *callback_baton);
+
+  std::error_code GetRealPath(const llvm::Twine &path,
+                              llvm::SmallVectorImpl<char> &output) const;
 
-  static llvm::sys::TimePoint<> GetModificationTime(const FileSpec &file_spec);
+private:
+  llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> m_fs;
 };
-}
+} // namespace lldb_private
 
 #endif

include/lldb/Utility/FileSpec.h

public:
   /// Returns true if the filespec represents an absolute path.
   ///
   /// @return
   ///     \b true if the filespec represents an absolute path,
   ///     \b false otherwise.
   //------------------------------------------------------------------
   bool IsAbsolute() const;
 
+  /// Temporary helper for FileSystem change.
+  void SetPath(llvm::StringRef p) { SetFile(p, false); }
+
   //------------------------------------------------------------------
   /// Extract the full path to the file.
   ///
   /// Extract the directory and path into a fixed buffer. This is needed as
   /// the directory and path are stored in separate string values.
   ///
   /// @param[out] path
   ///     The buffer in which to place the extracted full path.
public:
   const char *GetCString(bool denormalize = true) const;
 
   //------------------------------------------------------------------
   /// Extract the full path to the file.
   ///
   /// Extract the directory and path into an llvm::SmallVectorImpl<>
   ///
   /// @return
-  ///     Returns a std::string with the directory and filename
+  ///     Retuthe rns a std::string with the directory and filename
   ///     concatenated.
   //------------------------------------------------------------------
   void GetPath(llvm::SmallVectorImpl<char> &path,
                bool denormalize = true) const;
 
   //------------------------------------------------------------------
   /// Extract the extension of the file.
   ///

source/Core/Disassembler.cpp

 bool Instruction::TestEmulation(Stream *out_stream, const char *file_name) {
   if (!out_stream)
     return false;
 
   if (!file_name) {
     out_stream->Printf("Instruction::TestEmulation:  Missing file_name.");
     return false;
   }
-  FILE *test_file = FileSystem::Fopen(file_name, "r");
+  FILE *test_file = FileSystem::Instance().Fopen(file_name, "r");
   if (!test_file) {
     out_stream->Printf(
         "Instruction::TestEmulation: Attempt to open test file failed.");
     return false;
   }
 
   char buffer[256];
   if (!fgets(buffer, 255, test_file)) {

source/Core/Module.cpp

if (!modules_specs.FindMatchingModuleSpec(module_spec,
                                             matching_module_spec)) {
     if (log) {
       log->Printf("Found local object file but the specs didn't match");
     }
     return;
   }
 
   if (module_spec.GetFileSpec())
-    m_mod_time = FileSystem::GetModificationTime(module_spec.GetFileSpec());
+    m_mod_time = FileSystem::Instance().GetModificationTime(module_spec.GetFileSpec());
   else if (matching_module_spec.GetFileSpec())
     m_mod_time =
-        FileSystem::GetModificationTime(matching_module_spec.GetFileSpec());
+        FileSystem::Instance().GetModificationTime(matching_module_spec.GetFileSpec());
 
   // Copy the architecture from the actual spec if we got one back, else use
   // the one that was specified
   if (matching_module_spec.GetArchitecture().IsValid())
     m_arch = matching_module_spec.GetArchitecture();
   else if (module_spec.GetArchitecture().IsValid())
     m_arch = module_spec.GetArchitecture();
 
Module::Module(const ModuleSpec &module_spec)
   // specification
   m_object_offset = matching_module_spec.GetObjectOffset();
   m_object_mod_time = matching_module_spec.GetObjectModificationTime();
 }
 
 Module::Module(const FileSpec &file_spec, const ArchSpec &arch,
                const ConstString *object_name, lldb::offset_t object_offset,
                const llvm::sys::TimePoint<> &object_mod_time)
-    : m_mod_time(FileSystem::GetModificationTime(file_spec)), m_arch(arch),
+    : m_mod_time(FileSystem::Instance().GetModificationTime(file_spec)), m_arch(arch),
       m_file(file_spec), m_object_offset(object_offset),
       m_object_mod_time(object_mod_time), m_file_has_changed(false),
       m_first_file_changed_log(false) {
   // Scope for locker below...
   {
     std::lock_guard<std::recursive_mutex> guard(
         GetAllocationModuleCollectionMutex());
     GetModuleCollection().push_back(this);
SymbolVendor *Module::GetSymbolVendor(bool can_create,
   return m_symfile_ap.get();
 }
 
 void Module::SetFileSpecAndObjectName(const FileSpec &file,
                                       const ConstString &object_name) {
   // Container objects whose paths do not specify a file directly can call this
   // function to correct the file and object names.
   m_file = file;
-  m_mod_time = FileSystem::GetModificationTime(file);
+  m_mod_time = FileSystem::Instance().GetModificationTime(file);
   m_object_name = object_name;
 }
 
 const ArchSpec &Module::GetArchitecture() const { return m_arch; }
 
 std::string Module::GetSpecificationDescription() const {
   std::string spec(GetFileSpec().GetPath());
   if (m_object_name) {
if (format && format[0]) {
     }
     Host::SystemLog(Host::eSystemLogError, "%s", strm.GetData());
   }
 }
 
 bool Module::FileHasChanged() const {
   if (!m_file_has_changed)
     m_file_has_changed =
-        (FileSystem::GetModificationTime(m_file) != m_mod_time);
+        (FileSystem::Instance().GetModificationTime(m_file) != m_mod_time);
   return m_file_has_changed;
 }
 
 void Module::ReportErrorIfModifyDetected(const char *format, ...) {
   if (!m_first_file_changed_log) {
     if (FileHasChanged()) {
       m_first_file_changed_log = true;
       if (format) {

source/Core/ModuleList.cpp

if (located_binary_modulespec.GetFileSpec() != module_file_spec) {
     ModuleList matching_module_list;
     if (shared_module_list.FindModules(platform_module_spec,
                                        matching_module_list) > 0) {
       module_sp = matching_module_list.GetModuleAtIndex(0);
 
       // If we didn't have a UUID in mind when looking for the object file,
       // then we should make sure the modification time hasn't changed!
       if (platform_module_spec.GetUUIDPtr() == nullptr) {
-        auto file_spec_mod_time = FileSystem::GetModificationTime(
+        auto file_spec_mod_time = FileSystem::Instance().GetModificationTime(
             located_binary_modulespec.GetFileSpec());
         if (file_spec_mod_time != llvm::sys::TimePoint<>()) {
           if (file_spec_mod_time != module_sp->GetModificationTime()) {
             if (old_module_sp_ptr)
               *old_module_sp_ptr = module_sp;
             shared_module_list.Remove(module_sp);
             module_sp.reset();
           }

source/Core/SourceManager.cpp

if (!file_sp)
     return;
   return file_sp->FindLinesMatchingRegex(regex, start_line, end_line,
                                          match_lines);
 }
 
 SourceManager::File::File(const FileSpec &file_spec,
                           lldb::DebuggerSP debugger_sp)
     : m_file_spec_orig(file_spec), m_file_spec(file_spec),
-      m_mod_time(FileSystem::GetModificationTime(file_spec)),
+      m_mod_time(FileSystem::Instance().GetModificationTime(file_spec)),
       m_debugger_wp(debugger_sp) {
   CommonInitializer(file_spec, nullptr);
 }
 
 SourceManager::File::File(const FileSpec &file_spec, Target *target)
     : m_file_spec_orig(file_spec), m_file_spec(file_spec),
-      m_mod_time(FileSystem::GetModificationTime(file_spec)),
+      m_mod_time(FileSystem::Instance().GetModificationTime(file_spec)),
       m_debugger_wp(target ? target->GetDebugger().shared_from_this()
                            : DebuggerSP()) {
   CommonInitializer(file_spec, target);
 }
 
 void SourceManager::File::CommonInitializer(const FileSpec &file_spec,
                                             Target *target) {
   if (m_mod_time == llvm::sys::TimePoint<>()) {
if (target) {
                   test_cu_spec = sc.comp_unit;
               }
             }
           }
           if (!got_multiple) {
             SymbolContext sc;
             sc_list.GetContextAtIndex(0, sc);
             m_file_spec = sc.comp_unit;
-            m_mod_time = FileSystem::GetModificationTime(m_file_spec);
+            m_mod_time = FileSystem::Instance().GetModificationTime(m_file_spec);
           }
         }
       }
       // Try remapping if m_file_spec does not correspond to an existing file.
       if (!m_file_spec.Exists()) {
         FileSpec new_file_spec;
         // Check target specific source remappings first, then fall back to
         // modules objects can have individual path remappings that were
         // detected when the debug info for a module was found. then
         if (target->GetSourcePathMap().FindFile(m_file_spec, new_file_spec) ||
             target->GetImages().FindSourceFile(m_file_spec, new_file_spec)) {
           m_file_spec = new_file_spec;
-          m_mod_time = FileSystem::GetModificationTime(m_file_spec);
+          m_mod_time = FileSystem::Instance().GetModificationTime(m_file_spec);
         }
       }
     }
   }
 
   if (m_mod_time != llvm::sys::TimePoint<>())
     m_data_sp = DataBufferLLVM::CreateFromPath(m_file_spec.GetPath());
 }
if (CalculateLineOffsets(line))
     return line < m_offsets.size();
   return false;
 }
 
 void SourceManager::File::UpdateIfNeeded() {
   // TODO: use host API to sign up for file modifications to anything in our
   // source cache and only update when we determine a file has been updated.
   // For now we check each time we want to display info for the file.
-  auto curr_mod_time = FileSystem::GetModificationTime(m_file_spec);
+  auto curr_mod_time = FileSystem::Instance().GetModificationTime(m_file_spec);
 
   if (curr_mod_time != llvm::sys::TimePoint<>() &&
       m_mod_time != curr_mod_time) {
     m_mod_time = curr_mod_time;
     m_data_sp = DataBufferLLVM::CreateFromPath(m_file_spec.GetPath());
     m_offsets.clear();
   }
 }

source/Host/common/FileSystem.cpp

 //===-- FileSystem.cpp ------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "lldb/Host/FileSystem.h"
 
+#include "lldb/Utility/TildeExpressionResolver.h"
+
 #include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Threading.h"
 
 #include <algorithm>
 #include <fstream>
 #include <vector>
 
 using namespace lldb;
 using namespace lldb_private;
+using namespace llvm;
+
+FileSystem &FileSystem::Instance() {
+  static FileSystem g_fs;
+  return g_fs;
+}
+
+void FileSystem::ChangeFileSystem(IntrusiveRefCntPtr<vfs::FileSystem> fs) {
+  m_fs = fs;
+}
+
+sys::TimePoint<>
+FileSystem::GetModificationTime(const FileSpec &file_spec) const {
+  return GetModificationTime(file_spec.GetPath());
+}
+
+sys::TimePoint<> FileSystem::GetModificationTime(const Twine &path) const {
+  ErrorOr<vfs::Status> status = m_fs->status(path);
+  if (!status)
+    return sys::TimePoint<>();
+  return status->getLastModificationTime();
+}
+
+uint64_t FileSystem::GetByteSize(const FileSpec &file_spec) const {
+  return GetByteSize(file_spec.GetPath());
+}
+
+uint64_t FileSystem::GetByteSize(const Twine &path) const {
+  ErrorOr<vfs::Status> status = m_fs->status(path);
+  if (!status)
+    return 0;
+  return status->getSize();
+}
+
+uint32_t FileSystem::GetPermissions(const FileSpec &file_spec) const {
+  return GetPermissions(file_spec.GetPath());
+}
+
+uint32_t FileSystem::GetPermissions(const Twine &path) const {
+  ErrorOr<vfs::Status> status = m_fs->status(path);
+  if (!status)
+    return sys::fs::perms::perms_not_known;
+  return status->getPermissions();
+}
+
+bool FileSystem::Exists(const Twine &path) const { return m_fs->exists(path); }
+
+bool FileSystem::Exists(const FileSpec &file_spec) const {
+  return Exists(file_spec.GetPath());
+}
+
+bool FileSystem::Readable(const Twine &path) const {
+  return GetPermissions(path) & sys::fs::perms::all_read;
+}
+
+bool FileSystem::Readable(const FileSpec &file_spec) const {
+  return Readable(file_spec.GetPath());
+}
+
+void FileSystem::EnumerateDirectory(Twine path, bool find_directories,
+                                    bool find_files, bool find_other,
+                                    EnumerateDirectoryCallbackType callback,
+                                    void *callback_baton) {
+  std::error_code EC;
+  vfs::recursive_directory_iterator Iter(*m_fs, path, EC);
+  vfs::recursive_directory_iterator End;
+  for (; Iter != End && !EC; Iter.increment(EC)) {
+    const auto &Item = *Iter;
+    ErrorOr<vfs::Status> Status = m_fs->status(Item.path());
+    if (!Status)
+      break;
+    if (!find_files && Status->isRegularFile())
+      continue;
+    if (!find_directories && Status->isDirectory())
+      continue;
+    if (!find_other && Status->isOther())
+      continue;
+
+    auto Result = callback(callback_baton, Status->getType(), Item.path());
+    if (Result == eEnumerateDirectoryResultQuit)
+      return;
+    if (Result == eEnumerateDirectoryResultNext) {
+      // Default behavior is to recurse. Opt out if the callback doesn't want
+      // this behavior.
+      Iter.no_push();
+    }
+  }
+}
+
+std::error_code FileSystem::MakeAbsolute(SmallVectorImpl<char> &path) const {
+  return m_fs->makeAbsolute(path);
+}
+
+std::error_code FileSystem::MakeAbsolute(FileSpec &file_spec) const {
+  SmallString<128> path;
+  file_spec.GetPath(path, false);
+
+  auto EC = MakeAbsolute(path);
+  if (EC)
+    return EC;
+
+  FileSpec new_file_spec(path, false, file_spec.GetPathStyle());
+  file_spec = new_file_spec;
+  return {};
+}
+
+std::error_code FileSystem::GetRealPath(const Twine &path,
+                                        SmallVectorImpl<char> &output) const {
+  return m_fs->getRealPath(path, output);
+}
+
+void FileSystem::Resolve(SmallVectorImpl<char> &path) {
+  if (path.empty())
+    return;
+
+  // Resolve tilde.
+  SmallString<128> original_path(path.begin(), path.end());
+  StandardTildeExpressionResolver Resolver;
+  Resolver.ResolveFullPath(original_path, path);
+
+  // Try making the path absolute if it exists.
+  SmallString<128> absolute_path(path.begin(), path.end());
+  MakeAbsolute(path);
+  if (!Exists(path)) {
+    path.clear();
+    path.append(original_path.begin(), original_path.end());
+  }
+}
+
+void FileSystem::Resolve(FileSpec &file_spec) {
+  // Extract path from the FileSpec.
+  SmallString<128> path;
+  file_spec.GetPath(path);
+
+  // Resolve the path.
+  Resolve(path);
 
-llvm::sys::TimePoint<>
-FileSystem::GetModificationTime(const FileSpec &file_spec) {
-  llvm::sys::fs::file_status status;
-  std::error_code ec = llvm::sys::fs::status(file_spec.GetPath(), status);
-  if (ec)
-    return llvm::sys::TimePoint<>();
-  return status.getLastModificationTime();
+  // Update the FileSpec with the resolved path.
+  file_spec.SetPath(path);
 }

source/Host/common/HostInfoBase.cpp

bool HostInfoBase::ComputeSharedLibraryDirectory(FileSpec &file_spec) {
   // On other posix systems, we will get .../lib(64|32)?/liblldb.so.
 
   FileSpec lldb_file_spec(Host::GetModuleFileSpecForHostAddress(
       reinterpret_cast<void *>(reinterpret_cast<intptr_t>(
           HostInfoBase::ComputeSharedLibraryDirectory))));
 
   // This is necessary because when running the testsuite the shlib might be a
   // symbolic link inside the Python resource dir.
-  FileSystem::ResolveSymbolicLink(lldb_file_spec, lldb_file_spec);
+  FileSystem::Instance().ResolveSymbolicLink(lldb_file_spec, lldb_file_spec);
 
   // Remove the filename so that this FileSpec only represents the directory.
   file_spec.GetDirectory() = lldb_file_spec.GetDirectory();
 
   return (bool)file_spec.GetDirectory();
 }
 
 bool HostInfoBase::ComputeSupportExeDirectory(FileSpec &file_spec) {

source/Host/common/Symbols.cpp

FileSpec Symbols::LocateExecutableSymbolFile(const ModuleSpec &module_spec) {
   const char *symbol_filename = symbol_file_spec.GetFilename().AsCString();
   if (symbol_filename && symbol_filename[0]) {
     FileSpecList debug_file_search_paths(
         Target::GetDefaultDebugFileSearchPaths());
 
     // Add module directory.
     FileSpec module_file_spec = module_spec.GetFileSpec();
     // We keep the unresolved pathname if it fails.
-    FileSystem::ResolveSymbolicLink(module_file_spec, module_file_spec);
+    FileSystem::Instance().ResolveSymbolicLink(module_file_spec, module_file_spec);
 
     const ConstString &file_dir = module_file_spec.GetDirectory();
     debug_file_search_paths.AppendIfUnique(
         FileSpec(file_dir.AsCString("."), true));
 
     // Add current working directory.
     debug_file_search_paths.AppendIfUnique(FileSpec(".", true));
 

source/Host/posix/HostProcessPosix.cpp

Status HostProcessPosix::GetMainModule(FileSpec &file_spec) const {
 
   // Use special code here because proc/[pid]/exe is a symbolic link.
   char link_path[PATH_MAX];
   if (snprintf(link_path, PATH_MAX, "/proc/%" PRIu64 "/exe", m_process) != 1) {
     error.SetErrorString("Unable to build /proc/<pid>/exe string");
     return error;
   }
 
-  error = FileSystem::Readlink(FileSpec{link_path, false}, file_spec);
+  error = FileSystem::Instance().Readlink(FileSpec{link_path, false}, file_spec);
   if (!error.Success())
     return error;
 
   // If the binary has been deleted, the link name has " (deleted)" appended.
   // Remove if there.
   if (file_spec.GetFilename().GetStringRef().endswith(" (deleted)")) {
     const char *filename = file_spec.GetFilename().GetCString();
     static const size_t deleted_len = strlen(" (deleted)");

source/Interpreter/OptionValueFileSpec.cpp

size_t OptionValueFileSpec::AutoComplete(CommandInterpreter &interpreter,
   request.SetWordComplete(false);
   CommandCompletions::InvokeCommonCompletionCallbacks(
       interpreter, m_completion_mask, request, nullptr);
   return request.GetNumberOfMatches();
 }
 
 const lldb::DataBufferSP &OptionValueFileSpec::GetFileContents() {
   if (m_current_value) {
-    const auto file_mod_time = FileSystem::GetModificationTime(m_current_value);
+    const auto file_mod_time = FileSystem::Instance().GetModificationTime(m_current_value);
     if (m_data_sp && m_data_mod_time == file_mod_time)
       return m_data_sp;
     m_data_sp = DataBufferLLVM::CreateFromPath(m_current_value.GetPath());
     m_data_mod_time = file_mod_time;
   }
   return m_data_sp;
 }

source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.cpp

ModuleSP DynamicLoaderDarwin::FindTargetModuleForImageInfo(
   module_spec.GetUUID() = image_info.uuid;
   ModuleSP module_sp(target_images.FindFirstModule(module_spec));
 
   if (module_sp && !module_spec.GetUUID().IsValid() &&
       !module_sp->GetUUID().IsValid()) {
     // No UUID, we must rely upon the cached module modification time and the
     // modification time of the file on disk
     if (module_sp->GetModificationTime() !=
-        FileSystem::GetModificationTime(module_sp->GetFileSpec()))
+        FileSystem::Instance().GetModificationTime(module_sp->GetFileSpec()))
       module_sp.reset();
   }
 
   if (!module_sp) {
     if (can_create) {
       module_sp = target.GetSharedModule(module_spec);
       if (!module_sp || module_sp->GetObjectFile() == NULL)
         module_sp = m_process->ReadModuleFromMemory(image_info.file_spec,

source/Plugins/ObjectContainer/BSD-Archive/ObjectContainerBSDArchive.cpp

size_t ObjectContainerBSDArchive::GetModuleSpecifications(
   // see if the magic bytes match and if they do, read the entire table of
   // contents for the archive and cache it
   DataExtractor data;
   data.SetData(data_sp, data_offset, data_sp->GetByteSize());
   if (!file || !data_sp || !ObjectContainerBSDArchive::MagicBytesMatch(data))
     return 0;
 
   const size_t initial_count = specs.GetSize();
-  llvm::sys::TimePoint<> file_mod_time = FileSystem::GetModificationTime(file);
+  llvm::sys::TimePoint<> file_mod_time = FileSystem::Instance().GetModificationTime(file);
   Archive::shared_ptr archive_sp(
       Archive::FindCachedArchive(file, ArchSpec(), file_mod_time, file_offset));
   bool set_archive_arch = false;
   if (!archive_sp) {
     set_archive_arch = true;
     data_sp =
         DataBufferLLVM::CreateSliceFromPath(file.GetPath(), file_size, file_offset);
     if (data_sp) {

source/Plugins/Platform/Android/AdbClient.cpp

Status AdbClient::SyncService::internalPushFile(const FileSpec &local_file,
   char chunk[kMaxPushData];
   while (!src.eof() && !src.read(chunk, kMaxPushData).bad()) {
     size_t chunk_size = src.gcount();
     error = SendSyncRequest(kDATA, chunk_size, chunk);
     if (error.Fail())
       return Status("Failed to send file chunk: %s", error.AsCString());
   }
   error = SendSyncRequest(
-      kDONE, llvm::sys::toTimeT(FileSystem::GetModificationTime(local_file)),
+      kDONE, llvm::sys::toTimeT(FileSystem::Instance().GetModificationTime(local_file)),
       nullptr);
   if (error.Fail())
     return error;
 
   std::string response_id;
   uint32_t data_len;
   error = ReadSyncHeader(response_id, data_len);
   if (error.Fail())

source/Plugins/Platform/POSIX/PlatformPOSIX.cpp

lldb::user_id_t PlatformPOSIX::GetFileSize(const FileSpec &file_spec) {
   } else if (m_remote_platform_sp)
     return m_remote_platform_sp->GetFileSize(file_spec);
   else
     return Platform::GetFileSize(file_spec);
 }
 
 Status PlatformPOSIX::CreateSymlink(const FileSpec &src, const FileSpec &dst) {
   if (IsHost())
-    return FileSystem::Symlink(src, dst);
+    return FileSystem::Instance().Symlink(src, dst);
   else if (m_remote_platform_sp)
     return m_remote_platform_sp->CreateSymlink(src, dst);
   else
     return Platform::CreateSymlink(src, dst);
 }
 
 bool PlatformPOSIX::GetFileExists(const FileSpec &file_spec) {
   if (IsHost())

source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerCommon.cpp

 GDBRemoteCommunication::PacketResult
 GDBRemoteCommunicationServerCommon::Handle_vFile_symlink(
     StringExtractorGDBRemote &packet) {
   packet.SetFilePos(::strlen("vFile:symlink:"));
   std::string dst, src;
   packet.GetHexByteStringTerminatedBy(dst, ',');
   packet.GetChar(); // Skip ',' char
   packet.GetHexByteString(src);
-  Status error = FileSystem::Symlink(FileSpec{src, true}, FileSpec{dst, false});
+  Status error = FileSystem::Instance().Symlink(FileSpec{src, true}, FileSpec{dst, false});
   StreamString response;
   response.Printf("F%u,%u", error.GetError(), error.GetError());
   return SendPacketNoLock(response.GetString());
 }
 
 GDBRemoteCommunication::PacketResult
 GDBRemoteCommunicationServerCommon::Handle_vFile_unlink(
     StringExtractorGDBRemote &packet) {

source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

if (!is_symlink)
     return local_spec;
 
   namespace fs = llvm::sys::fs;
   if (fs::get_file_type(local_spec.GetPath(), false) !=
       fs::file_type::symlink_file)
     return local_spec;
 
   FileSpec resolved_symlink;
-  const auto error = FileSystem::Readlink(local_spec, resolved_symlink);
+  const auto error = FileSystem::Instance().Readlink(local_spec, resolved_symlink);
   if (error.Success())
     return resolved_symlink;
 
   return local_spec;
 }
 
 DWARFUnit *SymbolFileDWARF::GetBaseCompileUnit() {
   return nullptr;

source/Plugins/SymbolFile/DWARF/SymbolFileDWARFDebugMap.cpp

if (pos != m_oso_map.end()) {
       ObjectFile *obj_file = GetObjectFile();
       comp_unit_info->oso_sp.reset(new OSOInfo());
       m_oso_map[{comp_unit_info->oso_path, comp_unit_info->oso_mod_time}] =
           comp_unit_info->oso_sp;
       const char *oso_path = comp_unit_info->oso_path.GetCString();
       FileSpec oso_file(oso_path, false);
       ConstString oso_object;
       if (oso_file.Exists()) {
-        auto oso_mod_time = FileSystem::GetModificationTime(oso_file);
+        auto oso_mod_time = FileSystem::Instance().GetModificationTime(oso_file);
         if (oso_mod_time != comp_unit_info->oso_mod_time) {
           obj_file->GetModule()->ReportError(
               "debug map object file '%s' has changed (actual time is "
               "%s, debug map time is %s"
               ") since this executable was linked, file will be ignored",
               oso_file.GetPath().c_str(), llvm::to_string(oso_mod_time).c_str(),
               llvm::to_string(comp_unit_info->oso_mod_time).c_str());
           return NULL;

source/Target/Platform.cpp

RecurseCopy_Callback(void *baton, llvm::sys::fs::file_type ft,
   case fs::file_type::symlink_file: {
     // copy the file and keep going
     FileSpec dst_file = rc_baton->dst;
     if (!dst_file.GetFilename())
       dst_file.GetFilename() = src.GetFilename();
 
     FileSpec src_resolved;
 
-    rc_baton->error = FileSystem::Readlink(src, src_resolved);
+    rc_baton->error = FileSystem::Instance().Readlink(src, src_resolved);
 
     if (rc_baton->error.Fail())
       return FileSpec::eEnumerateDirectoryResultQuit; // got an error, bail out
 
     rc_baton->error =
         rc_baton->platform_ptr->CreateSymlink(dst_file, src_resolved);
 
     if (rc_baton->error.Fail())
if (GetSupportsRSync()) {
     case fs::file_type::regular_file:
       llvm::sys::fs::remove(fixed_dst.GetPath());
       error = PutFile(src, fixed_dst);
       break;
 
     case fs::file_type::symlink_file: {
       llvm::sys::fs::remove(fixed_dst.GetPath());
       FileSpec src_resolved;
-      error = FileSystem::Readlink(src, src_resolved);
+      error = FileSystem::Instance().Readlink(src, src_resolved);
       if (error.Success())
         error = CreateSymlink(dst, src_resolved);
     } break;
     case fs::file_type::fifo_file:
       error.SetErrorString("platform install doesn't handle pipes");
       break;
     case fs::file_type::socket_file:
       error.SetErrorString("platform install doesn't handle sockets");

unittests/Host/FileSystemTest.cpp

 //===-- FileSystemTest.cpp --------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "gtest/gtest.h"
 
 #include "lldb/Host/FileSystem.h"
+#include "llvm/Support/Errc.h"
 
 extern const char *TestMainArgv0;
 
 using namespace lldb_private;
+using namespace llvm;
+using llvm::sys::fs::UniqueID;
+
+// Modified from llvm/unittests/Support/VirtualFileSystemTest.cpp
+namespace {
+struct DummyFile : public vfs::File {
+  vfs::Status S;
+  explicit DummyFile(vfs::Status S) : S(S) {}
+  llvm::ErrorOr<vfs::Status> status() override { return S; }
+  llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>
+  getBuffer(const Twine &Name, int64_t FileSize, bool RequiresNullTerminator,
+            bool IsVolatile) override {
+    llvm_unreachable("unimplemented");
+  }
+  std::error_code close() override { return std::error_code(); }
+};
+
+class DummyFileSystem : public vfs::FileSystem {
+  int FSID;   // used to produce UniqueIDs
+  int FileID; // used to produce UniqueIDs
+  std::string cwd;
+  std::map<std::string, vfs::Status> FilesAndDirs;
+
+  static int getNextFSID() {
+    static int Count = 0;
+    return Count++;
+  }
+
+public:
+  DummyFileSystem() : FSID(getNextFSID()), FileID(0) {}
+
+  ErrorOr<vfs::Status> status(const Twine &Path) override {
+    std::map<std::string, vfs::Status>::iterator I =
+        FilesAndDirs.find(Path.str());
+    if (I == FilesAndDirs.end())
+      return make_error_code(llvm::errc::no_such_file_or_directory);
+    return I->second;
+  }
+  ErrorOr<std::unique_ptr<vfs::File>>
+  openFileForRead(const Twine &Path) override {
+    auto S = status(Path);
+    if (S)
+      return std::unique_ptr<vfs::File>(new DummyFile{*S});
+    return S.getError();
+  }
+  llvm::ErrorOr<std::string> getCurrentWorkingDirectory() const override {
+    return cwd;
+  }
+  std::error_code setCurrentWorkingDirectory(const Twine &Path) override {
+    cwd = Path.str();
+    return std::error_code();
+  }
+  // Map any symlink to "/symlink".
+  std::error_code getRealPath(const Twine &Path,
+                              SmallVectorImpl<char> &Output) const override {
+    auto I = FilesAndDirs.find(Path.str());
+    if (I == FilesAndDirs.end())
+      return make_error_code(llvm::errc::no_such_file_or_directory);
+    if (I->second.isSymlink()) {
+      Output.clear();
+      Twine("/symlink").toVector(Output);
+      return std::error_code();
+    }
+    Output.clear();
+    Path.toVector(Output);
+    return std::error_code();
+  }
+
+  struct DirIterImpl : public llvm::vfs::detail::DirIterImpl {
+    std::map<std::string, vfs::Status> &FilesAndDirs;
+    std::map<std::string, vfs::Status>::iterator I;
+    std::string Path;
+    bool isInPath(StringRef S) {
+      if (Path.size() < S.size() && S.find(Path) == 0) {
+        auto LastSep = S.find_last_of('/');
+        if (LastSep == Path.size() || LastSep == Path.size() - 1)
+          return true;
+      }
+      return false;
+    }
+    DirIterImpl(std::map<std::string, vfs::Status> &FilesAndDirs,
+                const Twine &_Path)
+        : FilesAndDirs(FilesAndDirs), I(FilesAndDirs.begin()),
+          Path(_Path.str()) {
+      for (; I != FilesAndDirs.end(); ++I) {
+        if (isInPath(I->first)) {
+          CurrentEntry =
+              vfs::directory_entry(I->second.getName(), I->second.getType());
+          break;
+        }
+      }
+    }
+    std::error_code increment() override {
+      ++I;
+      for (; I != FilesAndDirs.end(); ++I) {
+        if (isInPath(I->first)) {
+          CurrentEntry =
+              vfs::directory_entry(I->second.getName(), I->second.getType());
+          break;
+        }
+      }
+      if (I == FilesAndDirs.end())
+        CurrentEntry = vfs::directory_entry();
+      return std::error_code();
+    }
+  };
+
+  vfs::directory_iterator dir_begin(const Twine &Dir,
+                                    std::error_code &EC) override {
+    return vfs::directory_iterator(
+        std::make_shared<DirIterImpl>(FilesAndDirs, Dir));
+  }
+
+  void addEntry(StringRef Path, const vfs::Status &Status) {
+    FilesAndDirs[Path] = Status;
+  }
+
+  void addRegularFile(StringRef Path, sys::fs::perms Perms = sys::fs::all_all) {
+    vfs::Status S(Path, UniqueID(FSID, FileID++),
+                  std::chrono::system_clock::now(), 0, 0, 1024,
+                  sys::fs::file_type::regular_file, Perms);
+    addEntry(Path, S);
+  }
+
+  void addDirectory(StringRef Path, sys::fs::perms Perms = sys::fs::all_all) {
+    vfs::Status S(Path, UniqueID(FSID, FileID++),
+                  std::chrono::system_clock::now(), 0, 0, 0,
+                  sys::fs::file_type::directory_file, Perms);
+    addEntry(Path, S);
+  }
+
+  void addSymlink(StringRef Path) {
+    vfs::Status S(Path, UniqueID(FSID, FileID++),
+                  std::chrono::system_clock::now(), 0, 0, 0,
+                  sys::fs::file_type::symlink_file, sys::fs::all_all);
+    addEntry(Path, S);
+  }
+};
+} // namespace
 
 TEST(FileSystemTest, FileAndDirectoryComponents) {
   using namespace std::chrono;
 
   const bool resolve = true;
 #ifdef _WIN32
   FileSpec fs1("C:\\FILE\\THAT\\DOES\\NOT\\EXIST.TXT", !resolve);
 #else
   FileSpec fs1("/file/that/does/not/exist.txt", !resolve);
 #endif
   FileSpec fs2(TestMainArgv0, resolve);
 
-  EXPECT_EQ(system_clock::time_point(), FileSystem::GetModificationTime(fs1));
+  FileSystem fs;
+
+  EXPECT_EQ(system_clock::time_point(), fs.GetModificationTime(fs1));
   EXPECT_LT(system_clock::time_point() + hours(24 * 365 * 20),
-            FileSystem::GetModificationTime(fs2));
+            fs.GetModificationTime(fs2));
+}
+
+static IntrusiveRefCntPtr<DummyFileSystem> GetSimpleDummyFS() {
+  IntrusiveRefCntPtr<DummyFileSystem> D(new DummyFileSystem());
+  D->addRegularFile("/foo");
+  D->addDirectory("/bar");
+  D->addSymlink("/baz");
+  D->addRegularFile("/qux", ~sys::fs::perms::all_read);
+  D->setCurrentWorkingDirectory("/");
+  return D;
+}
+
+TEST(FileSystemTest, Exists) {
+  FileSystem fs;
+  fs.ChangeFileSystem(GetSimpleDummyFS());
+
+  EXPECT_TRUE(fs.Exists("/foo"));
+  EXPECT_TRUE(fs.Exists(FileSpec("/foo", false, FileSpec::Style::posix)));
+}
+
+TEST(FileSystemTest, Readable) {
+  FileSystem fs;
+  fs.ChangeFileSystem(GetSimpleDummyFS());
+
+  EXPECT_TRUE(fs.Readable("/foo"));
+  EXPECT_TRUE(fs.Readable(FileSpec("/foo", false, FileSpec::Style::posix)));
+
+  EXPECT_FALSE(fs.Readable("/qux"));
+  EXPECT_FALSE(fs.Readable(FileSpec("/qux", false, FileSpec::Style::posix)));
+}
+
+TEST(FileSystemTest, GetByteSize) {
+  FileSystem fs;
+  fs.ChangeFileSystem(GetSimpleDummyFS());
+
+  EXPECT_EQ((uint64_t)1024, fs.GetByteSize("/foo"));
+  EXPECT_EQ((uint64_t)1024,
+            fs.GetByteSize(FileSpec("/foo", false, FileSpec::Style::posix)));
+}
+
+TEST(FileSystemTest, GetPermissions) {
+  FileSystem fs;
+  fs.ChangeFileSystem(GetSimpleDummyFS());
+
+  EXPECT_EQ(sys::fs::all_all, fs.GetPermissions("/foo"));
+  EXPECT_EQ(sys::fs::all_all,
+            fs.GetPermissions(FileSpec("/foo", false, FileSpec::Style::posix)));
+}
+
+TEST(FileSystemTest, MakeAbsolute) {
+  FileSystem fs;
+  fs.ChangeFileSystem(GetSimpleDummyFS());
+
+  {
+    StringRef foo_relative = "foo";
+    SmallString<16> foo(foo_relative);
+    auto EC = fs.MakeAbsolute(foo);
+    EXPECT_FALSE(EC);
+    EXPECT_TRUE(foo.equals("/foo"));
+  }
+
+  {
+    FileSpec file_spec("foo", false);
+    auto EC = fs.MakeAbsolute(file_spec);
+    EXPECT_FALSE(EC);
+    EXPECT_EQ("/foo", file_spec.GetPath());
+  }
+}
+
+TEST(FileSystemTest, Resolve) {
+  FileSystem fs;
+  fs.ChangeFileSystem(GetSimpleDummyFS());
+
+  {
+    StringRef foo_relative = "foo";
+    SmallString<16> foo(foo_relative);
+    fs.Resolve(foo);
+    EXPECT_TRUE(foo.equals("/foo"));
+  }
+
+  {
+    FileSpec file_spec("foo", false);
+    fs.Resolve(file_spec);
+    EXPECT_EQ("/foo", file_spec.GetPath());
+  }
+
+  {
+    StringRef foo_relative = "bogus";
+    SmallString<16> foo(foo_relative);
+    fs.Resolve(foo);
+    EXPECT_TRUE(foo.equals("bogus"));
+  }
+
+  {
+    FileSpec file_spec("bogus", false);
+    fs.Resolve(file_spec);
+    EXPECT_EQ("bogus", file_spec.GetPath());
+  }
+}
+
+FileSystem::EnumerateDirectoryResult
+VFSCallback(void *baton, llvm::sys::fs::file_type file_type,
+            llvm::StringRef path) {
+  auto visited = static_cast<std::vector<std::string> *>(baton);
+  visited->push_back(path.str());
+  return FileSystem::eEnumerateDirectoryResultNext;
+}
+
+TEST(FileSystemTest, EnumerateDirectory) {
+  FileSystem fs;
+  fs.ChangeFileSystem(GetSimpleDummyFS());
+
+  std::vector<std::string> visited;
+
+  constexpr bool find_directories = true;
+  constexpr bool find_files = true;
+  constexpr bool find_other = true;
+
+  fs.EnumerateDirectory("/", find_directories, find_files, find_other,
+                        VFSCallback, &visited);
+
+  EXPECT_EQ(visited.size(), (size_t)4);
+  EXPECT_TRUE(std::find(visited.begin(), visited.end(), "/foo") !=
+              visited.end());
+  EXPECT_TRUE(std::find(visited.begin(), visited.end(), "/bar") !=
+              visited.end());
+  EXPECT_TRUE(std::find(visited.begin(), visited.end(), "/baz") !=
+              visited.end());
+  EXPECT_TRUE(std::find(visited.begin(), visited.end(), "/qux") !=
+              visited.end());
 }