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//===--- FileManager.cpp - File System Probing and Caching ----------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file implements the FileManager interface.
// TODO: This should index all interesting directories with dirent calls.
// getdirentries ?
// opendir/readdir_r/closedir ?
#include "clang/Basic/FileManager.h"
#include "clang/Basic/FileSystemStatCache.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <climits>
#include <cstdint>
#include <cstdlib>
#include <string>
#include <utility>
using namespace clang;
#define DEBUG_TYPE "file-search"
ALWAYS_ENABLED_STATISTIC(NumDirLookups, "Number of directory lookups.");
ALWAYS_ENABLED_STATISTIC(NumFileLookups, "Number of file lookups.");
"Number of directory cache misses.");
ALWAYS_ENABLED_STATISTIC(NumFileCacheMisses, "Number of file cache misses.");
// Common logic.
FileManager::FileManager(const FileSystemOptions &FSO,
IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS)
: FS(std::move(FS)), FileSystemOpts(FSO), SeenDirEntries(64),
SeenFileEntries(64), NextFileUID(0) {
// If the caller doesn't provide a virtual file system, just grab the real
// file system.
if (!this->FS)
this->FS = llvm::vfs::getRealFileSystem();
FileManager::~FileManager() = default;
void FileManager::setStatCache(std::unique_ptr<FileSystemStatCache> statCache) {
assert(statCache && "No stat cache provided?");
StatCache = std::move(statCache);
void FileManager::clearStatCache() { StatCache.reset(); }
/// Retrieve the directory that the given file name resides in.
/// Filename can point to either a real file or a virtual file.
static llvm::Expected<DirectoryEntryRef>
getDirectoryFromFile(FileManager &FileMgr, StringRef Filename,
bool CacheFailure) {
if (Filename.empty())
return llvm::errorCodeToError(
if (llvm::sys::path::is_separator(Filename[Filename.size() - 1]))
return llvm::errorCodeToError(make_error_code(std::errc::is_a_directory));
StringRef DirName = llvm::sys::path::parent_path(Filename);
// Use the current directory if file has no path component.
if (DirName.empty())
DirName = ".";
return FileMgr.getDirectoryRef(DirName, CacheFailure);
/// Add all ancestors of the given path (pointing to either a file or
/// a directory) as virtual directories.
void FileManager::addAncestorsAsVirtualDirs(StringRef Path) {
StringRef DirName = llvm::sys::path::parent_path(Path);
if (DirName.empty())
DirName = ".";
auto &NamedDirEnt = *SeenDirEntries.insert(
{DirName, std::errc::no_such_file_or_directory}).first;
// When caching a virtual directory, we always cache its ancestors
// at the same time. Therefore, if DirName is already in the cache,
// we don't need to recurse as its ancestors must also already be in
// the cache (or it's a known non-virtual directory).
if (NamedDirEnt.second)
// Add the virtual directory to the cache.
auto *UDE = new (DirsAlloc.Allocate()) DirectoryEntry();
UDE->Name = NamedDirEnt.first();
NamedDirEnt.second = *UDE;
// Recursively add the other ancestors.
FileManager::getDirectoryRef(StringRef DirName, bool CacheFailure) {
// stat doesn't like trailing separators except for root directory.
// At least, on Win32 MSVCRT, stat() cannot strip trailing '/'.
// (though it can strip '\\')
if (DirName.size() > 1 &&
DirName != llvm::sys::path::root_path(DirName) &&
DirName = DirName.substr(0, DirName.size()-1);
Optional<std::string> DirNameStr;
if (is_style_windows(llvm::sys::path::Style::native)) {
// Fixing a problem with "clang C:test.c" on Windows.
// Stat("C:") does not recognize "C:" as a valid directory
if (DirName.size() > 1 && DirName.back() == ':' &&
DirName.equals_insensitive(llvm::sys::path::root_name(DirName))) {
DirNameStr = DirName.str() + '.';
DirName = *DirNameStr;
// See if there was already an entry in the map. Note that the map
// contains both virtual and real directories.
auto SeenDirInsertResult =
SeenDirEntries.insert({DirName, std::errc::no_such_file_or_directory});
if (!SeenDirInsertResult.second) {
if (SeenDirInsertResult.first->second)
return DirectoryEntryRef(*SeenDirInsertResult.first);
return llvm::errorCodeToError(SeenDirInsertResult.first->second.getError());
// We've not seen this before. Fill it in.
auto &NamedDirEnt = *SeenDirInsertResult.first;
assert(!NamedDirEnt.second && "should be newly-created");
// Get the null-terminated directory name as stored as the key of the
// SeenDirEntries map.
StringRef InterndDirName = NamedDirEnt.first();
// Check to see if the directory exists.
llvm::vfs::Status Status;
auto statError = getStatValue(InterndDirName, Status, false,
nullptr /*directory lookup*/);
if (statError) {
// There's no real directory at the given path.
if (CacheFailure)
NamedDirEnt.second = statError;
return llvm::errorCodeToError(statError);
// It exists. See if we have already opened a directory with the
// same inode (this occurs on Unix-like systems when one dir is
// symlinked to another, for example) or the same path (on
// Windows).
DirectoryEntry *&UDE = UniqueRealDirs[Status.getUniqueID()];
if (!UDE) {
// We don't have this directory yet, add it. We use the string
// key from the SeenDirEntries map as the string.
UDE = new (DirsAlloc.Allocate()) DirectoryEntry();
UDE->Name = InterndDirName;
NamedDirEnt.second = *UDE;
return DirectoryEntryRef(NamedDirEnt);
llvm::ErrorOr<const DirectoryEntry *>
FileManager::getDirectory(StringRef DirName, bool CacheFailure) {
auto Result = getDirectoryRef(DirName, CacheFailure);
if (Result)
return &Result->getDirEntry();
return llvm::errorToErrorCode(Result.takeError());
llvm::ErrorOr<const FileEntry *>
FileManager::getFile(StringRef Filename, bool openFile, bool CacheFailure) {
auto Result = getFileRef(Filename, openFile, CacheFailure);
if (Result)
return &Result->getFileEntry();
return llvm::errorToErrorCode(Result.takeError());
FileManager::getFileRef(StringRef Filename, bool openFile, bool CacheFailure) {
// See if there is already an entry in the map.
auto SeenFileInsertResult =
SeenFileEntries.insert({Filename, std::errc::no_such_file_or_directory});
if (!SeenFileInsertResult.second) {
if (!SeenFileInsertResult.first->second)
return llvm::errorCodeToError(
// Construct and return and FileEntryRef, unless it's a redirect to another
// filename.
FileEntryRef::MapValue Value = *SeenFileInsertResult.first->second;
if (LLVM_LIKELY(<FileEntry *>()))
return FileEntryRef(*SeenFileInsertResult.first);
return FileEntryRef(*reinterpret_cast<const FileEntryRef::MapEntry *>(
Value.V.get<const void *>()));
// We've not seen this before. Fill it in.
auto *NamedFileEnt = &*SeenFileInsertResult.first;
assert(!NamedFileEnt->second && "should be newly-created");
// Get the null-terminated file name as stored as the key of the
// SeenFileEntries map.
StringRef InterndFileName = NamedFileEnt->first();
// Look up the directory for the file. When looking up something like
// sys/foo.h we'll discover all of the search directories that have a 'sys'
// subdirectory. This will let us avoid having to waste time on known-to-fail
// searches when we go to find sys/bar.h, because all the search directories
// without a 'sys' subdir will get a cached failure result.
auto DirInfoOrErr = getDirectoryFromFile(*this, Filename, CacheFailure);
if (!DirInfoOrErr) { // Directory doesn't exist, file can't exist.
std::error_code Err = errorToErrorCode(DirInfoOrErr.takeError());
if (CacheFailure)
NamedFileEnt->second = Err;
return llvm::errorCodeToError(Err);
DirectoryEntryRef DirInfo = *DirInfoOrErr;
// FIXME: Use the directory info to prune this, before doing the stat syscall.
// FIXME: This will reduce the # syscalls.
// Check to see if the file exists.
std::unique_ptr<llvm::vfs::File> F;
llvm::vfs::Status Status;
auto statError = getStatValue(InterndFileName, Status, true,
openFile ? &F : nullptr);
if (statError) {
// There's no real file at the given path.
if (CacheFailure)
NamedFileEnt->second = statError;
return llvm::errorCodeToError(statError);
assert((openFile || !F) && "undesired open file");
// It exists. See if we have already opened a file with the same inode.
// This occurs when one dir is symlinked to another, for example.
FileEntry *&UFE = UniqueRealFiles[Status.getUniqueID()];
bool ReusingEntry = UFE != nullptr;
if (!UFE)
UFE = new (FilesAlloc.Allocate()) FileEntry();
if (Status.getName() == Filename) {
// The name matches. Set the FileEntry.
NamedFileEnt->second = FileEntryRef::MapValue(*UFE, DirInfo);
} else {
// Name mismatch. We need a redirect. First grab the actual entry we want
// to return.
// This redirection logic intentionally leaks the external name of a
// redirected file that uses 'use-external-name' in \a
// vfs::RedirectionFileSystem. This allows clang to report the external
// name to users (in diagnostics) and to tools that don't have access to
// the VFS (in debug info and dependency '.d' files).
// FIXME: This is pretty complex and has some very complicated interactions
// with the rest of clang. It's also inconsistent with how "real"
// filesystems behave and confuses parts of clang expect to see the
// name-as-accessed on the \a FileEntryRef.
// Further, it isn't *just* external names, but will also give back absolute
// paths when a relative path was requested - the check is comparing the
// name from the status, which is passed an absolute path resolved from the
// current working directory. `clang-apply-replacements` appears to depend
// on this behaviour, though it's adjusting the working directory, which is
// definitely not supported. Once that's fixed this hack should be able to
// be narrowed to only when there's an externally mapped name given back.
// A potential plan to remove this is as follows -
// - Add API to determine if the name has been rewritten by the VFS.
// - Fix `clang-apply-replacements` to pass down the absolute path rather
// than changing the CWD. Narrow this hack down to just externally
// mapped paths.
// - Expose the requested filename. One possibility would be to allow
// redirection-FileEntryRefs to be returned, rather than returning
// the pointed-at-FileEntryRef, and customizing `getName()` to look
// through the indirection.
// - Update callers such as `HeaderSearch::findUsableModuleForHeader()`
// to explicitly use the requested filename rather than just using
// `getName()`.
// - Add a `FileManager::getExternalPath` API for explicitly getting the
// remapped external filename when there is one available. Adopt it in
// callers like diagnostics/deps reporting instead of calling
// `getName()` directly.
// - Switch the meaning of `FileEntryRef::getName()` to get the requested
// name, not the external name. Once that sticks, revert callers that
// want the requested name back to calling `getName()`.
// - Update the VFS to always return the requested name. This could also
// return the external name, or just have an API to request it
// lazily. The latter has the benefit of making accesses of the
// external path easily tracked, but may also require extra work than
// just returning up front.
// - (Optionally) Add an API to VFS to get the external filename lazily
// and update `FileManager::getExternalPath()` to use it instead. This
// has the benefit of making such accesses easily tracked, though isn't
// necessarily required (and could cause extra work than just adding to
// eg. `vfs::Status` up front).
auto &Redirection =
.insert({Status.getName(), FileEntryRef::MapValue(*UFE, DirInfo)})
assert(Redirection.second-><FileEntry *>() &&
"filename redirected to a non-canonical filename?");
assert(Redirection.second->V.get<FileEntry *>() == UFE &&
"filename from getStatValue() refers to wrong file");
// Cache the redirection in the previously-inserted entry, still available
// in the tentative return value.
NamedFileEnt->second = FileEntryRef::MapValue(Redirection);
// Fix the tentative return value.
NamedFileEnt = &Redirection;
FileEntryRef ReturnedRef(*NamedFileEnt);
if (ReusingEntry) { // Already have an entry with this inode, return it.
// FIXME: This hack ensures that `getDir()` will use the path that was
// used to lookup this file, even if we found a file by different path
// first. This is required in order to find a module's structure when its
// headers/module map are mapped in the VFS.
// See above for how this will eventually be removed. `IsVFSMapped`
// *cannot* be narrowed to `ExposesExternalVFSPath` as crash reproducers
// also depend on this logic and they have `use-external-paths: false`.
if (&DirInfo.getDirEntry() != UFE->Dir && Status.IsVFSMapped)
UFE->Dir = &DirInfo.getDirEntry();
// Always update LastRef to the last name by which a file was accessed.
// FIXME: Neither this nor always using the first reference is correct; we
// want to switch towards a design where we return a FileName object that
// encapsulates both the name by which the file was accessed and the
// corresponding FileEntry.
// FIXME: LastRef should be removed from FileEntry once all clients adopt
// FileEntryRef.
UFE->LastRef = ReturnedRef;
return ReturnedRef;
// Otherwise, we don't have this file yet, add it.
UFE->LastRef = ReturnedRef;
UFE->Size = Status.getSize();
UFE->ModTime = llvm::sys::toTimeT(Status.getLastModificationTime());
UFE->Dir = &DirInfo.getDirEntry();
UFE->UID = NextFileUID++;
UFE->UniqueID = Status.getUniqueID();
UFE->IsNamedPipe = Status.getType() == llvm::sys::fs::file_type::fifo_file;
UFE->File = std::move(F);
if (UFE->File) {
if (auto PathName = UFE->File->getName())
fillRealPathName(UFE, *PathName);
} else if (!openFile) {
// We should still fill the path even if we aren't opening the file.
fillRealPathName(UFE, InterndFileName);
return ReturnedRef;
llvm::Expected<FileEntryRef> FileManager::getSTDIN() {
// Only read stdin once.
if (STDIN)
return *STDIN;
std::unique_ptr<llvm::MemoryBuffer> Content;
if (auto ContentOrError = llvm::MemoryBuffer::getSTDIN())
Content = std::move(*ContentOrError);
return llvm::errorCodeToError(ContentOrError.getError());
STDIN = getVirtualFileRef(Content->getBufferIdentifier(),
Content->getBufferSize(), 0);
FileEntry &FE = const_cast<FileEntry &>(STDIN->getFileEntry());
FE.Content = std::move(Content);
FE.IsNamedPipe = true;
return *STDIN;
const FileEntry *FileManager::getVirtualFile(StringRef Filename, off_t Size,
time_t ModificationTime) {
return &getVirtualFileRef(Filename, Size, ModificationTime).getFileEntry();
FileEntryRef FileManager::getVirtualFileRef(StringRef Filename, off_t Size,
time_t ModificationTime) {
// See if there is already an entry in the map for an existing file.
auto &NamedFileEnt = *SeenFileEntries.insert(
{Filename, std::errc::no_such_file_or_directory}).first;
if (NamedFileEnt.second) {
FileEntryRef::MapValue Value = *NamedFileEnt.second;
if (LLVM_LIKELY(<FileEntry *>()))
return FileEntryRef(NamedFileEnt);
return FileEntryRef(*reinterpret_cast<const FileEntryRef::MapEntry *>(
Value.V.get<const void *>()));
// We've not seen this before, or the file is cached as non-existent.
FileEntry *UFE = nullptr;
// Now that all ancestors of Filename are in the cache, the
// following call is guaranteed to find the DirectoryEntry from the
// cache. A virtual file can also have an empty filename, that could come
// from a source location preprocessor directive with an empty filename as
// an example, so we need to pretend it has a name to ensure a valid directory
// entry can be returned.
auto DirInfo = expectedToOptional(getDirectoryFromFile(
*this, Filename.empty() ? "." : Filename, /*CacheFailure=*/true));
assert(DirInfo &&
"The directory of a virtual file should already be in the cache.");
// Check to see if the file exists. If so, drop the virtual file
llvm::vfs::Status Status;
const char *InterndFileName = NamedFileEnt.first().data();
if (!getStatValue(InterndFileName, Status, true, nullptr)) {
Status = llvm::vfs::Status(
Status.getName(), Status.getUniqueID(),
Status.getUser(), Status.getGroup(), Size,
Status.getType(), Status.getPermissions());
auto &RealFE = UniqueRealFiles[Status.getUniqueID()];
if (RealFE) {
// If we had already opened this file, close it now so we don't
// leak the descriptor. We're not going to use the file
// descriptor anyway, since this is a virtual file.
if (RealFE->File)
// If we already have an entry with this inode, return it.
// FIXME: Surely this should add a reference by the new name, and return
// it instead...
NamedFileEnt.second = FileEntryRef::MapValue(*RealFE, *DirInfo);
return FileEntryRef(NamedFileEnt);
// File exists, but no entry - create it.
RealFE = new (FilesAlloc.Allocate()) FileEntry();
RealFE->UniqueID = Status.getUniqueID();
RealFE->IsNamedPipe =
Status.getType() == llvm::sys::fs::file_type::fifo_file;
fillRealPathName(RealFE, Status.getName());
UFE = RealFE;
} else {
// File does not exist, create a virtual entry.
UFE = new (FilesAlloc.Allocate()) FileEntry();
NamedFileEnt.second = FileEntryRef::MapValue(*UFE, *DirInfo);
UFE->LastRef = FileEntryRef(NamedFileEnt);
UFE->Size = Size;
UFE->ModTime = ModificationTime;
UFE->Dir = &DirInfo->getDirEntry();
UFE->UID = NextFileUID++;
return FileEntryRef(NamedFileEnt);
llvm::Optional<FileEntryRef> FileManager::getBypassFile(FileEntryRef VF) {
// Stat of the file and return nullptr if it doesn't exist.
llvm::vfs::Status Status;
if (getStatValue(VF.getName(), Status, /*isFile=*/true, /*F=*/nullptr))
return None;
if (!SeenBypassFileEntries)
SeenBypassFileEntries = std::make_unique<
// If we've already bypassed just use the existing one.
auto Insertion = SeenBypassFileEntries->insert(
{VF.getName(), std::errc::no_such_file_or_directory});
if (!Insertion.second)
return FileEntryRef(*Insertion.first);
// Fill in the new entry from the stat.
FileEntry *BFE = new (FilesAlloc.Allocate()) FileEntry();
Insertion.first->second = FileEntryRef::MapValue(*BFE, VF.getDir());
BFE->LastRef = FileEntryRef(*Insertion.first);
BFE->Size = Status.getSize();
BFE->Dir = VF.getFileEntry().Dir;
BFE->ModTime = llvm::sys::toTimeT(Status.getLastModificationTime());
BFE->UID = NextFileUID++;
// Save the entry in the bypass table and return.
return FileEntryRef(*Insertion.first);
bool FileManager::FixupRelativePath(SmallVectorImpl<char> &path) const {
StringRef pathRef(, path.size());
if (FileSystemOpts.WorkingDir.empty()
|| llvm::sys::path::is_absolute(pathRef))
return false;
SmallString<128> NewPath(FileSystemOpts.WorkingDir);
llvm::sys::path::append(NewPath, pathRef);
path = NewPath;
return true;
bool FileManager::makeAbsolutePath(SmallVectorImpl<char> &Path) const {
bool Changed = FixupRelativePath(Path);
if (!llvm::sys::path::is_absolute(StringRef(, Path.size()))) {
Changed = true;
return Changed;
void FileManager::fillRealPathName(FileEntry *UFE, llvm::StringRef FileName) {
llvm::SmallString<128> AbsPath(FileName);
// This is not the same as `VFS::getRealPath()`, which resolves symlinks
// but can be very expensive on real file systems.
// FIXME: the semantic of RealPathName is unclear, and the name might be
// misleading. We need to clean up the interface here.
llvm::sys::path::remove_dots(AbsPath, /*remove_dot_dot=*/true);
UFE->RealPathName = std::string(AbsPath.str());
FileManager::getBufferForFile(const FileEntry *Entry, bool isVolatile,
bool RequiresNullTerminator) {
// If the content is living on the file entry, return a reference to it.
if (Entry->Content)
return llvm::MemoryBuffer::getMemBuffer(Entry->Content->getMemBufferRef());
uint64_t FileSize = Entry->getSize();
// If there's a high enough chance that the file have changed since we
// got its size, force a stat before opening it.
if (isVolatile || Entry->isNamedPipe())
FileSize = -1;
StringRef Filename = Entry->getName();
// If the file is already open, use the open file descriptor.
if (Entry->File) {
auto Result = Entry->File->getBuffer(Filename, FileSize,
RequiresNullTerminator, isVolatile);
return Result;
// Otherwise, open the file.
return getBufferForFileImpl(Filename, FileSize, isVolatile,
FileManager::getBufferForFileImpl(StringRef Filename, int64_t FileSize,
bool isVolatile,
bool RequiresNullTerminator) {
if (FileSystemOpts.WorkingDir.empty())
return FS->getBufferForFile(Filename, FileSize, RequiresNullTerminator,
SmallString<128> FilePath(Filename);
return FS->getBufferForFile(FilePath, FileSize, RequiresNullTerminator,
/// getStatValue - Get the 'stat' information for the specified path,
/// using the cache to accelerate it if possible. This returns true
/// if the path points to a virtual file or does not exist, or returns
/// false if it's an existent real file. If FileDescriptor is NULL,
/// do directory look-up instead of file look-up.
FileManager::getStatValue(StringRef Path, llvm::vfs::Status &Status,
bool isFile, std::unique_ptr<llvm::vfs::File> *F) {
// FIXME: FileSystemOpts shouldn't be passed in here, all paths should be
// absolute!
if (FileSystemOpts.WorkingDir.empty())
return FileSystemStatCache::get(Path, Status, isFile, F,
StatCache.get(), *FS);
SmallString<128> FilePath(Path);
return FileSystemStatCache::get(FilePath.c_str(), Status, isFile, F,
StatCache.get(), *FS);
FileManager::getNoncachedStatValue(StringRef Path,
llvm::vfs::Status &Result) {
SmallString<128> FilePath(Path);
llvm::ErrorOr<llvm::vfs::Status> S = FS->status(FilePath.c_str());
if (!S)
return S.getError();
Result = *S;
return std::error_code();
void FileManager::GetUniqueIDMapping(
SmallVectorImpl<const FileEntry *> &UIDToFiles) const {
// Map file entries
for (llvm::StringMap<llvm::ErrorOr<FileEntryRef::MapValue>,
FE = SeenFileEntries.begin(),
FEEnd = SeenFileEntries.end();
FE != FEEnd; ++FE)
if (llvm::ErrorOr<FileEntryRef::MapValue> Entry = FE->getValue()) {
if (const auto *FE = Entry->V.dyn_cast<FileEntry *>())
UIDToFiles[FE->getUID()] = FE;
// Map virtual file entries
for (const auto &VFE : VirtualFileEntries)
UIDToFiles[VFE->getUID()] = VFE;
StringRef FileManager::getCanonicalName(const DirectoryEntry *Dir) {
llvm::DenseMap<const void *, llvm::StringRef>::iterator Known
= CanonicalNames.find(Dir);
if (Known != CanonicalNames.end())
return Known->second;
StringRef CanonicalName(Dir->getName());
SmallString<4096> CanonicalNameBuf;
if (!FS->getRealPath(Dir->getName(), CanonicalNameBuf))
CanonicalName = CanonicalNameBuf.str().copy(CanonicalNameStorage);
CanonicalNames.insert({Dir, CanonicalName});
return CanonicalName;
StringRef FileManager::getCanonicalName(const FileEntry *File) {
llvm::DenseMap<const void *, llvm::StringRef>::iterator Known
= CanonicalNames.find(File);
if (Known != CanonicalNames.end())
return Known->second;
StringRef CanonicalName(File->getName());
SmallString<4096> CanonicalNameBuf;
if (!FS->getRealPath(File->getName(), CanonicalNameBuf))
CanonicalName = CanonicalNameBuf.str().copy(CanonicalNameStorage);
CanonicalNames.insert({File, CanonicalName});
return CanonicalName;
void FileManager::PrintStats() const {
llvm::errs() << "\n*** File Manager Stats:\n";
llvm::errs() << UniqueRealFiles.size() << " real files found, "
<< UniqueRealDirs.size() << " real dirs found.\n";
llvm::errs() << VirtualFileEntries.size() << " virtual files found, "
<< VirtualDirectoryEntries.size() << " virtual dirs found.\n";
llvm::errs() << NumDirLookups << " dir lookups, "
<< NumDirCacheMisses << " dir cache misses.\n";
llvm::errs() << NumFileLookups << " file lookups, "
<< NumFileCacheMisses << " file cache misses.\n";
//llvm::errs() << PagesMapped << BytesOfPagesMapped << FSLookups;