blob: 8906be3aaa25561e05754e6a8348931df3a10ded [file] [log] [blame]
//===- FileOutputBuffer.cpp - File Output Buffer ----------------*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// Utility for creating a in-memory buffer that will be written to a file.
#include "llvm/Support/FileOutputBuffer.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/Memory.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/Signals.h"
#include <system_error>
#if !defined(_MSC_VER) && !defined(__MINGW32__)
#include <unistd.h>
#include <io.h>
using namespace llvm;
using namespace llvm::sys;
// A FileOutputBuffer which creates a temporary file in the same directory
// as the final output file. The final output file is atomically replaced
// with the temporary file on commit().
class OnDiskBuffer : public FileOutputBuffer {
OnDiskBuffer(StringRef Path, StringRef TempPath,
std::unique_ptr<fs::mapped_file_region> Buf)
: FileOutputBuffer(Path), Buffer(std::move(Buf)), TempPath(TempPath) {}
static Expected<std::unique_ptr<OnDiskBuffer>>
create(StringRef Path, size_t Size, unsigned Mode);
uint8_t *getBufferStart() const override { return (uint8_t *)Buffer->data(); }
uint8_t *getBufferEnd() const override {
return (uint8_t *)Buffer->data() + Buffer->size();
size_t getBufferSize() const override { return Buffer->size(); }
Error commit() override {
// Unmap buffer, letting OS flush dirty pages to file on disk.
// Atomically replace the existing file with the new one.
auto EC = fs::rename(TempPath, FinalPath);
return errorCodeToError(EC);
~OnDiskBuffer() override {
// Close the mapping before deleting the temp file, so that the removal
// succeeds.
std::unique_ptr<fs::mapped_file_region> Buffer;
std::string TempPath;
// A FileOutputBuffer which keeps data in memory and writes to the final
// output file on commit(). This is used only when we cannot use OnDiskBuffer.
class InMemoryBuffer : public FileOutputBuffer {
InMemoryBuffer(StringRef Path, MemoryBlock Buf, unsigned Mode)
: FileOutputBuffer(Path), Buffer(Buf), Mode(Mode) {}
static Expected<std::unique_ptr<InMemoryBuffer>>
create(StringRef Path, size_t Size, unsigned Mode) {
std::error_code EC;
MemoryBlock MB = Memory::allocateMappedMemory(
Size, nullptr, sys::Memory::MF_READ | sys::Memory::MF_WRITE, EC);
if (EC)
return errorCodeToError(EC);
return llvm::make_unique<InMemoryBuffer>(Path, MB, Mode);
uint8_t *getBufferStart() const override { return (uint8_t *)Buffer.base(); }
uint8_t *getBufferEnd() const override {
return (uint8_t *)Buffer.base() + Buffer.size();
size_t getBufferSize() const override { return Buffer.size(); }
Error commit() override {
int FD;
std::error_code EC;
if (auto EC = openFileForWrite(FinalPath, FD, fs::F_None, Mode))
return errorCodeToError(EC);
raw_fd_ostream OS(FD, /*shouldClose=*/true, /*unbuffered=*/true);
OS << StringRef((const char *)Buffer.base(), Buffer.size());
return Error::success();
OwningMemoryBlock Buffer;
unsigned Mode;
OnDiskBuffer::create(StringRef Path, size_t Size, unsigned Mode) {
// Create new file in same directory but with random name.
SmallString<128> TempPath;
int FD;
if (auto EC = fs::createUniqueFile(Path + ".tmp%%%%%%%", FD, TempPath, Mode))
return errorCodeToError(EC);
#ifndef LLVM_ON_WIN32
// On Windows, CreateFileMapping (the mmap function on Windows)
// automatically extends the underlying file. We don't need to
// extend the file beforehand. _chsize (ftruncate on Windows) is
// pretty slow just like it writes specified amount of bytes,
// so we should avoid calling that function.
if (auto EC = fs::resize_file(FD, Size))
return errorCodeToError(EC);
// Mmap it.
std::error_code EC;
auto MappedFile = llvm::make_unique<fs::mapped_file_region>(
FD, fs::mapped_file_region::readwrite, Size, 0, EC);
if (EC)
return errorCodeToError(EC);
return llvm::make_unique<OnDiskBuffer>(Path, TempPath, std::move(MappedFile));
// Create an instance of FileOutputBuffer.
FileOutputBuffer::create(StringRef Path, size_t Size, unsigned Flags) {
unsigned Mode = fs::all_read | fs::all_write;
if (Flags & F_executable)
Mode |= fs::all_exe;
fs::file_status Stat;
fs::status(Path, Stat);
// Usually, we want to create OnDiskBuffer to create a temporary file in
// the same directory as the destination file and atomically replaces it
// by rename(2).
// However, if the destination file is a special file, we don't want to
// use rename (e.g. we don't want to replace /dev/null with a regular
// file.) If that's the case, we create an in-memory buffer, open the
// destination file and write to it on commit().
switch (Stat.type()) {
case fs::file_type::directory_file:
return errorCodeToError(errc::is_a_directory);
case fs::file_type::regular_file:
case fs::file_type::file_not_found:
case fs::file_type::status_error:
return OnDiskBuffer::create(Path, Size, Mode);
return InMemoryBuffer::create(Path, Size, Mode);