197 lines · cpp
1//===- FileOutputBuffer.cpp - File Output Buffer ----------------*- C++ -*-===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8//9// Utility for creating a in-memory buffer that will be written to a file.10//11//===----------------------------------------------------------------------===//12 13#include "llvm/Support/FileOutputBuffer.h"14#include "llvm/Support/Errc.h"15#include "llvm/Support/FileSystem.h"16#include "llvm/Support/Memory.h"17#include "llvm/Support/TimeProfiler.h"18#include <system_error>19 20#if !defined(_MSC_VER) && !defined(__MINGW32__)21#include <unistd.h>22#else23#include <io.h>24#endif25 26using namespace llvm;27using namespace llvm::sys;28 29namespace {30// A FileOutputBuffer which creates a temporary file in the same directory31// as the final output file. The final output file is atomically replaced32// with the temporary file on commit().33class OnDiskBuffer : public FileOutputBuffer {34public:35 OnDiskBuffer(StringRef Path, fs::TempFile Temp, fs::mapped_file_region Buf)36 : FileOutputBuffer(Path), Buffer(std::move(Buf)), Temp(std::move(Temp)) {}37 38 uint8_t *getBufferStart() const override { return (uint8_t *)Buffer.data(); }39 40 uint8_t *getBufferEnd() const override {41 return (uint8_t *)Buffer.data() + Buffer.size();42 }43 44 size_t getBufferSize() const override { return Buffer.size(); }45 46 Error commit() override {47 llvm::TimeTraceScope timeScope("Commit buffer to disk");48 49 // Unmap buffer, letting OS flush dirty pages to file on disk.50 Buffer.unmap();51 52 // Atomically replace the existing file with the new one.53 return Temp.keep(FinalPath);54 }55 56 ~OnDiskBuffer() override {57 // Close the mapping before deleting the temp file, so that the removal58 // succeeds.59 Buffer.unmap();60 consumeError(Temp.discard());61 }62 63 void discard() override {64 // Delete the temp file if it still was open, but keeping the mapping65 // active.66 consumeError(Temp.discard());67 }68 69private:70 fs::mapped_file_region Buffer;71 fs::TempFile Temp;72};73 74// A FileOutputBuffer which keeps data in memory and writes to the final75// output file on commit(). This is used only when we cannot use OnDiskBuffer.76class InMemoryBuffer : public FileOutputBuffer {77public:78 InMemoryBuffer(StringRef Path, MemoryBlock Buf, std::size_t BufSize,79 unsigned Mode)80 : FileOutputBuffer(Path), Buffer(Buf), BufferSize(BufSize),81 Mode(Mode) {}82 83 uint8_t *getBufferStart() const override { return (uint8_t *)Buffer.base(); }84 85 uint8_t *getBufferEnd() const override {86 return (uint8_t *)Buffer.base() + BufferSize;87 }88 89 size_t getBufferSize() const override { return BufferSize; }90 91 Error commit() override {92 if (FinalPath == "-") {93 llvm::outs() << StringRef((const char *)Buffer.base(), BufferSize);94 llvm::outs().flush();95 return Error::success();96 }97 98 using namespace sys::fs;99 int FD;100 std::error_code EC;101 if (auto EC =102 openFileForWrite(FinalPath, FD, CD_CreateAlways, OF_Delete, Mode))103 return errorCodeToError(EC);104 raw_fd_ostream OS(FD, /*shouldClose=*/true, /*unbuffered=*/true);105 OS << StringRef((const char *)Buffer.base(), BufferSize);106 return Error::success();107 }108 109private:110 // Buffer may actually contain a larger memory block than BufferSize111 OwningMemoryBlock Buffer;112 size_t BufferSize;113 unsigned Mode;114};115} // namespace116 117static Expected<std::unique_ptr<InMemoryBuffer>>118createInMemoryBuffer(StringRef Path, size_t Size, unsigned Mode) {119 std::error_code EC;120 MemoryBlock MB = Memory::allocateMappedMemory(121 Size, nullptr, sys::Memory::MF_READ | sys::Memory::MF_WRITE, EC);122 if (EC)123 return errorCodeToError(EC);124 return std::make_unique<InMemoryBuffer>(Path, MB, Size, Mode);125}126 127static Expected<std::unique_ptr<FileOutputBuffer>>128createOnDiskBuffer(StringRef Path, size_t Size, unsigned Mode) {129 Expected<fs::TempFile> FileOrErr =130 fs::TempFile::create(Path + ".tmp%%%%%%%", Mode);131 if (!FileOrErr)132 return FileOrErr.takeError();133 fs::TempFile File = std::move(*FileOrErr);134 135 if (auto EC = fs::resize_file_before_mapping_readwrite(File.FD, Size)) {136 consumeError(File.discard());137 return errorCodeToError(EC);138 }139 140 // Mmap it.141 std::error_code EC;142 fs::mapped_file_region MappedFile =143 fs::mapped_file_region(fs::convertFDToNativeFile(File.FD),144 fs::mapped_file_region::readwrite, Size, 0, EC);145 146 // mmap(2) can fail if the underlying filesystem does not support it.147 // If that happens, we fall back to in-memory buffer as the last resort.148 if (EC) {149 consumeError(File.discard());150 return createInMemoryBuffer(Path, Size, Mode);151 }152 153 return std::make_unique<OnDiskBuffer>(Path, std::move(File),154 std::move(MappedFile));155}156 157// Create an instance of FileOutputBuffer.158Expected<std::unique_ptr<FileOutputBuffer>>159FileOutputBuffer::create(StringRef Path, size_t Size, unsigned Flags) {160 // Handle "-" as stdout just like llvm::raw_ostream does.161 if (Path == "-")162 return createInMemoryBuffer("-", Size, /*Mode=*/0);163 164 unsigned Mode = fs::all_read | fs::all_write;165 if (Flags & F_executable)166 Mode |= fs::all_exe;167 168 // If Size is zero, don't use mmap which will fail with EINVAL.169 if (Size == 0)170 return createInMemoryBuffer(Path, Size, Mode);171 172 fs::file_status Stat;173 fs::status(Path, Stat);174 175 // Usually, we want to create OnDiskBuffer to create a temporary file in176 // the same directory as the destination file and atomically replaces it177 // by rename(2).178 //179 // However, if the destination file is a special file, we don't want to180 // use rename (e.g. we don't want to replace /dev/null with a regular181 // file.) If that's the case, we create an in-memory buffer, open the182 // destination file and write to it on commit().183 switch (Stat.type()) {184 case fs::file_type::directory_file:185 return errorCodeToError(errc::is_a_directory);186 case fs::file_type::regular_file:187 case fs::file_type::file_not_found:188 case fs::file_type::status_error:189 if (Flags & F_mmap)190 return createInMemoryBuffer(Path, Size, Mode);191 else192 return createOnDiskBuffer(Path, Size, Mode);193 default:194 return createInMemoryBuffer(Path, Size, Mode);195 }196}197