FileOutputBuffer.cpp revision 263508 
1//===- FileOutputBuffer.cpp - File Output Buffer ----------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// Utility for creating a in-memory buffer that will be written to a file.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Support/FileOutputBuffer.h"
15#include "llvm/ADT/OwningPtr.h"
16#include "llvm/ADT/SmallVector.h"
17#include "llvm/Support/raw_ostream.h"
18#include "llvm/Support/system_error.h"
19
20using llvm::sys::fs::mapped_file_region;
21
22namespace llvm {
23FileOutputBuffer::FileOutputBuffer(mapped_file_region * R,
24                                   StringRef Path, StringRef TmpPath)
25  : Region(R)
26  , FinalPath(Path)
27  , TempPath(TmpPath) {
28}
29
30FileOutputBuffer::~FileOutputBuffer() {
31  bool Existed;
32  sys::fs::remove(Twine(TempPath), Existed);
33}
34
35error_code FileOutputBuffer::create(StringRef FilePath,
36                                    size_t Size,
37                                    OwningPtr<FileOutputBuffer> &Result,
38                                    unsigned Flags) {
39  // If file already exists, it must be a regular file (to be mappable).
40  sys::fs::file_status Stat;
41  error_code EC = sys::fs::status(FilePath, Stat);
42  switch (Stat.type()) {
43    case sys::fs::file_type::file_not_found:
44      // If file does not exist, we'll create one.
45      break;
46    case sys::fs::file_type::regular_file: {
47        // If file is not currently writable, error out.
48        // FIXME: There is no sys::fs:: api for checking this.
49        // FIXME: In posix, you use the access() call to check this.
50      }
51      break;
52    default:
53      if (EC)
54        return EC;
55      else
56        return make_error_code(errc::operation_not_permitted);
57  }
58
59  // Delete target file.
60  bool Existed;
61  EC = sys::fs::remove(FilePath, Existed);
62  if (EC)
63    return EC;
64
65  unsigned Mode = sys::fs::all_read | sys::fs::all_write;
66  // If requested, make the output file executable.
67  if (Flags & F_executable)
68    Mode |= sys::fs::all_exe;
69
70  // Create new file in same directory but with random name.
71  SmallString<128> TempFilePath;
72  int FD;
73  EC = sys::fs::createUniqueFile(Twine(FilePath) + ".tmp%%%%%%%", FD,
74                                 TempFilePath, Mode);
75  if (EC)
76    return EC;
77
78  OwningPtr<mapped_file_region> MappedFile(new mapped_file_region(
79      FD, true, mapped_file_region::readwrite, Size, 0, EC));
80  if (EC)
81    return EC;
82
83  Result.reset(new FileOutputBuffer(MappedFile.get(), FilePath, TempFilePath));
84  if (Result)
85    MappedFile.take();
86
87  return error_code::success();
88}
89
90error_code FileOutputBuffer::commit(int64_t NewSmallerSize) {
91  // Unmap buffer, letting OS flush dirty pages to file on disk.
92  Region.reset(0);
93
94  // If requested, resize file as part of commit.
95  if ( NewSmallerSize != -1 ) {
96    error_code EC = sys::fs::resize_file(Twine(TempPath), NewSmallerSize);
97    if (EC)
98      return EC;
99  }
100
101  // Rename file to final name.
102  return sys::fs::rename(Twine(TempPath), Twine(FinalPath));
103}
104} // namespace
105