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/STLExtras.h"
16 #include "llvm/ADT/SmallString.h"
17 #include "llvm/Support/Errc.h"
18 #include <system_error>
19 
20 #if !defined(_MSC_VER) && !defined(__MINGW32__)
21 #include <unistd.h>
22 #else
23 #include <io.h>
24 #endif
25 
26 using llvm::sys::fs::mapped_file_region;
27 
28 namespace llvm {
29 FileOutputBuffer::FileOutputBuffer(std::unique_ptr<mapped_file_region> R,
30                                    StringRef Path, StringRef TmpPath)
31     : Region(std::move(R)), FinalPath(Path), TempPath(TmpPath) {}
32 
33 FileOutputBuffer::~FileOutputBuffer() {
34   sys::fs::remove(Twine(TempPath));
35 }
36 
37 std::error_code
38 FileOutputBuffer::create(StringRef FilePath, size_t Size,
39                          std::unique_ptr<FileOutputBuffer> &Result,
40                          unsigned Flags) {
41   // If file already exists, it must be a regular file (to be mappable).
42   sys::fs::file_status Stat;
43   std::error_code EC = sys::fs::status(FilePath, Stat);
44   switch (Stat.type()) {
45     case sys::fs::file_type::file_not_found:
46       // If file does not exist, we'll create one.
47       break;
48     case sys::fs::file_type::regular_file: {
49         // If file is not currently writable, error out.
50         // FIXME: There is no sys::fs:: api for checking this.
51         // FIXME: In posix, you use the access() call to check this.
52       }
53       break;
54     default:
55       if (EC)
56         return EC;
57       else
58         return make_error_code(errc::operation_not_permitted);
59   }
60 
61   // Delete target file.
62   EC = sys::fs::remove(FilePath);
63   if (EC)
64     return EC;
65 
66   unsigned Mode = sys::fs::all_read | sys::fs::all_write;
67   // If requested, make the output file executable.
68   if (Flags & F_executable)
69     Mode |= sys::fs::all_exe;
70 
71   // Create new file in same directory but with random name.
72   SmallString<128> TempFilePath;
73   int FD;
74   EC = sys::fs::createUniqueFile(Twine(FilePath) + ".tmp%%%%%%%", FD,
75                                  TempFilePath, Mode);
76   if (EC)
77     return EC;
78 
79 #ifndef LLVM_ON_WIN32
80   // On Windows, CreateFileMapping (the mmap function on Windows)
81   // automatically extends the underlying file. We don't need to
82   // extend the file beforehand. _chsize (ftruncate on Windows) is
83   // pretty slow just like it writes specified amount of bytes,
84   // so we should avoid calling that.
85   EC = sys::fs::resize_file(FD, Size);
86   if (EC)
87     return EC;
88 #endif
89 
90   auto MappedFile = llvm::make_unique<mapped_file_region>(
91       FD, mapped_file_region::readwrite, Size, 0, EC);
92   int Ret = close(FD);
93   if (EC)
94     return EC;
95   if (Ret)
96     return std::error_code(errno, std::generic_category());
97 
98   Result.reset(
99       new FileOutputBuffer(std::move(MappedFile), FilePath, TempFilePath));
100 
101   return std::error_code();
102 }
103 
104 std::error_code FileOutputBuffer::commit() {
105   // Unmap buffer, letting OS flush dirty pages to file on disk.
106   Region.reset();
107 
108 
109   // Rename file to final name.
110   return sys::fs::rename(Twine(TempPath), Twine(FinalPath));
111 }
112 } // namespace
113