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 ErrorOr<std::unique_ptr<FileOutputBuffer>>
38 FileOutputBuffer::create(StringRef FilePath, size_t Size, unsigned Flags) {
39   // If file already exists, it must be a regular file (to be mappable).
40   sys::fs::file_status Stat;
41   std::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   EC = sys::fs::remove(FilePath);
61   if (EC)
62     return EC;
63 
64   unsigned Mode = sys::fs::all_read | sys::fs::all_write;
65   // If requested, make the output file executable.
66   if (Flags & F_executable)
67     Mode |= sys::fs::all_exe;
68 
69   // Create new file in same directory but with random name.
70   SmallString<128> TempFilePath;
71   int FD;
72   EC = sys::fs::createUniqueFile(Twine(FilePath) + ".tmp%%%%%%%", FD,
73                                  TempFilePath, Mode);
74   if (EC)
75     return EC;
76 
77 #ifndef LLVM_ON_WIN32
78   // On Windows, CreateFileMapping (the mmap function on Windows)
79   // automatically extends the underlying file. We don't need to
80   // extend the file beforehand. _chsize (ftruncate on Windows) is
81   // pretty slow just like it writes specified amount of bytes,
82   // so we should avoid calling that.
83   EC = sys::fs::resize_file(FD, Size);
84   if (EC)
85     return EC;
86 #endif
87 
88   auto MappedFile = llvm::make_unique<mapped_file_region>(
89       FD, mapped_file_region::readwrite, Size, 0, EC);
90   int Ret = close(FD);
91   if (EC)
92     return EC;
93   if (Ret)
94     return std::error_code(errno, std::generic_category());
95 
96   std::unique_ptr<FileOutputBuffer> Buf(
97       new FileOutputBuffer(std::move(MappedFile), FilePath, TempFilePath));
98   return std::move(Buf);
99 }
100 
101 std::error_code FileOutputBuffer::commit() {
102   // Unmap buffer, letting OS flush dirty pages to file on disk.
103   Region.reset();
104 
105 
106   // Rename file to final name.
107   return sys::fs::rename(Twine(TempPath), Twine(FinalPath));
108 }
109 } // namespace
110